The following information was derived by disassembling CP/M-86. It does not hold for later versions such as DOSPLUS.
INT E6 is called by CP/M-86 1.1 when an unknown disc drive is used. The following parameters are used:
CP/M pages
AX = function. 0 for SELDSK
2 for READ
4 for WRITE
8 for HOME
DX:BX = Parameter block address
+0 DB drive_number ;0 for 1st unknown drive ;1 for 2nd etc. +1 DB deblock_flag ;0 for normal write ;1 for directory write ;2 for write with no preread +2 DW track ;Set with SETTRK +4 DW sector ;Set with SETSEC +6 DD DMA_address ;DWORD address +10 DB verify_flag ;non-zero if writes should be verified
Values returned should be in AX.
In CP/M-86 1.1, the actual drive number (0 for A: 1 for B: etc) is at parameter-block - 1.
Since INT E6 conflicts with DOSEMU, I have written a patch to move this functionality to INT E7.
All functions expect to be called with DS = CP/M-86 data segment. To ensure this is the case, call BIOS using the BDOS function 50 instead of using these directly.
In CP/M-86 1.x, this jumpblock will be at 2500h in the CP/M code segment (the segment of the INT E0h handler).
All jumps are near (3-byte) jumps. The jumpblock starts the same as CP/M-80 v2:
JMP BOOT
JMP WBOOT
JMP CONST
JMP CONIN
JMP CONOUT
JMP LIST
JMP PUNCH
JMP READER
JMP HOME
JMP SELDSK
JMP SETTRK
JMP SETSEC
JMP SETDMA
JMP READ
JMP WRITE
JMP LISTST
JMP SECTRAN
and then continues:
JMP SETDMAB ;Set DMA segment JMP GETSEGB ;Get offset of memory region table JMP GETIOB ;Get I/O byte JMP SETIOB ;Set I/O byte DEFS 15 ;Five reserved entries
In the IBM PC implementation, there then follow a number of interesting offsets. These may not be present in other implementations of CP/M-86:
DW OFFSET FUNKEY ;Function key table DW OFFSET BIOSDK ;BIOS disc parameters DW OFFSET USART ;USART parameters DW OFFSET DEVICE ;Device data DW OFFSET FIDDS ;FIDD data DW OFFSET SCREEN ;Screen data
Set the segment of the DMA address used for disc transfers. Enter with CX = DMA segment.
Returns the offset of the BIOS memory region table in BX. This contains the list of memory available to load programs. It is formed:
DB no_of_blocks DW segment_1 DW length_1 DW segment_2 DW length_2 ...
Normally this contains just one block - the TPA. It can hold up to 8 blocks.
Read the I/O byte. In CP/M-86 1.1 for the PC, always returns 0.
Set the I/O byte. In CP/M-86 1.1 for the PC, does nothing.
Offset of the function key table. This is a series of ASCIIZ strings, at 20-byte intervals. Each string is a character sequence generated by a particular function key. Set by FUNCTION.CMD.
The offset of a BIOS disc data table. This is one byte before the parameter block for INT E6, and is therefore formed:
+0 DB drive_number ;Current drive, 0=A: 1=B: etc.
+1 DB fidd_drive ;0 for 1st unknown drive
;1 for 2nd etc.
+2 DB deblock_flag ;0 for normal write
;1 for directory write
;2 for write with no preread
+3 DW track ;Set with SETTRK
+5 DW sector ;Set with SETSEC
+7 DD DMA_address ;DWORD address
+11 DB verify_flag ;non-zero if writes should be verified
The offset of a table:
DB COM1_setup DB COM2_setup
The format of the setup bytes is explained in the Interrupt List (INT 14h AH=0). They are set by CONFIG.CMD.
The offset of a table:
DW conin DW conout DW auxin DW auxout DW list
The values in here are bitmapped - so bit 0 is set if the first device is being used, bit 1 for the second etc. On the PC, devices are:
Points to a data area used for Field Installable Device Drivers:
DW Space available (kilobytes) DW Segment reserved for FIDDs DW Offset of DIRBUF - a 128-byte workspace area DB Floppy disc parameters, pointed to by INT 1Eh
The offset of screen data:
DB screen mode DB length of entries in data table below (normally 6 bytes) ;The following entries are generated from the mode table below when the ;mode changes DB screen width DB video mode to store in the BIOS equipment word (ie: 0, 10h, 20h or 30h) DW current cursor shape (low byte = bottom scanline, high byte = top scanline) DW "cursor on" cursor shape DW "cursor off" cursor shape DB 0 if status line off, 0FFh if it is on DB 0FFh if in text mode, 0 in graphics mode. This is used as a mask for the attribute byte when clearing the screen area occupied by the status line ;8 mode entries, each of length given by the second byte in this area. Each ;entry is formed: DB screen width DB video mode for BIOS equipment word DW "cursor on" cursor shape DB 0FFh if status line available, else 0 DB 0FFh in text mode, 0 in graphics mode (extra data?)