Booting DOS from PS/2 BASIC
I have a old standalone motherboard from an IBM PS/2 Model 80. The PS/2 systems have a different kind of floppy connector and floppy drive, so one cannot simply connect a regular PC floppy drive without doing some hardware modifications. But fortunately, most of the PS/2 systems have IBM Cassette BASIC in ROM chips on the motherboard and will boot that in case everything else fails.
Someone else has already managed to boot some software from BASIC, so I took it a step further and was able to boot DOS as well. My work is based on the previous Serial Port Floppy Drive Emulation tricks to emulate the floppy drive over the COM1 port. The assembly program presented here will attempt boot a floppy image. Unfortunately I have not been able to boot the reference disk yet...
Once booted into BASIC, it is technically possible to input the complete program by hand (by keyboard):
1 data 233,157,0,184,192,7,142,192,49,219,184,1,2,185,1,0,49,210
2 data 205,19,234,0,124,0,0,251,128,250,0,117,90,128,252,2,116,5
3 data 128,252,3,117,74,83,81,82,80,80,80,232,76,0,136,224,232,71
4 data 0,136,200,232,66,0,136,232,232,61,0,136,208,232,56,0,136,240
5 data 232,51,0,90,48,246,184,0,2,247,226,137,193,88,128,252,3,116
6 data 11,232,49,0,38,136,7,67,226,247,235,9,38,138,7,232,18,0
7 data 67,226,247,88,90,89,91,48,228,248,202,2,0,234,121,0,121,0
8 data 82,186,248,3,238,186,253,3,236,36,32,132,192,116,249,90,195,82
9 data 186,250,3,236,36,14,60,4,117,246,186,248,3,236,90,195,186,251
10 data 3,236,12,128,238,186,248,3,176,12,238,186,249,3,176,0,238,186
11 data 251,3,236,36,127,238,186,250,3,176,6,238,186,251,3,176,3,238
12 data 186,249,3,236,12,1,238,49,192,142,216,250,232,0,0,88,91,45
13 data 210,0,137,198,184,48,0,142,192,191,0,0,185,157,0,46,138,4
14 data 38,136,5,70,71,226,246,62,161,76,0,38,163,119,0,62,161,78
15 data 0,38,163,121,0,62,199,6,76,0,22,0,62,140,6,78,0,49
16 data 192,62,163,0,4,251,180,9,176,33,183,0,179,4,185,3,0,205
17 data 16,180,0,205,22,234,0,0,48,0
99 def seg=1984:a=0:for i=0 to 297:read j:poke a+i,j:next:call a
However, it is very easy to make a mistake and this work is very tedious.
Instead it's a lot better to chain-load the program using the same method from the GitHub link.
The steps are as follows, assuming you are on a Linux box:
1) Make sure that the serial port on your system is set correctly:
stty -F /dev/ttyS0 9600 raw
2) Enter and run the chain-loader in BASIC on the PS/2 system:
1 data 14,7,184,227,0,153,137,215,205,20,185,19,1,180,2,205,20,158,120,249,252,170,226,245,81,195
2 def seg=256:a=65432:for i=0 to 25:read j:poke a+i,j:next:call a
3) Send the assembled program directly through the serial port:
cat sfdboot.bin > /dev/ttyS0
4) Start the serial port floppy drive emulator with a bootable image:
./serialfd -d /dev/ttyS0 -a floppy.img
5) If everything went well, there should be three red exclamation marks on the PS/2 system, press any key to commence the booting from the emulated image.
In the case of booting MS-DOS it should look something like this:
Here is the assembly code, assembled with NASM as follows: nasm sfdboot.asm -fbin -o sfdboot.bin
org 0x0 ; Position independent.
bits 16
cpu 8086
COM1_BASE equ 0x3f8
COM1_THR equ COM1_BASE + 0 ; Transmitter Holding Buffer
COM1_RBR equ COM1_BASE + 0 ; Receiver Buffer
COM1_IER equ COM1_BASE + 1 ; Interrupt Enable Register
COM1_FCR equ COM1_BASE + 2 ; FIFO Control Register
COM1_IIR equ COM1_BASE + 2 ; Interrupt Identification Register
COM1_LCR equ COM1_BASE + 3 ; Line Control Register
COM1_LSR equ COM1_BASE + 5 ; Line Status Register
COM1_DLL equ COM1_BASE + 0 ; Divisor Latch Low Byte
COM1_DLH equ COM1_BASE + 1 ; Divisor Latch High Byte
RESIDENT_SEGMENT equ 0x0030 ; Bootstrap stack area.
section .text
start:
jmp main
resident_code_start:
; Setup ES:BX to point at bootloader address 07C0:0
mov ax, 0x07C0
mov es, ax
xor bx, bx
; Read VBR into bootloader memory area:
mov ax, 0x0201
mov cx, 0x0001
xor dx, dx
int 0x13
; Jump to bootloader:
jmp 0x0:0x7C00
int13_interrupt:
; Allow other interrupts:
sti
; Check if accessing drive 0 (A:)
; If not, then jump to original interrupt instead.
cmp dl, 0
jne original_int13
; Only operation 0x02 (Read) and 0x03 (Write) are forwarded.
; The rest are bypassed directly and returns OK.
cmp ah, 2
je _int13_interrupt_ah_ok
cmp ah, 3
jne _int13_interrupt_end
_int13_interrupt_ah_ok:
; Save registers:
push bx
push cx
push dx
; Save sectors and operation information on stack for use later:
push ax
push ax
push ax
; Register AL already set.
call com_port_send
mov al, ah
call com_port_send
mov al, cl
call com_port_send
mov al, ch
call com_port_send
mov al, dl
call com_port_send
mov al, dh
call com_port_send
; Retrieve sector information (stack AL) into DL register:
pop dx
xor dh, dh
mov ax, 512
mul dx ; DX:AX = AX * DX
mov cx, ax
; Determine receive (Read) or send (Write) from operation (stack AH):
pop ax
cmp ah, 3
je _int13_interrupt_send_loop
_int13_interrupt_recv_loop:
call com_port_recv
mov [es:bx], al
inc bx
loop _int13_interrupt_recv_loop
jmp _int13_loop_done
_int13_interrupt_send_loop:
mov al, [es:bx]
call com_port_send
inc bx
loop _int13_interrupt_send_loop
_int13_loop_done:
; Retrieve sector information (stack AL) as sectors handled:
pop ax
; Restore registers:
pop dx
pop cx
pop bx
_int13_interrupt_end:
; AL register will have same value as upon entering routine.
xor ah, ah ; Code 0 (No Error)
clc ; Clear error bit.
retf 2
original_int13:
jmp original_int13:original_int13 ; Will be overwritten runtime!
; Send contents from AL on COM1 port:
com_port_send:
push dx
mov dx, COM1_THR
out dx, al
mov dx, COM1_LSR
_com_port_send_wait:
in al, dx
and al, 0b00100000 ; Empty Transmit Holding Register
test al, al
jz _com_port_send_wait
pop dx
ret
; Return contents in AL on COM1 port:
com_port_recv:
push dx
_com_port_recv_wait:
mov dx, COM1_IIR
in al, dx
and al, 0b00001110 ; Identification
cmp al, 0b00000100 ; Enable Received Data Available Interrupt
jne _com_port_recv_wait
mov dx, COM1_RBR
in al, dx
pop dx
ret
resident_code_end:
main:
; Set Baudrate on COM1 to 9600, divisor = 12:
mov dx, COM1_LCR
in al, dx
or al, 0b10000000 ; Set Divisor Latch Access Bit (DLAB).
out dx, al
mov dx, COM1_DLL
mov al, 0xc
out dx, al
mov dx, COM1_DLH
mov al, 0
out dx, al
mov dx, COM1_LCR
in al, dx
and al, 0b01111111 ; Reset Divisor Latch Access Bit (DLAB).
out dx, al
; Disable and clear FIFO on COM1, to put it in 8250 compatibility mode:
mov dx, COM1_FCR
mov al, 0b00000110 ; Clear both FIFOs.
out dx, al
; NOTE: Not tested what happens if this is run on an actual 8250 chip...
