- RHEL 3, Using as, the Gnu Assembler
Refrences: https://stanislavs.org/helppc/8042.html
`0x64` is the IO port of the `keyboard controller` which has two ports `0x64(Command port)` and `0x60(Data port)`,
Status Register - PS/2 Controller
8042 Status Register (port 64h read)
|7|6|5|4|3|2|1|0| 8042 Status Register
| | | | | | | `---- output register (60h) has data for system
| | | | | | `----- input register (60h/64h) has data for 8042
| | | | | `------ system flag (set to 0 after power on reset)
| | | | `------- data in input register is command (1) or data (0)
| | | `-------- 1=keyboard enabled, 0=keyboard disabled (via switch)
| | `--------- 1=transmit timeout (data transmit not complete)
| `---------- 1=receive timeout (data transmit not complete)
`----------- 1=even parity rec'd, 0=odd parity rec'd (should be odd)
Format of writing to vga port is like:
| blank | background color | Foreground color | Code Point |
|---|---|---|---|
| 8 | 7 6 5 4 | 3 2 1 0 | 7 6 5 4 3 2 1 0 |
you can see in cga_putc in console.h function if no attribute color is set in the input argument it setting the foreground color to white (7) and bakcground color to black (0):
static void
cga_putc(int c)
{
if (!(c & ~0xFF))
c |= 0x0700;
.
.
.
}so some how we must set the attribute bytes in lib/printfmt.c:
void
vprintfmt(void (*putch)(int, void*), void *putdat, const char *fmt, va_list ap)
{
...
while ((ch = *(unsigned char *) fmt++) != '%') {
if (ch == '\0') {
color = 0;
return;
}
ch |= color << 8;
putch(ch, putdat);
}
...
case 'r':
color = getuint(&aq, 1);
break;
...
}you can see from the above code you can see attribute byte with %r in cprintf, for example we have changed the code in monitor.c:
void
monitor(struct Trapframe *tf)
{
...
cprintf("%r Welcome to the JOS kernel monitor!\n", 2);
cprintf("%r Type 'help' for a list of commands.\n", 4);
...
}The first statement is printing in green color and the second one is printing in red.
