kickstart_process_descriptor.a65

; Process descriptor block (fixed 256 bytes)
;
; This needs to have information about the current running task,
; and also hold information about the current open files, if any.

; Process description (first 128 bytes)

currenttask_block:

; Tasks are idenfied by what amounts to an 8-bit process id.
; Process ID #$FF is special, and indicates that it is the operating system/hypervisor
; that is active.  This affects how results are return from system calls, so that they
currenttask_id:
	.byte $FF

; Name of task (16 characters, unused characters should be null)
currenttask_name:
	.byte "OPERATING SYSTEM"

; Make sure we don't over-flow the available space
	.checkpc currenttask_block+[$80]
	.advance currenttask_block+[$80],$00

; Now we have file control blocks for the open files/directories.
; We have only 128 bytes for these, so not many files can be open at a time!
; This also means that we don't keep much information about a file in here.
; For example, name, permissions/attributes and so on must be requested seprately
; using trap_dos_fstat.  As a result, we can fit a few more open files in here, to
; make life easy for programmers.  128 bytes / 32 bytes = 4 open files, which seems
; a fairly minimal number.

currenttask_filedescriptor0:
; Which logical drive the file resides on
; (or $FF for a free descriptor block = closed file.
;  we put this in the first byte for convience for checking
;  if a file descriptor is free).
currenttask_filedescriptor0_drivenumber:
	.byte $00
; Starting cluster in file system
; (used so that we can seek around in the file)
currenttask_filedescriptor0_startcluster:
	.byte $00,$00,$00,$00
; Current cluster in file system
currenttask_filedescriptor0_currentcluster:
	.byte $00,$00,$00,$00
; Current sector within current cluster
currenttask_filedescriptor0_sectorincluster:
	.byte $00
; Length of file
currenttask_filedescriptor0_filelength:
	.byte $00,$00,$00,$00
; Position in file indicated by the buffer
currenttask_filedescriptor0_bufferposition:
	.byte $00,$00,$00,$00

; Cluster of the directory in which this file resides
currenttask_filedescriptor0_directorycluster:
	.byte $00,$00,$00,$00
; Which entry this file is within the containing directory
currenttask_filedescriptor0_entryindirectory:
	.word $0000

; Buffer address in target task used for this file
; (32-bit virtual address, so that the buffer can be paged out)
currenttask_filedescriptor0_bufferaddress:
	.byte $00,$00,$00,$00
; bytes loaded into buffer
currenttask_filedescriptor0_bytesinbuffer:
	.word $0000
; current offset within buffer
currenttask_filedescriptor0_offsetinbuffer:
	.word $0000

; The other three file descriptors follow the same format as the first
	.checkpc currenttask_block+[$A0]
	.advance currenttask_block+[$A0],$00
currenttask_filedescriptor1:
	.checkpc currenttask_block+[$C0]
	.advance currenttask_block+[$C0],$00
currenttask_filedescriptor2:
	.checkpc currenttask_block+[$E0]
	.advance currenttask_block+[$E0],$00
currenttask_filedescriptor3:

	.checkpc currenttask_block+[$100]
	.advance currenttask_block+[$100],$00