; Set mode on COM1 to 8 data bits, no parity and 1 stop bit:
mov dx, COM1_LCR
mov al, 0b00000011 ; 8-N-1
out dx, al
; Enable interrupt bit on COM1:
mov dx, COM1_IER
in al, dx
or al, 0b00000001 ; Enable Received Data Available Interrupt
out dx, al
; Interact directly with IVT:
xor ax, ax
mov ds, ax ; Data Segment now 0000
cli ; Disable Interrupts
call get_ip
get_ip:
pop ax ; IP
pop bx ; CS
sub ax, (get_ip - resident_code_start)
mov si, ax ; "resident_code_start" now in SI.
; Copy the code to a new resident area using CS:SI -> ES:DI
mov ax, RESIDENT_SEGMENT
mov es, ax
mov di, 0
mov cx, (resident_code_end - resident_code_start)
_copy_to_resident_area:
mov byte al, [cs:si]
mov byte [es:di], al
inc si
inc di
loop _copy_to_resident_area
; Save old interrupt handler:
; ES = RESIDENT_SEGMENT
mov ax, [ds:0x4c]
mov word [es:original_int13 - resident_code_start + 1], ax
mov ax, [ds:0x4e]
mov word [es:original_int13 - resident_code_start + 3], ax
; Overwrite with new interrupt handler:
; ES = RESIDENT_SEGMENT
mov word [ds:0x4c], (int13_interrupt - resident_code_start)
mov word [ds:0x4e], es
; Zero out COM1 port address in BDA to avoid DOS interference:
; DOS can set baudrate to 2400 at startup, which will cause issues.
xor ax, ax
mov word [ds:0x400], ax
sti ; Enable Interrupts
; Indicate on screen "Ready for Loading" after key press:
mov ah, 0x9 ; Write character and attribute at cursor position.
mov al, 0x21 ; Character = '!'
mov bh, 0 ; Page Number = 0
mov bl, 0x4 ; Color = Red
mov cx, 0x3 ; Number of Times = 3
int 0x10
; Read any key press:
mov ah, 0x0 ; Read keystroke.
int 0x16
; Jump to new resident area:
jmp RESIDENT_SEGMENT:0
The code is also uploaded to the serialfd GitHub repository in case of future changes and improvements.
Serial Port Floppy Drive Emulation
While working on another project I needed to figure out a way to emulate a floppy drive. After doing some research I learned more about how the Interrupt Vector Table on PCs work and how TSR programs operate under DOS. So the result is a DOS TSR program that intercepts BIOS INT 13H calls and forwards these over the serial port to a remote Linux box that operates on a floppy disk image.
I have borrowed some code from my previous Kermit project that also uses x86 assembly with serial ports. This program also shares some of the same limitations; hard coded with baudrate 9600 on the COM1 port. The TSR has been tested on the Bochs emulator and on a real 25MHz 80486SX PC.
Here is the TSR part of the program, assembled with NASM as follows: nasm serialfd.asm -fbin -o serialfd.com
org 0x100
bits 16
cpu 8086
COM1_BASE equ 0x3f8
COM1_THR equ COM1_BASE + 0 ; Transmitter Holding Buffer
COM1_RBR equ COM1_BASE + 0 ; Receiver Buffer
COM1_IER equ COM1_BASE + 1 ; Interrupt Enable Register
COM1_FCR equ COM1_BASE + 2 ; FIFO Control Register
COM1_IIR equ COM1_BASE + 2 ; Interrupt Identification Register
COM1_LCR equ COM1_BASE + 3 ; Line Control Register
COM1_LSR equ COM1_BASE + 5 ; Line Status Register
COM1_DLL equ COM1_BASE + 0 ; Divisor Latch Low Byte
COM1_DLH equ COM1_BASE + 1 ; Divisor Latch High Byte
section .text
start:
jmp main
int13_interrupt:
; Allow other interrupts:
sti
; Check if accessing drive 0 (A:) or drive 1 (B:)
; If not, then jump to original interrupt instead.
cmp dl, 0
je _int13_interrupt_dl_ok
cmp dl, 1
jne original_int13
_int13_interrupt_dl_ok:
; Only operation 0x02 (Read) and 0x03 (Write) are forwarded.
; The rest are bypassed directly and returns OK.
cmp ah, 2
je _int13_interrupt_ah_ok
cmp ah, 3
jne _int13_interrupt_end
_int13_interrupt_ah_ok:
; Save registers:
push bx
push cx
push dx
; Save sectors and operation information on stack for use later:
push ax
push ax
push ax
; Register AL already set.
call com_port_send
mov al, ah
call com_port_send
mov al, cl
call com_port_send
mov al, ch
call com_port_send
mov al, dl
call com_port_send
mov al, dh
call com_port_send
; Retrieve sector information (stack AL) into DL register:
pop dx
xor dh, dh
mov ax, 512
mul dx ; DX:AX = AX * DX
mov cx, ax
; Determine receive (Read) or send (Write) from operation (stack AH):
pop ax
cmp ah, 3
je _int13_interrupt_send_loop
_int13_interrupt_recv_loop:
call com_port_recv
mov [es:bx], al
inc bx
loop _int13_interrupt_recv_loop
jmp _int13_loop_done
_int13_interrupt_send_loop:
mov al, [es:bx]
call com_port_send
inc bx
loop _int13_interrupt_send_loop
_int13_loop_done:
; Retrieve sector information (stack AL) as sectors handled:
pop ax
; Restore registers:
pop dx
pop cx
pop bx
_int13_interrupt_end:
; AL register will have same value as upon entering routine.
xor ah, ah ; Code 0 (No Error)
clc ; Clear error bit.
retf 2
original_int13:
jmp original_int13:original_int13 ; Will be overwritten runtime!
; Send contents from AL on COM1 port:
com_port_send:
push dx
mov dx, COM1_THR
out dx, al
mov dx, COM1_LSR
_com_port_send_wait:
in al, dx
and al, 0b00100000 ; Empty Transmit Holding Register
test al, al
jz _com_port_send_wait
pop dx
ret
; Return contents in AL on COM1 port:
com_port_recv:
push dx
_com_port_recv_wait:
mov dx, COM1_IIR
in al, dx
and al, 0b00001110 ; Identification
cmp al, 0b00000100 ; Enable Received Data Available Interrupt
jne _com_port_recv_wait
mov dx, COM1_RBR
in al, dx
pop dx
ret
; TSR end marker:
tsr_end:
main:
; NOTE: No protection to prevent TSR from being loaded twice or more!
; Set Baudrate on COM1 to 9600, divisor = 12:
mov dx, COM1_LCR
in al, dx
or al, 0b10000000 ; Set Divisor Latch Access Bit (DLAB).
out dx, al
mov dx, COM1_DLL
mov al, 0xc
out dx, al
mov dx, COM1_DLH
mov al, 0
out dx, al
mov dx, COM1_LCR
in al, dx
and al, 0b01111111 ; Reset Divisor Latch Access Bit (DLAB).
out dx, al
; Disable and clear FIFO on COM1, to put it in 8250 compatibility mode:
mov dx, COM1_FCR
mov al, 0b00000110 ; Clear both FIFOs.
out dx, al
; NOTE: Not tested what happens if this is run on an actual 8250 chip...
