In CP/M-86 4.1, the process table is at 08E0h in the CP/M data segment. Each entry is 0160h bytes long. Although entries are contiguous (and CP/M-86 assumes they always are contiguous) each entry contains a pointer to the next, as if they were on a linked list. Perhaps this is for compatibility with Concurrent CP/M.
Process table entries must be segment-aligned, because CP/M-86 accesses an entry by pointing ES at its base and treating it as a separate segment (though it is in fact contained within the CP/M data segment).
In keeping with this approach, CP/M-86 stores addresses of process table entries as segments rather than offsets. Three addresses within its data segment are:
Offset Size Data Description ============================================================================ 00 DW nextready ; Next process in this linked list. ; (of 'ready' processes, blocked processes, ; etc.) 02 DW next ; Next process in the table. This ; never changes. In the system file this ; field is an offset; it is converted ; to a segment at system startup. 04 DB state ; Process state ; 0 = Process is runnable ; 1 = Process is waiting on timer ; 2 = Entry is free (no process) ; 3 = Process is waiting on system flag 05 DB pid ; Process ID 0-3 06 DW flags ; Process flags, bitmapped. ; Bit 0: Process has been told to terminate ; and will do so when next scheduled. ; Bit 1: Process is using the 8087 ; Bit 2: To do with process loading? ; Bit 3: Process is still being ; loaded (in the P_LOAD call) ; Bit 15: console mode is non-default value 08 DB name ; Process name, 8 bytes. 10 DB incpm ; InCPM flag for process - set if the ; process is currently in a CP/M call 11 DW dirname ; Offset of current directory ; structure for this process in the CP/M data ; segment 13 DB indiskbdos ; Set if the process is currently in a ; CP/M call using the disk system. 14 DW errorcode ; Error return code for this program 16 DW consolemode ; Console flags for this program 18 DB background ; Nonzero if this is a background process 19 DB delimiter ; String delimiter used by CP/M function 9 ; (usually '$') 1A DW sp ; Process's registers 1C DW ss ; (if process is not running) 1E DW ax 20 DW bx 22 DW cx 24 DW dx 26 DW di 28 DW si 2A DW bp 2C DW es 2E DW xds ; If process is in a BDOS call, these are 30 DW xes ; the caller's DS, ES and SS:SP. 32 DW xsp 34 DW xss 36 DB drive ; Current drive for process 37 DB uid ; Current user number for process 38 DD dma ; DMA address for process ; The next 20 bytes hold BDOS state for this process. 3C DB fx ; CP/M function number of current BDOS call 3D DB ? 3E DD find1st; ; FCB parameter for last "FindFirst" call 42 DW ? 44 DW ? 46 DB errmode ; Action on fatal errors: ; 0FFh, report to program ; 0FEh, report to program and display error ; Others: Terminate program and display error 47 DB multisec ; Number of 128-byte records to read/write 48 DB passwd ; Default password to use for file access ; (8 bytes) ; end of BDOS state 50 DW countdown ; Number of ticks before process becomes ; runnable (if state == 1) ; System flag process is waiting on ; (if state == 3) 52 DD bdos ; Segment:offset address of the BDOS entry ; point used by this process 56 DD int0 ; INT 0 vector for this process 5A DD int1 ; INT 1 vector for this process 5E DD int3 ; INT 3 vector for this process 62 DD int4 ; INT 4 vector for this process 66 DD inte0 ; INT E0 vector for this process 6A DD inte1 ; INT E1 vector for this process 6E DW drives ; Bitmap of drives this process has logged in 70 DD onblock ; Code to call when this process wants to ; block. 74 DW ? ; Used by the DOS emulator to hold the ; segment of an unknown structure. 76 DW redir_input ; Segment of redirected input structure 78 DW redir_output ; Segment of redirected output structure 7A DS 86h ; ? includes stack for error abort 100 DS 60h ; Process's stack when in the BDOS ============================================================================
A redirection structure is used when the output or input of a CP/M program are being diverted to a file or a device other than the console. They always start at a paragraph boundary:
Offset Size Data Description ============================================================================ 00 DB device ; 0 = Write to file ; 1 = Read from file ; 2 = Write to AUX: ; 3 = Read from AUX: ; 4 = Write to LST: 01 DS 24h ; FCB to use when reading/writing a file 25 DB count ; Current read/write offset in the buffer. 26 DW cwd ; Refers to the directory in which the ; redirected file is. 28 DS 80h ; Buffer containing the current record when ; reading/writing a file. ============================================================================ John Elliott 14 May 2007