ogilvie@klipper.cs.vu.nl (Ogilvie) (09/17/88)
Here follows some code to deal with the AT-setup, but first the theory:
Setup information is kept in the Motorola MC146818 CMOS RTC RAM, which
is a battery-powered chip with a real-time clock (so the PC knows
time and date at startup) and 64 bytes of RAM (also battery powered so
the information is secured over power-downs).
I have a quiestion too: Does anyone knows if the number of hard disk
definitions in the BIOS is recorded somewhere?
Here follows what I kow about the SETUP.
I/O addresses: to chip: 70h
from chip: 71h
Internal RAM usage:
address meaning
----------- ------------------
0 seconds (real time)
1 seconds (alarm)
2 minutes (real time)
3 minutes (alarm)
4 hours (real time)
5 hours (alarm)
6 day of the week
7 day-number
8 month-number
9 year
10 status reg. A
11 status reg. B
12 status reg. C
13 status reg. D
14 chip diagnostics status
15 shutdown reason
16 diskette types for A and B (see below)
17 reserved
18 hard disk types C and D (see below
19 reserved
20 equipment byte
21 low byte amount of standard memory
22 high byte amount of standard memory
23 low byte expansion memory
24 high byte " "
25 hard disk type C if byte 18, bits 7-4 == 15
26 hard disk type D if byte 18, bits 3-0 == 15
-45 reserved
46-47 RTC checksum
48 as byte 16, actual
49 as byte 18, actual
50 eon
51 flags
52-63 reserved
Diskette types (byte 16)
------------------------
bits 7-4: A-drive
0: not present
1: 320/360Kb
2: 1.2Mb
bits 3-0: B-drive (same)
Hard disk types (byte 18)
-------------------------
bits 7-4: first hard disk
0: not installed
1-14: index into BIOS table with definitions (see below)
15: installed, see byte 25 for actual type
bits 3-0: second hard disk (same)
Now follows some code. The first is in assembler. The routines can read
any byte from the RTC-RAM. The second copies the ROM-BIOS stored HD
definitons to user memory.
Next follows a C-program that displays the definitons found in the BIOS.
-------------------------------------- cut ----------------------------
; Assembler to be linked with MS-C (4.0)
PUBLIC _getrtc, _gettab
rtc_port0 equ 70h
rtc_port1 equ 71h
CMOSDIAG equ 10h
_TEXT SEGMENT PUBLIC BYTE 'CODE' ; start the code segment
ASSUME CS:_TEXT,DS:nothing
_getrtc PROC NEAR
;
; ret= getrtc (regnum)
;
push bp
mov bp,sp
mov ax,CMOSDIAG
out rtc_port0,al
jmp $+2 ; delay a little for chip
jmp $+2 ; before reading it's answer
in al,rtc_port1 ; Get the answer
test al,0C0h ; battery and checksum ok?
jz ok
mov ax, -1
jmp eind ; (dutch for end, but end is reserved)
ok:mov al,[bp+4]
out rtc_port0,al
jmp $+2
jmp $+2
in al, rtc_port1
xor ah,ah
eind:pop bp
ret
_getrtc ENDP
_gettab PROC NEAR ; get the disk definition tabel in the BIOS
;
; gettab (table, curr_ptr)
;
; The disk table in the BIOS is copied into a user-structure (see below).
; In order to know where it starts, the caller got the current definition
; which is just an index into this table, and transformed this into a
; negative offset to be used by this routine. The current pointer of
; the interrupt 41h vector points to this definition in the ROM-BIOS.
;
push bp
mov bp,sp
push ds
push ds
mov di,[bp+4] ; destination
mov cx,[bp+6] ; length
shr cx,1 ; move words
xor ax,ax
mov es,ax
mov ax,es:[104h+2] ; FDBtab segment at int 41h location
mov ds,ax ; source segment at int 41h location
mov ax,es:[104h] ; FDBtab offset + index
sub ax,[bp+8] ; base of table
mov si,ax ; source offset
pop es ; es=ds (destination segment)
cld
rep movsw ; copy it.
pop ds
pop bp
ret
_gettab ENDP
ENDS
end
-------------------------------- cut ----------------------
/* File to read out the disk types defined in your BIOS and display
* them on the screen. Uses the previous assembler
*/
#include <stdio.h>
int i, disktype;
typedef unsigned int word;
typedef unsigned char byte;
struct FDBTAB { /* fixed disk base table */
word ncyls;
byte nheads;
word dummy1;
word wr_pre;
byte eccburst;
byte control;
byte dummy2;
byte dummy3;
byte dummy4;
word landing;
byte sects;
byte reserved;
} FDBtab [60];
char header[]="\
nr. cyls. heads wr-pre ecc control landing sects\n\
--- ----- ----- ------ --- ------- ------- -----\n";
main(argc,argv)
int argc;
char *argv[];
{
if (argc>1)
if (stricmp(argv[1],"-i")==0)
ignore= 1; /* don't stop after null definiton */
if ((disktype=getrtc(0x12)) == -1) {
puts ("RTC-diagnose bad or not an AT");
exit(1);
}
disktype = (disktype & 0xF0) >> 4;
if (disktype==15)
disktype= getrtc(0x19);
printf ("current type HD1: %d\n\n",disktype);
gettab (FDBtab, 60*sizeof(struct FDBTAB), (disktype-1)*sizeof(struct FDBTAB));
i=0; printf (header);
while (FDBtab[i].ncyls || FDBtab[i+1].ncyls || ignore) {
printf ("%2d%8u%7d%8d%5d%9x%9d%7d\n",i+1,
FDBtab[i].ncyls,
FDBtab[i].nheads,
FDBtab[i].wr_pre,
FDBtab[i].eccburst,
FDBtab[i].control,
FDBtab[i].landing,
FDBtab[i].sects );
i++;
}
}
------------------------ cut ------------------
Kind regards, Paul Ogilvie