; Set mode on COM1 to 8 data bits, no parity and 1 stop bit:
mov dx, COM1_LCR
mov al, 0b00000011 ; 8-N-1
out dx, al
; Enable interrupt bit on COM1:
mov dx, COM1_IER
in al, dx
or al, 0b00000001 ; Enable Received Data Available Interrupt
out dx, al
; Call DOS to get original interrupt handler:
mov al, 0x13
mov ah, 0x35
int 0x21
mov word [original_int13 + 3], es
mov word [original_int13 + 1], bx
; Call DOS to set interrupt handler:
mov al, 0x13
mov ah, 0x25
; DS is already same as CS, no need to change.
mov dx, int13_interrupt
int 0x21
; Terminate and Stay Resident:
mov dx, tsr_end
shr dx, 1
shr dx, 1
shr dx, 1
shr dx, 1
add dx, 0x11 ; Add 0x1 for remainder and 0x10 for PSP.
mov ax, 0x3100
int 0x21
And here the Linux counterpart in C, just compile with GCC:
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <sys/ioctl.h>
#include <string.h>
#define REGISTER_AL 0
#define REGISTER_AH 1
#define REGISTER_CL 2
#define REGISTER_CH 3
#define REGISTER_DL 4
#define REGISTER_DH 5
#define SECTOR_SIZE 512
#define HEADS_PER_CYLINDER_DEFAULT 2
#define OPERATION_READ_DISK_SECTORS 0x02
#define OPERATION_WRITE_DISK_SECTORS 0x03
static uint16_t get_sectors_per_track(FILE *fh)
{
uint16_t spt;
fseek(fh, 24, SEEK_SET); /* Offset in Volume Boot Record. */
if (fread(&spt, sizeof(uint16_t), 1, fh) != 1) {
return 0; /* Error */
}
/* Currently handling 720K and 1.44M floppies. */
if (spt == 9 || spt == 18) {
return spt; /* Valid */
}
return 0; /* Invalid */
}
static void display_help(char *progname)
{
fprintf(stderr, "Usage: %s <options>\n", progname);
fprintf(stderr, "Options:\n"
" -h Display this help and exit.\n"
" -d DEVICE Use TTY DEVICE.\n"
" -a IMAGE Floppy IMAGE for A:\n"
" -b IMAGE Floppy IMAGE for B:\n"
" -H HPC Force HPC heads per cylinder.\n"
" -S SPT Force SPT sectors per track.\n"
" -v Verbose debugging output.\n"
"\n");
}
int main(int argc, char *argv[])
{
int result = EXIT_SUCCESS;
int i, c, arg;
int cylinder, sector, lba;
struct termios attr;
unsigned char registers[6];
int debug_output = 0;
char *tty_device = NULL;
int tty_fd = -1;
FILE *fh;
char *floppy_a_image = NULL;
char *floppy_b_image = NULL;
FILE *floppy_a_fh = NULL;
FILE *floppy_b_fh = NULL;
uint16_t floppy_a_spt = 0;
uint16_t floppy_b_spt = 0;
int spt = 0;
int hpc = HEADS_PER_CYLINDER_DEFAULT;
char *operation;
while ((c = getopt(argc, argv, "hd:a:b:H:S:v")) != -1) {
switch (c) {
case 'h':
display_help(argv[0]);
return EXIT_SUCCESS;
case 'd':
tty_device = optarg;
break;
case 'a':
floppy_a_image = optarg;
break;
case 'b':
floppy_b_image = optarg;
break;
case 'H':
hpc = atoi(optarg);
break;
case 'S':
spt = atoi(optarg);
break;
case 'v':
debug_output = 1;
break;
case '?':
default:
display_help(argv[0]);
return EXIT_FAILURE;
}
}
if (tty_device == NULL) {
fprintf(stderr, "Please specify a TTY!\n");
display_help(argv[0]);
return EXIT_FAILURE;
}
if (floppy_a_image == NULL && floppy_b_image == NULL) {
fprintf(stderr, "Please specify at least one floppy image!\n");
display_help(argv[0]);
return EXIT_FAILURE;
}
if (hpc == 0) {
fprintf(stderr, "Invalid heads per cylinder!\n");
return EXIT_FAILURE;
}
/* Open serial TTY device. */
tty_fd = open(tty_device, O_RDWR | O_NOCTTY);
if (tty_fd == -1) {
fprintf(stderr, "open() on TTY device failed with errno: %d\n", errno);
return EXIT_FAILURE;
}
/* Set TTY into a very raw mode. */
memset(&attr, 0, sizeof(struct termios));
attr.c_cflag = B9600 | CS8 | CLOCAL | CREAD;
attr.c_cc[VMIN] = 1;
if (tcsetattr(tty_fd, TCSANOW, &attr) == -1) {
fprintf(stderr, "tcgetattr() on TTY device failed with errno: %d\n", errno);
close(tty_fd);
return EXIT_FAILURE;
}
/* Make sure TTY "Clear To Send" signal is set. */
arg = TIOCM_CTS;
if (ioctl(tty_fd, TIOCMBIS, &arg) == -1) {
fprintf(stderr, "ioctl() on TTY device failed with errno: %d\n", errno);
close(tty_fd);
return EXIT_FAILURE;
}
/* Get information about floppy A: */
if (floppy_a_image != NULL) {
floppy_a_fh = fopen(floppy_a_image, "r+b");
if (floppy_a_fh == NULL) {
fprintf(stderr, "fopen() for floppy A: failed with errno: %d\n", errno);
result = EXIT_FAILURE;
goto main_end;
}
if (spt == 0) {
floppy_a_spt = get_sectors_per_track(floppy_a_fh);
} else {
floppy_a_spt = spt;
}
if (floppy_a_spt == 0) {
fprintf(stderr, "Invalid sectors per track for floppy A:\n");
result = EXIT_FAILURE;
goto main_end;
}
}
/* Get information about floppy B: */
if (floppy_b_image != NULL) {
floppy_b_fh = fopen(floppy_b_image, "r+b");
if (floppy_b_fh == NULL) {
fprintf(stderr, "fopen() for floppy B: failed with errno: %d\n", errno);
result = EXIT_FAILURE;
goto main_end;
}
if (spt == 0) {
floppy_b_spt = get_sectors_per_track(floppy_b_fh);
} else {
floppy_b_spt = spt;
}
if (floppy_b_spt == 0) {
fprintf(stderr, "Invalid sectors per track for floppy B:\n");
result = EXIT_FAILURE;
goto main_end;
}
}
/* Process input and output. */
while (1) {
for (i = 0; i < 6; i++) {
if (read(tty_fd, ®isters[i], sizeof(unsigned char)) != 1) {
fprintf(stderr, "read() failed with errno: %d\n", errno);
result = EXIT_FAILURE;
goto main_end;
}
}
if (debug_output) {
fprintf(stderr, "AL: 0x%02x\n", registers[REGISTER_AL]);
fprintf(stderr, "AH: 0x%02x\n", registers[REGISTER_AH]);
fprintf(stderr, "CL: 0x%02x\n", registers[REGISTER_CL]);
fprintf(stderr, "CH: 0x%02x\n", registers[REGISTER_CH]);
fprintf(stderr, "DL: 0x%02x\n", registers[REGISTER_DL]);
fprintf(stderr, "DH: 0x%02x\n", registers[REGISTER_DH]);
}
if (registers[REGISTER_DL] == 0x00) {
spt = floppy_a_spt;
fh = floppy_a_fh;
} else if (registers[REGISTER_DL] == 0x01) {
spt = floppy_b_spt;
fh = floppy_b_fh;
} else {
fprintf(stderr, "Error: Invalid drive number: %02x\n",
