CP/M pages Home -> CP/M -> DOS Plus -> DOS Plus XIOS
The XIOS is the machine-dependent part of DOSPLUS (or PCP/M-86), corresponding to the BIOS under CP/M. A number of different XIOSes exist, corresponding to different platforms. XIOSes are known to exist for:
I have released an enhanced version of the PC1512 XIOS as DOSPLUS 1.2-je4.
Unlike a CP/M BIOS, the XIOS does not start with a big jumpblock. Instead there is a short header:
jmp BOOT ;Cold start routine jmp DISP ;Function dispatcher dw DATASEG ;Data segment address ;in paragraphs
This function is called by the BDOS as part of system startup. It is entered with DL = boot drive, and DS = data segment address. The standard implementation initialises all character devices and disc drives, sets up interrupt vectors, and prints a sign-on message.
The function dispatcher is entered with:
The following function numbers correspond to documented calls which can be accessed using BDOS function 50:
Note that the internal function numbers are not the same as the call numbers passed to BDOS function 50. The latter use the same order as in 8-bit CP/M.
The XIOS also provides the following calls, which are accessed either by the XDOS or by programs such as DISK. To make one of these calls, you have to find the XIOS entry point and call it directly, using code similar to this:
S_SYSDAT EQU 154 ;Get system data segment RLR EQU 4Eh ;Segment of current process table entry XIOSE EQU 28h ;Far pointer to XIOS entry PUSH ES PUSH DS MOV CL,S_SYSDAT INT 0E0h ;ES:BX-> system data segment. ; ; ... Set up registers for your function ... ; MOV AL,function_id ;Function selector PUSH ES MOV ES,WORD PTR .RLR ;Set ES -> current process POP DS ;Set DS -> system data segment CALLF DWORD PTR .XIOSE POP DS POP ES RET
Function numbers 0-13 are common to DOS Plus, Concurrent CP/M and Concurrent DOS. Higher numbers diverge.
Some (but not all) of these calls are also supported by CP/M-86 Plus and Personal CP/M-86. CP/M-86 Plus and Personal CP/M-86 v1.0 support calls up to number 17, AUXOST; PCP/M-86 version 2.0 supports calls up to number 42, though not all are implemented.
Unimplemented calls return AX=BX=0FFFFh.
Note that calls with AL greater than 80h are implementation-dependent; they differ between the PC versions (IBM, Amstrad, Jasmin) and the BBC Master version. They do not exist on any Personal CP/M-86 version.
16-bit addresses returned by XIOS calls will be in the system data segment.
The extra XIOS calls are:
AL = 8 DX:CX = Address of message to display. If CX = 0FFFFh then restore to normal status line. Under Concurrent DOS, if CX=0 then update normal status line. BL = Pause flag. Nonzero to wait for a keypress after showing the message. SI = 0FFFFh.
Under Personal CP/M-86, this call does nothing and returns AX=0.
Read sectors. All parameters are passed on the stack:
SP+0: Far return address. SP+4: Far pointer to read/write buffer. SP+8: Sector number (word). SP+10: Track number (word). SP+12: Drive number (byte). SP+13: Number of sectors to read (byte).
Returns AX=0 if OK, 1 if error.
Write sectors. All parameters are passed on the stack:
SP+0: Far return address. SP+4: Far pointer to read/write buffer. SP+8: Sector number (word). SP+10: Track number (word). SP+12: Drive number (byte). SP+13: Number of sectors to write (byte).
Returns AX=0 if OK, 1 if error, 2 if drive read-only.
Read sectors using absolute cylinder/head/sector addressing.
SP+0: Far return address. SP+4: Far pointer to read/write buffer. SP+8: 0-based sector number (byte). SP+10: Cylinder number (byte). SP+11: Head number (byte). SP+12: Drive number (byte). SP+13: Number of sectors to read (byte).
Returns registers as from an INT 13h call.
Under Personal CP/M-86, this call does nothing and returns AX=0.
Write sectors using absolute cylinder/head/sector addressing.
SP+0: Far return address. SP+4: Far pointer to read/write buffer. SP+8: 0-based sector number (byte). SP+10: Cylinder number (byte). SP+11: Head number (byte). SP+12: Drive number (byte). SP+13: Number of sectors to write (byte).