registers[REGISTER_DL]);
result = EXIT_FAILURE;
goto main_end;
}
/* CX = ---CH--- ---CL---
* cylinder : 76543210 98
* sector : 543210
* LBA = ( ( cylinder * HPC + head ) * SPT ) + sector - 1
*/
cylinder = ((registers[REGISTER_CL] & 0xc0) << 2)
+ registers[REGISTER_CH];
sector = registers[REGISTER_CL] & 0x3f;
lba = ((cylinder * hpc + registers[REGISTER_DH]) * spt) + sector - 1;
if (debug_output) {
fprintf(stderr, "Cylinder: %d\n", cylinder);
fprintf(stderr, "Sector : %d\n", sector);
fprintf(stderr, "SPT : %d\n", spt);
fprintf(stderr, "HPC : %d\n", hpc);
fprintf(stderr, "LBA : %d\n", lba);
fprintf(stderr, "Offset : 0x%x\n", lba * SECTOR_SIZE);
} else {
switch (registers[REGISTER_AH]) {
case OPERATION_READ_DISK_SECTORS:
operation = "Read";
break;
case OPERATION_WRITE_DISK_SECTORS:
operation = "Write";
break;
default:
operation = "Unknown";
break;
}
fprintf(stderr, "%s %c: sector=%d, cylinder=%d count=%d\n",
operation, (registers[REGISTER_DL] == 0x00) ? 'A' : 'B',
sector, cylinder, registers[REGISTER_AL]);
}
if (fh != NULL) {
if (fseek(fh, lba * SECTOR_SIZE, SEEK_SET) == -1) {
fprintf(stderr, "fseek() failed with errno: %d\n", errno);
result = EXIT_FAILURE;
goto main_end;
}
}
switch (registers[REGISTER_AH]) {
case OPERATION_READ_DISK_SECTORS:
if (debug_output) {
fprintf(stderr, "READ SECTOR DATA:\n");
}
for (i = 0; i < (SECTOR_SIZE * registers[REGISTER_AL]); i++) {
if (fh != NULL) {
c = fgetc(fh);
} else {
c = 0xFF; /* Dummy data if image is not loaded. */
}
if (debug_output) {
fprintf(stderr, "%02x ", c);
if (i % 16 == 15) {
fprintf(stderr, "\n");
}
}
write(tty_fd, &c, sizeof(unsigned char));
}
break;
case OPERATION_WRITE_DISK_SECTORS:
if (debug_output) {
fprintf(stderr, "WRITE SECTOR DATA:\n");
}
for (i = 0; i < (SECTOR_SIZE * registers[REGISTER_AL]); i++) {
read(tty_fd, &c, sizeof(unsigned char));
if (fh != NULL) {
fputc(c, fh);
}
if (debug_output) {
fprintf(stderr, "%02x ", c);
if (i % 16 == 15) {
fprintf(stderr, "\n");
}
}
}
if (fh != NULL) {
fflush(fh);
}
break;
default:
fprintf(stderr, "Error: Unhandled operation: %02x\n",
registers[REGISTER_AH]);
result = EXIT_FAILURE;
goto main_end;
}
}
main_end:
if (tty_fd != -1) close(tty_fd);
if (floppy_a_fh != NULL) fclose(floppy_a_fh);
if (floppy_b_fh != NULL) fclose(floppy_b_fh);
return result;
}
I have also uploaded the code to GitHub in case case of further improvements in the future.
Kermit in x86 Assembly
This is kind of a follow up to my other project on file transfers in DOS. I have made a huge improvement by implementing the Kermit Protocol in 16-bit x86 assembly language. Instead of relying on the horrible BIOS service routines, this program interfaces directly to the 8250/16550 UART chip on the PC.
The purpose of this program is bootstrapping, so it has several limitations. It is based loosely on the "Baby Kermit" BASIC program that can be found in the official Kermit manuals. It's hard coded to run at 9600 baud with 8-N-1 parameters on the COM1 port. Both sending and receiving is performed by hogging the CPU and busy-waiting. I recommend to use this program as a means to transfer the real full-feature MS-DOS Kermit.
Apart from testing the program in both the DOSBox and Bochs emulators, I have also tried it on two real machines. On a 8MHz 8088 XT-class machine, it gets some transmission errors, but those are corrected. On a 25MHz 80486SX it runs fine without any errors.
I have uploaded the code to GitHub in case of further improvements, by me or anyone else. But here is the first version, assembled with NASM as follows: nasm kermit.asm -fbin -o kermit.com
org 0x100
bits 16
cpu 8086
COM1_BASE equ 0x3f8
COM1_THR equ COM1_BASE + 0 ; Transmitter Holding Buffer
COM1_RBR equ COM1_BASE + 0 ; Receiver Buffer
COM1_IER equ COM1_BASE + 1 ; Interrupt Enable Register
COM1_FCR equ COM1_BASE + 2 ; FIFO Control Register
COM1_IIR equ COM1_BASE + 2 ; Interrupt Identification Register
COM1_LCR equ COM1_BASE + 3 ; Line Control Register
COM1_LSR equ COM1_BASE + 5 ; Line Status Register
COM1_DLL equ COM1_BASE + 0 ; Divisor Latch Low Byte
COM1_DLH equ COM1_BASE + 1 ; Divisor Latch High Byte
RECV_BUFFER_SIZE equ 100 ; As per Kermit documentation.
SEND_BUFFER_SIZE equ 16 ; No packets sent from this program exceed this.
PACKET_DATA_SIZE equ 94 ; Receive buffer size - 6 fields/terminator.
section .text
start:
; Set Baudrate on COM1 to 9600, divisor = 12:
mov dx, COM1_LCR
in al, dx
or al, 0b10000000 ; Set Divisor Latch Access Bit (DLAB)
out dx, al
mov dx, COM1_DLL
mov al, 0xc
out dx, al
mov dx, COM1_DLH
mov al, 0
out dx, al
mov dx, COM1_LCR
in al, dx
and al, 0b01111111 ; Reset Divisor Latch Access Bit (DLAB)
out dx, al
; Disable and clear FIFO on COM1, to put it in 8250 compatibility mode:
mov dx, COM1_FCR
mov al, 0b00000110 ; Clear both FIFOs.
out dx, al
; Set mode on COM1 to 8 data bits, no parity and 1 stop bit:
mov dx, COM1_LCR
mov al, 0b00000011 ; 8-N-1
out dx, al
; Enable interrupt bit on COM1:
mov dx, COM1_IER
in al, dx
or al, 0b00000001 ; Enable Received Data Available Interrupt
out dx, al
; Initialize sequence number:
mov byte [send_seq_no], 0
; Initialize retransmit message in send buffer:
mov byte [send_buffer], 0x01 ; 'MARK' Start marker (Ctrl-A)
mov byte [send_buffer + 1], 35 ; 'LEN' Packet length of 3 (+ 32)
mov byte [send_buffer + 2], 32 ; 'SEQ' Sequence number 0 (+ 32)
mov byte [send_buffer + 3], 'N' ; 'TYPE' Packet type 'N' meaning NAK
mov byte [send_buffer + 4], 0x33 ; 'CHECK' Checksum 0x13 (+ 32)
mov byte [send_buffer + 5], 0x13 ; Terminator (Carriage Return)
mov word [send_buffer_index], 6
; Get Send Initialization packet, exchange parameters...
mov dx, message_waiting
call print_string
call get_valid_packet
mov byte al, [packet_type]
cmp al, 'S' ; 'S' = Send Initiation
je _handle_s_packet
; Simplified version of error message: "<?> Packet in S State"
mov byte [packet_data], al
mov byte [packet_data + 1], 'S'
mov byte [packet_type], 'E' ; 'E' = Error
mov word [packet_data_len], 2
call send_packet
jmp _main_end
_handle_s_packet:
; Override local EOL marker from sender if available:
mov byte al, [packet_data_len]
cmp al, 4
jb _acknowledge_s_packet
mov byte bl, [packet_data + 4] ; 'EOL'
sub bl, 32
mov [eol_marker], bl
; Override local CTL marker from sender if available:
cmp al, 5
jb _acknowledge_s_packet
mov byte bl, [packet_data + 5] ; 'QCTL'
mov [ctl_marker], bl
_acknowledge_s_packet:
mov byte [packet_type], 'Y' ; 'Y' = Acknowledgement (ACK)
mov byte [packet_data], 72 ; 'MAXL'
mov byte [packet_data + 1], 42 ; 'TIME'
mov byte [packet_data + 2], 32 ; 'NPAD'
mov byte [packet_data + 3], 64 ; 'PADC'
mov byte [packet_data + 4], 45 ; 'EOL' = 0x0d (+ 32)
mov byte [packet_data + 5], 35 ; 'QCTL' = '#'
mov byte [packet_data + 6], 'N' ; 'QBIN' = 'N' = Will not do 8-bit quoting.
mov byte [packet_data + 7], '1' ; 'CHKT' = '1' = Single character checksum.
mov word [packet_data_len], 8
call send_packet
_wait_for_file_header_packet:
; Get a File Header packet. If a B packet comes, we're all done:
call get_valid_packet
mov byte al, [packet_type]
cmp al, 'B' ; 'B' = Break transmission
je _handle_b_packet
cmp al, 'F' ; 'F' = File Header
je _handle_f_packet
; Simplified version of error message: "<?> Packet in F State"
mov byte [packet_data], al
mov byte [packet_data + 1], 'F'
mov byte [packet_type], 'E' ; 'E' = Error
mov word [packet_data_len], 2
call send_packet
jmp _main_end
_handle_b_packet:
call send_acknowledgement_packet
jmp _main_end
_handle_f_packet:
mov dx, message_receiving
call print_string
; Dollar terminate the received filename:
mov word di, [packet_data_len]
mov byte [packet_data + di], '$'
mov dx, packet_data
call print_string
; Zero terminate the received filename:
mov byte [packet_data + di], 0
; Call DOS to create new file and handle.
mov ah, 0x3c
mov cx, 0 ; Standard attributes.
; DX already containing pointer to packet data.
int 0x21
jc _handle_f_packet_error
mov [file_handle], ax
call send_acknowledgement_packet
_wait_for_data_packet:
; Get Data packets. If a Z packet comes, the file is complete:
call get_valid_packet
mov byte al, [packet_type]
cmp al, 'Z' ; 'Z' = End of file
je _handle_z_packet
cmp al, 'D' ; 'D' = Data Packet
je _handle_d_packet
; Simplified version of error message: "<?> Packet in D State"
mov byte [packet_data], al
mov byte [packet_data + 1], 'D'
mov byte [packet_type], 'E' ; 'E' = Error
mov word [packet_data_len], 2
call send_packet
jmp _main_end
_handle_z_packet:
; Call DOS to close file handle.
mov ah, 0x3e
mov bx, [file_handle]
int 0x21
call send_acknowledgement_packet
mov dx, message_ok
call print_string
jmp _wait_for_file_header_packet
_handle_d_packet:
; Call DOS to write to file.
mov ah, 0x40
mov word bx, [file_handle]
mov word cx, [packet_data_len]
mov dx, packet_data
int 0x21
jc _handle_d_packet_error
call send_acknowledgement_packet
jmp _wait_for_data_packet
_handle_f_packet_error:
; Send error code 'C', since new file could not be created.
mov byte [packet_data], 'C'
mov byte [packet_type], 'E' ; 'E' = Error
mov word [packet_data_len], 1
call send_packet
jmp _main_end
_handle_d_packet_error:
; Send error code 'W', since new file could not be written to.
mov byte [packet_data], 'W'
mov byte [packet_type], 'E' ; 'E' = Error
mov word [packet_data_len], 1
call send_packet
jmp _main_end
_main_end:
mov dx, message_done
call print_string
; Disable interrupt bit on COM1:
mov dx, COM1_IER
in al, dx
and al, 0b11111110 ; Disable Received Data Available Interrupt
out dx, al
; Exit to DOS.
mov ah, 0x4c
int 0x21
; PROCEDURE: get_valid_packet
;
; INPUT:
; N/A
;
; OUTPUT:
; ds:[packet_type]
; ds:[packet_data]
; ds:[packet_data_len]
;
get_valid_packet:
push ax
push bx
push cx
; Try to get a valid packet with the desired sequence number.
mov cx, 5 ; Retry maximum 5 times.
_get_valid_packet_loop:
call recv_packet
mov byte al, [recv_seq_no]
mov byte bl, [send_seq_no]
cmp al, bl
jne _get_valid_packet_resend
mov byte al, [packet_type]
cmp al, 'Q' ; 'Q' = Block check error
je _get_valid_packet_resend
jmp _get_valid_packet_return ; Got a valid packet.
_get_valid_packet_resend:
call com_port_send ; Contains a retransmit message in send buffer already.
push dx
mov dl, '%' ; Indicate retry.
call print_character
pop dx
loop _get_valid_packet_loop ; Until CX = 0
mov byte [packet_type], 'T' ; 'T' = Timeout
_get_valid_packet_return:
pop cx
pop bx
pop ax
ret
; PROCEDURE: send_acknowledgement_packet
;
; INPUT:
; N/A
;
; OUTPUT:
; N/A
;
send_acknowledgement_packet:
mov byte [packet_type], 'Y' ; 'Y' = Acknowledgement (ACK)
mov word [packet_data_len], 0
call send_packet
ret
; PROCEDURE: send_packet
;
; INPUT:
; ds:[packet_type]
; ds:[packet_data]
; ds:[packet_data_len]
;
; OUTPUT:
; N/A
;
send_packet:
push ax
push bx
push cx
push di
push si
mov di, send_buffer
mov byte [di], 0x01
inc di
mov word ax, [packet_data_len]
add al, 35 ; 32 + 3 bytes for 'SEQ', 'TYPE' & 'CHECK'
mov bl, al ; Checksum = LEN
mov byte [di], al
inc di
mov byte al, [send_seq_no]
add al, 32
add bl, al ; Checksum += SEQ
mov byte [di], al
inc di
mov byte al, [packet_type]
add bl, al ; Checksum += TYPE
mov byte [di], al
inc di
mov si, packet_data
mov word cx, [packet_data_len]
test cx, cx
jz _send_packet_empty
_send_packet_loop:
mov al, [si]
mov [di], al
add bl, al ; Checksum += DATA
inc di
inc si
loop _send_packet_loop ; Until CX = 0
_send_packet_empty:
; Calculate checksum:
mov cl, bl
and cl, 192
shr cl, 1 ; 8086 is limited to one shift at a time.
shr cl, 1
shr cl, 1
shr cl, 1
shr cl, 1
shr cl, 1
add cl, bl
and cl, 63
add cl, 32
mov byte [di], cl
inc di
mov byte al, [eol_marker]
mov byte [di], al
mov word ax, [packet_data_len]
add ax, 6 ; Add 'MARK', 'LEN', 'SEQ', 'TYPE' 'CHECK' and terminator.
mov word [send_buffer_index], ax
call com_port_send
; Increment packet sequence number:
inc byte [send_seq_no]
and byte [send_seq_no], 63 ; Always reduce to 6 bits.
push dx
mov dl, '.'; Indicate ACK sent.
call print_character
pop dx
pop si
pop di
pop cx
pop bx
pop ax
ret
; PROCEDURE: com_port_send
;
; INPUT:
; ds:[send_buffer]
; ds:[send_buffer_index]
;
; OUTPUT:
; N/A
;
com_port_send:
push ax
push cx
push dx
push si
mov si, 0
mov word cx, [send_buffer_index]
_com_port_send_byte:
mov dx, COM1_THR
mov byte al, [send_buffer + si]
out dx, al
mov dx, COM1_LSR
_com_port_send_wait:
in al, dx
and al, 0b00100000 ; Empty Transmit Holding Register
test al, al
jz _com_port_send_wait ; Busy wait...
inc si
loop _com_port_send_byte ; Until CX = 0
pop si
pop dx
pop cx
pop ax
ret
; PROCEDURE: recv_packet
;
; INPUT:
; N/A
;
; OUTPUT:
; ds:[packet_type]
; ds:[packet_data]
; ds:[packet_data_len]
; ds:[recv_seq_no]
;
recv_packet:
push ax
push bx
push cx
push dx
push di
push si
call com_port_recv
; Look for 'MARK' start marker 0x01 (Ctrl-A) in buffer:
mov si, -1
_recv_packet_look_for_marker:
inc si
mov ax, [recv_buffer_index]
cmp si, ax
jge _recv_packet_fail ; Reached end of buffer.
mov byte al, [recv_buffer + si]
cmp al, 0x01 ; (Ctrl-A)
jne _recv_packet_look_for_marker
; Start position now in SI register.