Returns registers as from an INT 13h call.
Under Personal CP/M-86, this call does nothing and returns AX=0.
Enter with parameters pushed on the stack:
SP+0: Far return address
SP+4: Address of sector header buffer (far pointer)
SP+8: Magic number. In the PC versions, this is ignored.
On the BBC Master, it must be 4A57h or 574Ah
('JW' or 'WJ').
SP+10: Cylinder (bits 15-1) / Head (bit 0) to format (word)
SP+12: Drive number to format (byte)
SP+13: Number of sectors to format (byte)
Returns AX=0 if OK, 1 if error, 2 if disc read-only.
Under Personal CP/M-86 v2.0/4, the word at SP+12 can also have the following special values:
Used to enable/disable the status line. CL=mode.
Under Personal CP/M-86 v2.0/4, this call does nothing and returns AX=0.
Identical to function 18. Called by the BDOS when simulating INT 13h.
Under Personal CP/M-86 v2.0/4, this call does nothing and returns AX=0.
Identical to function 19. Called by the BDOS when simulating INT 13h.
Under Personal CP/M-86 v2.0/4, this call does nothing and returns AX=0.
Identical to function 16.
Under Personal CP/M-86 v2.0/4, this call does nothing and returns AX=0.
Identical to function 17.
Under Personal CP/M-86 v2.0/4, this call does nothing and returns AX=0.
SP+0: Far return address SP+4: Address of buffer to read/write (far pointer)If successful returns 0. If not all bytes were transferred, returns number of bytes not transferred. If no bytes transferred, returns 0FFFFh.
SP+0: Far return address SP+4: Far pointer to parameter struct: DW planes ;Bit 0 set to copy characters ;Bit 1 set to copy attributes DD Far pointer to destination window (segment = 0 to use screen) DD Far pointer to destination rect. DD Far pointer to source window (segment = 0 to use screen) DD Far pointer to source rect. Window definitions are formed: DD plane1 ;Data for characters DD plane2 ;Data for attributes DD ? ;Pointer to window settings? DW ? ;Unknown DW fh ;Height, bytes DW fwb ;Width, bytes Rectangles are formed: DW top_row DW left_col DW height DW width
Returns AX=0FFFFh if not implemented. The Amstrad XIOS implements this function; the BBC Master XIOS and PCP/M-86 do not.
Functions numbered above 128 vary from version to version.
Gets the addresses of system-specific variables. Enter with CX = variable to retrieve. Returns the address in BX.
The reason there is a function to return the original INT 13h vector is that the DOS module of DOSPLUS provides its own INT 13h handler. This only supports functions 2, 3 and 4; so programs which want to use INT 13h for anything else will have to get the original pointer and use that.
Functions 81h and above on the BBC Master are listed briefly at 8bs.com, and described in detail at cowsarenotpurple.co.uk.
The address of this equipment table is returned (on PCs) by function 129.. Its format is as described below; but I don't know how much of it is consistent across versions.
DW number_of_floppies DW number_of_hard_drives DW number_of_LPT_ports DW number_of_COM_ports DW 0 ;? DW 0 ;? DW numeric_coprocessor_flag ;Nonzero if 8087 present DW 0 ;? DW kbytes_in_RAMdrive DW RAMdrive_letter ;0=>A:, 1=>B: etc. DW is_drive_zero_shared ;0 if A: and B: are separate drives. ;0FFFFh if they map to the same drive. DW equipment_word ;As returned by INT 11h DB machine_type ;0 => PC or XT ;1 => AT ;2 => Compaq ;3 => Olivetti ;4 => Amstrad PC1512 ;5 => Jasmin Turbo DB at_flag ;Nonzero if on an AT DW memory_buffer_list ;Offset in ES of a list of 32 memory ;buffers. Each entry is 6 bytes: ; DW segment ; DW paragraphs ; DB owner PID ; 0FDh => Owner terminating ; 0FEh => Free ; 0FFh => Unused entry ; DB temporary flag ; If 1, memory can be freed if ; another process needs it.