; Copy initial packet fields:
; * Using AL for data.
; * Using BL for checksum.
; * Using CX for packet length.
inc si
xor cx, cx
mov byte cl, [recv_buffer + si] ; Packet 'LEN' field.
mov bl, cl ; Checksum = LEN
sub cx, 35 ; 32 + 3 bytes for 'SEQ', 'TYPE' & 'CHECK'
inc si
mov byte al, [recv_buffer + si] ; Packet 'SEQ' field.
add bl, al ; Checksum += SEQ
sub al, 32
mov byte [recv_seq_no], al
inc si
mov byte al, [recv_buffer + si] ; Packet 'TYPE' field.
add bl, al ; Checksum += TYPE
mov byte [packet_type], al
inc si
; Packet length now in CX register.
; Checksum now in BL register.
; Start of data position now in SI register.
mov word [packet_data_len], cx
test cx, cx
jz _recv_packet_checksum ; Zero size packet, skip decoding/copying.
; Copy packet data:
; * Using AL for data.
; * Using BL for checksum.
; * Using CX for packet length.
; * Using DL for comparisons and temporary storage.
; * Using DH for decode flag.
xor dh, dh
mov di, packet_data
_recv_packet_copy:
mov byte al, [recv_buffer + si] ; Packet 'DATA' field.
add bl, al ; Checksum += DATA
mov byte dl, [packet_type]
cmp dl, 'S' ; 'S' = Send Initiation
jne _recv_packet_decode ; Type 'S' packets shall not be decoded!
mov [di], al ; Copy un-decoded.
jmp _recv_packet_increment
_recv_packet_decode:
cmp dh, 0
jne _recv_packet_decode_flag_not_set_1
mov byte dl, [ctl_marker]
cmp dl, al
jne _recv_packet_decode_flag_not_set_1
mov dh, 1
dec byte [packet_data_len] ; Decoding reduces resulting packet size.
jmp _recv_packet_increment_source_only
_recv_packet_decode_flag_not_set_1:
cmp dh, 1
jne _recv_packet_decode_flag_not_set_2
xor dh, dh
mov dl, al
and dl, 127
cmp dl, 62
jng _recv_packet_decode_flag_not_set_2
cmp dl, 96
jg _recv_packet_decode_flag_not_set_2
xor al, 64
_recv_packet_decode_flag_not_set_2:
mov [di], al
_recv_packet_increment:
inc di
_recv_packet_increment_source_only:
inc si
loop _recv_packet_copy ; Until CX = 0
_recv_packet_checksum:
; Calculate and check checksum:
mov dl, bl
and dl, 192
shr dl, 1 ; 8086 is limited to one shift at a time.
shr dl, 1
shr dl, 1
shr dl, 1
shr dl, 1
shr dl, 1
add dl, bl
and dl, 63
mov byte al, [recv_buffer + si] ; Packet 'CHECK' field.
sub al, 32
cmp al, dl
jne _recv_packet_fail
; All OK!
jmp _recv_packet_ok
_recv_packet_fail:
mov byte [packet_type], 'Q' ; 'Q' = Block check error
_recv_packet_ok:
pop si
pop di
pop dx
pop cx
pop bx
pop ax
ret
; PROCEDURE: com_port_recv
;
; INPUT:
; N/A
;
; OUTPUT:
; ds:[recv_buffer]
; ds:[recv_buffer_index]
;
com_port_recv:
push ax
push dx
push di
mov di, 0
_com_port_recv_byte:
mov dx, COM1_IIR
_com_port_recv_wait:
in al, dx
and al, 0b00001110 ; Identification
cmp al, 0b00000100 ; Enable Received Data Available Interrupt
jne _com_port_recv_wait ; Busy wait...
mov dx, COM1_RBR
in al, dx
cmp di, RECV_BUFFER_SIZE
jb _com_port_recv_copy
mov di, 0 ; Reset and wrap to prevent overflow.
_com_port_recv_copy:
mov byte [recv_buffer + di], al
inc di
; Keep reading until a terminator 0x0d (Carriage Return) arrives:
cmp al, 0x0d
jne _com_port_recv_byte
mov word [recv_buffer_index], di
pop di
pop dx
pop ax
ret
; PROCEDURE: print_character
;
; INPUT:
; dl
;
; OUTPUT:
; N/A
;
print_character:
push ax
push dx
; Call DOS to display character:
mov ah, 0x2
; DL set by caller...
int 0x21
pop dx
pop ax
ret
; PROCEDURE: print_string
;
; INPUT:
; dx
;
; OUTPUT:
; N/A
;
print_string:
push ax
; Call DOS to display string:
mov ah, 0x9
; DS is already same as CS, no need to change.
; DX set by caller...
int 0x21
pop ax
ret
section .data:
recv_buffer_index:
dw 0 ; 16-bit word due to SI/DI registers.
recv_buffer:
times RECV_BUFFER_SIZE db 0
send_buffer_index:
dw 0 ; 16-bit word due to SI/DI registers.
send_buffer:
times SEND_BUFFER_SIZE db 0
send_seq_no:
db 0
recv_seq_no:
db 0
packet_type:
db 0
packet_data_len:
dw 0 ; 16-bit word due to SI/DI registers.
packet_data:
times PACKET_DATA_SIZE db 0
ctl_marker:
db '#' ; Default
eol_marker:
db 0x0d ; Default
file_handle:
dw 0
message_waiting:
db "Waiting...", 0x0d, 0x0a, "$"
message_receiving:
db "Receiving: $"
message_ok:
db "(OK)", 0x0d, 0x0a, "$"
message_done:
db "(DONE)", 0x0d, 0x0a, "$"
For convenience, here is an example of commands to send a file with C-Kermit on Linux:
set modem type none
set line /dev/ttyUSB0
set carrier-watch off
set speed 9600
set flow none
set parity none
set stop-bits 1
send <filename>
M.I.A. in Wine
M.I.A.: Missing In Action is a relatively unknown game that came out for Windows back in 1998. I got the game back then in my childhood as part of some bundle with a new computer. I do remember the game being fun, but I had issues getting it to run later on because it will only install on Windows 98. Fast forward some 20 years, Wine has now become a better Windows than Windows on Linux in many aspects, especially running older games.
I have been using Wine version 4.0.2 for these experiments.
Using some tricks I finally got to run and play this on Linux! In order to get there I had do spend some time with both Winedbg and OllyDbg debuggers to figure out what the game tried to do and failed on.
The first problem was the detection of the CDs, which I figured out it does by calling GetVolumeInformationA() and looking at the volume label. This is fixed by creating a ".windows-label" file in the emulated CD drive with the correct label.
The second problem was getting the CD audio to work correctly. Apart from having to fake this somehow, the game uses the ancient Media Control Interface which still have some missing features (bugs?) in Wine at the time of writing. Maybe this will be fixed in an upcoming version, but I had no time to wait for that. The root of the problem is that Wine returns the code (as string) "1088" instead of the string "audio" when the game asks what type of track is on the CD. The quickest way to fix this is to simply patch the game binary to look for that other string.
To actually play the CD audio without the CDs I figured out it was easiest to hack the Wine "mcicda.dll" library and make it call MPlayer to play the tracks as .FLAC files. This is done in MPlayer's FIFO mode to avoid blocking anything.
A third problem is that the in-game video cutscenes, using Smacker Video Technology still does not play correctly in Wine. The symptom is that the video may play for some seconds, but then just hangs. Since it's possible to bypass this by hitting Escape, I have simply ignored this for now.
Anyway, the common steps to install and run are as follows:
1) Create a new directory to store a Wine prefix for M.I.A.:
mkdir -p ~/opt/mia
2) Run winecfg on the prefix, in 32-bit mode, and set it has "Windows 98":
WINEARCH=win32 WINEPREFIX=~/opt/mia winecfg
3) Create two directories for each M.I.A. CD in the prefix:
mkdir ~/opt/mia/cd1
mkdir ~/opt/mia/cd2
4) Copy the CD contents into the respective directories.
Either directly from the CDs or ISO images mounted as loopback devices.
5) Create fake volume labels for each CD, as needed by the game:
echo "MIA_VOL1" > ~/opt/mia/cd1/.windows-label
echo "MIA_VOL2" > ~/opt/mia/cd2/.windows-label
6) Create a symbolic link kalled "drive_d" pointing to "cd1"
ln -s "cd1" ~/opt/mia/drive_d
7) Run winecfg again to map D: to the newly created "drive_d" directory.
Also set the type as "CD-ROM".
WINEARCH=win32 WINEPREFIX=~/opt/mia winecfg
8) Allow low memory to be mapped, since it is needed by M.I.A. installer.
sudo sysctl vm.mmap_min_addr=0
9) Start the M.I.A. installation through Wine,
WINEARCH=win32 WINEPREFIX=~/opt/mia wine ~/opt/mia/drive_d/mia.exe
10) When prompted for installation of installation type...
Select "Leave ground textures on CD".
This is needed because the installer has issues finding CD #2.
11) Run the following script to easily start the game:
#!/bin/sh
export WINEPREFIX=~/opt/mia
sudo sysctl vm.mmap_min_addr=0 # Wine needs to be allowed to map low memory.
CD_NO=0
while [ "$CD_NO" != "1" ] && [ "$CD_NO" != "2" ]; do
read -p "CD Number? (1 or 2) " CD_NO
done
rm -f "${WINEPREFIX}/drive_d"
ln -s "cd$CD_NO" "${WINEPREFIX}/drive_d"
(cd "${WINEPREFIX}/drive_c/MIA" && WINEARCH=win32 wine miarel.exe -avhpd)
If you also want the in-game music, some additional steps are required:
12) Assuming all tracks are ripped from the CD's in FLAC format.
4 audio tracks from CD #1 named from "track02.flac" to "track05.flac".
5 audio tracks from CD #2 mamed from "track02.flac" to "track06.flac".
Copy .flac files into the root of each respective directory "cd1" and "cd2".
13) Patch the "mcicda.dll" file in ~/opt/mia/drive_c/windows/system32/
14) Patch the "miarel.exe" file in ~/opt/mia/drive_c/MIA/
15) Run the following modified script to start the game:
#!/bin/sh
export WINEPREFIX=~/opt/mia
MPLAYER_FIFO=/tmp/mplayer.fifo # Do not change, hardcoded in patched mcicda.dll
sudo sysctl vm.mmap_min_addr=0 # Wine needs to be allowed to map low memory.
CD_NO=0
while [ "$CD_NO" != "1" ] && [ "$CD_NO" != "2" ]; do
read -p "CD Number? (1 or 2) " CD_NO
done
rm -f "${WINEPREFIX}/drive_d"
ln -s "cd$CD_NO" "${WINEPREFIX}/drive_d"
if [ ! -p "$MPLAYER_FIFO" ]; then
mkfifo "$MPLAYER_FIFO"
fi
cd "${WINEPREFIX}/drive_d"
mplayer -idle -slave -input file=$MPLAYER_FIFO 1&>/dev/null &
MPLAYER_PID=$!
cd -
(cd "${WINEPREFIX}/drive_c/MIA" && WINEARCH=win32 wine miarel.exe -avhpd)
kill $MPLAYER_PID
rm -f "$MPLAYER_FIFO"
To patch "miarel.exe", open it in a hex-editor and go to offset 0x1427c4. At this location the string "audio" should be present. Replace this with 0x31 0x30 0x38 0x38 0x00 which represents the string "1088" with an additional NULL terminator.
Patching "mcicda.dll" is more complicated as it requires a rebuild of Wine. Get the Wine source code and apply the following source code patch to "./dlls/mcicda/mcicda.c":
--- mcicda.c.orig 2020-05-13 17:55:02.433346437 +0200
+++ mcicda.c 2020-05-13 17:54:53.230346338 +0200
@@ -25,6 +25,12 @@
#include <stdio.h>
#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <limits.h>
+
#define WIN32_NO_STATUS
#include "windef.h"
#include "winbase.h"
@@ -79,10 +85,72 @@
typedef HRESULT(WINAPI*LPDIRECTSOUNDCREATE)(LPCGUID,LPDIRECTSOUND*,LPUNKNOWN);
static LPDIRECTSOUNDCREATE pDirectSoundCreate;
+static void mplayer_command(const char *command)
+{
+ int fd, written;
+
+ fd = open("/tmp/mplayer.fifo", O_NONBLOCK | O_WRONLY);
+ if (fd == -1) {
+ TRACE("No pipe\n");
+ return;
+ }
+
+ written = write(fd, command, strlen(command));
+ if (written <= 0) {
+ TRACE("Write failed\n");
+ }
+
+ close(fd);
+}
+
static BOOL device_io(HANDLE dev, DWORD code, void *inbuffer, DWORD insize, void *outbuffer, DWORD outsize, DWORD *retsize, OVERLAPPED *overlapped)
{
const char *str;
- BOOL ret = DeviceIoControl(dev, code, inbuffer, insize, outbuffer, outsize, retsize, overlapped);
+// BOOL ret = DeviceIoControl(dev, code, inbuffer, insize, outbuffer, outsize, retsize, overlapped);
+
+ int i;
+ BOOL ret = TRUE;
+ CDROM_TOC *toc;
+
+ *retsize = 0;
+
+ switch (code) {
+ case IOCTL_CDROM_READ_TOC:
+ toc = (CDROM_TOC *)outbuffer;
+
+ toc->FirstTrack = 1;
+ toc->LastTrack = 6;
+
+ // Set up first track as data track.
+ toc->TrackData[0].TrackNumber = 1;
+ toc->TrackData[0].Control = 0x4;
+ toc->TrackData[0].Address[1] = 0;
+ toc->TrackData[0].Address[2] = 0;
+ toc->TrackData[0].Address[3] = 0;
+
+ // Set up remaining tracks as dummy audio tracks.
+ for (i = 1; i < toc->LastTrack; i++) {
+ toc->TrackData[i].TrackNumber = i + 1;
+ toc->TrackData[i].Control = 0;
+ toc->TrackData[i].Address[1] = i;
+ toc->TrackData[i].Address[2] = 0;
+ toc->TrackData[i].Address[3] = 0;
+ }
+
+ *retsize = CDROM_TOC_SIZE;
+ break;
+
+ case IOCTL_CDROM_STOP_AUDIO:
+ mplayer_command("stop\n");
+ break;
+
+ case IOCTL_CDROM_PAUSE_AUDIO:
+ mplayer_command("stop\n");
+ break;
+
+ default:
+ break;
+ }
#define XX(x) case (x): str = #x; break
switch (code)
@@ -906,6 +974,9 @@
SUB_Q_CHANNEL_DATA data;
CDROM_TOC toc;
+ int track_no;
+ char command[PATH_MAX];
+
TRACE("(%04X, %08X, %p);\n", wDevID, dwFlags, lpParms);
if (lpParms == NULL)
@@ -914,6 +985,20 @@
if (wmcda == NULL)
return MCIERR_INVALID_DEVICE_ID;
+ // HIJACK START
+
+ mplayer_command("stop\n");
+
+ track_no = MCI_TMSF_TRACK(lpParms->dwFrom);
+ TRACE("Track no: %d\n", track_no);
+
+ snprintf(command, PATH_MAX, "loadfile track%02d.flac\n", track_no);
+ mplayer_command(command);
+
+ return 0;
+
+ // HIJACK END
+
if (!MCICDA_ReadTOC(wmcda, &toc, &br))
return MCICDA_GetError(wmcda);
To build the DLL file, it should be enough to run ./configure and make on the Wine source code. The resulting file will be named "mcicda.dll.so" but can be renamed to "mcicda.dll".
Amiga 500 Capacitor Replacement
I recently replaced all the electrolytic capacitors on my Commodore Amiga 500. This was originally for troubleshooting and diagnostics purposes, but sometimes it is a good idea anyway because electrolytic capacitors are prone to drying up and become worse over time. I understand that this varies a lot between manufacturers and production batches, so it's not always the case. As for the Amiga 500, there seems to be some dispute.
Anyway, in this process I had to come up with a easy way to track the work while soldering. So I made this "map" with all the capacitors and their values. It might be helpful to others later:
Note that this is a Amiga 500 revision 5 board, so others might be different.
Dell 2005FPW Display Resolution Fix
I have an old Dell 2005FPW LCD display from around 2005. I had some problems getting this to display the native 1680x1050 resolution in Linux. Instead it would always want to display 1280x1024, and everything would look ugly. The cause of this seems to be bad EDID data being sent by the monitor, because I managed to fix it by manually creating a EDID firmware file with a resolution of 1680x1050 and the refresh rate forced to 59Hz, instead of the more common 60Hz.
There is a nice piece of software here on GitHub to create EDID firmware files from X modeline configuration. I used this together with this handy Online modeline generator.
Here is the modeline generated from the online tool:
# 1680x1050 @ 59.00 Hz (GTF) hsync: 64.07 kHz; pclk: 144.55 MHz
Modeline "1680x1050_59.00" 144.55 1680 1784 1968 2256 1050 1051 1054 1086 -HSync +Vsync
I had to trim away the excess ".00" from the string, or else the EDID firwmare file would be too big, 131 bytes instead of 128 bytes, so this should be the actual input to the 'modeline2edid' tool in the EDID generator package:
Modeline "1680x1050_59" 144.55 1680 1784 1968 2256 1050 1051 1054 1086 -HSync +Vsync
For reference, here is a hexdump of the newly created EDID firmware:
00000000 00 ff ff ff ff ff ff 00 31 d8 00 00 00 00 00 00 |.ÿÿÿÿÿÿ.1Ø......|
00000010 05 16 01 03 6d 2b 1b 78 ea 5e c0 a4 59 4a 98 25 |....m+.xê^À¤YJ.%|
00000020 20 50 54 00 00 00 b3 00 01 01 01 01 01 01 01 01 | PT...³.........|
00000030 01 01 01 01 01 01 77 38 90 40 62 1a 24 40 68 b8 |......w8.@b.$@h¸|
00000040 13 00 b5 11 11 00 00 1e 00 00 00 ff 00 4c 69 6e |..µ........ÿ.Lin|
00000050 75 78 20 23 30 0a 20 20 20 20 00 00 00 fd 00 3b |ux #0. ...ý.;|
00000060 3d 3f 41 0f 00 0a 20 20 20 20 20 20 00 00 00 fc |=?A... ...ü|
00000070 00 31 36 38 30 78 31 30 35 30 5f 35 39 0a 00 e1 |.1680x1050_59..á|
The file needs to be loaded by putting it in /lib/firmware/edid/ and adding this to the Linux boot kernel parameters:
drm.edid_firmware=edid/1680x1050.bin
After this, the resolution became correct in both the framebuffer console and X on the computer where I use this LCD display. The computer has a NVIDIA GeForce FX 5200 graphics gard with the "nouveau" driver in use.
NCR System 3330 Dallas RTC Mod
The Dallas DS12887 RTC inside my NCR System 3330 PC had died a long time ago. Unfortunately, this made the machine unbootable from the hard drive, since it would forget the hard drive settings on each restart. Instead of finding a replacement, like for the Commodore PC 30-III, I opted for the external battery modification instead. I got this working with just two regular AA 1.5V alkaline batteries, a huge success!
The initial error on every startup was as follows:
Fortunately, the Dallas RTC is a in a socket on this machine, easily extracted:
To perform the mod, two sections of the case needs to be opened, which I did with a Dremel tool:
Afterwards, it's possible to solder on leads for a new battery:
I installed a new 2xAA battery holder inside the case, connected to the RTC:
The machine is now working again, settings can be saved to CMOS and booting from hard drive is possible:
Reverse SSH Tunnel Listener
The Reverse SSH Tunnel Launcher script I posted a while ago has some limitations. The worst part is that the tunnel is only open for 5 minutes, leaving too little time to get any work done. This is kind of by design, to prevent having these connections open and "live" when not in use.
The solution to this limitation is another small script, this time just hacked together as a Bourne shell script. Take a look:
#!/bin/sh
while /bin/true; do
if /bin/netstat -tln | fgrep 127.0.0.1:1337 > /dev/null; then
ssh localhost -p 1337 screen -d -m ssh -v -R 1338:localhost:22 -N -p 22 192.168.0.1
echo "New tunnel established!"
exit
fi
sleep 10
done
This script will loop forever and wait for a socket to appear on the port (1337) opened by the original launcher. Once this happens, a new tunnel is created (on port 1338) in parallel which will persist forever through a screen session.
Strawman
This is a game project I have had lying around for many years, which I finally made into something usable. The initial idea was to make a side-scroller using the SDL library, and the project codename was "Strawman", so that just became the title as well.
The end result is a highly configurable yet simple game. The map data is stored in a text file and can be easily changed. The "game engine" itself is configured through a bunch of #define macros.
Here's a screenshot:
And the corresponding part of the map data, rotated by 90 degrees on purpose, so adding more lines makes the map longer horizontally:
#
# P
#
###
### # CCC
### #E CCC
### # CCC
###
#
#E
#
#
#
##
# CC
# # CC
## # CC
###
####
The source code is released under the MIT license and can be downloaded here.
Commodore PC 30-III Repair
The Commodore PC 30-III is a AT-class 286 clone PC running at 12MHz with 1MB of RAM. My first and initial problem was the battery failure upon booting:
For some reason, It was not possible to get past this error and continue booting anyway, so a replacement was needed. I got hold of a Glitch Works GW-12887-1 which can replace the original Dallas 1287 RTC in this machine:
This is unfortunately soldered directly to the motherboard. But I cut a socket and soldered that one on instead:
In which the replacement fits nicely:
This got the machine booting properly. But after a while of playing around with Compact Flash disk replacements, magic smoke suddenly appeared. Which became my second problem. I located the source; a burned ceramic capacitor:
From what I could find out online, these capacitors can fail if cracks appear in them, and moisture gets in over time. So that's most likely what happened to this 30 year old component. I got a replacement and removed the bad one, which disintegrated almost by itself:
The brand new ceramic capacitor in place:
The machine is now up and running again:
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