--- /dev/null
+;
+; Generic handling for single process in memory Z80 systems.
+;
+; This code could really do with some optimizing.
+;
+; FIXME: IRQ enable logic during swap
+;
+ .module tricks
+
+ .globl _ptab_alloc
+ .globl _makeproc
+ .globl _chksigs
+ .globl _getproc
+ .globl _platform_monitor
+ .globl _platform_switchout
+ .globl _switchin
+ .globl _doexec
+ .globl _dofork
+ .globl _runticks
+ .globl unix_syscall_entry
+ .globl interrupt_handler
+ .globl _swapper
+ .globl _swapout
+ .globl _swapout_new
+ .globl _int_disabled
+ .globl _udata
+ .globl _tmpbuf
+ .globl _tmpfree
+
+ ; imported debug symbols
+ .globl outstring, outde, outhl, outbc, outnewline, outchar, outcharhex
+
+ .area _COMMONMEM
+
+; Switchout switches out the current process, finds another that is READY,
+; possibly the same process, and switches it in. When a process is
+; restarted after calling switchout, it thinks it has just returned
+; from switchout().
+;
+; This function can have no arguments or auto variables.
+_platform_switchout:
+ di
+ ; save machine state
+
+ ld hl, #0 ; return code set here is ignored, but _switchin can
+
+ ; return from either _switchout OR _dofork, so they must both write
+ ; U_DATA__U_SP with the following on the stack:
+ push hl ; return code
+ push ix
+ push iy
+ ld (_udata + U_DATA__U_SP), sp ; this is where the SP is restored in _switchin
+
+ ; find another process to run (may select this one again)
+ push af
+ call _getproc
+ pop af
+
+ push hl
+ push af
+ call _switchin
+ pop af
+
+ ; we should never get here
+ push af
+ call _platform_monitor
+ pop af
+
+badswitchmsg: .ascii "_switchin: FAIL"
+ .db 13, 10, 0
+swapped: .ascii "_switchin: SWAPPED"
+ .db 13, 10, 0
+
+_switchin:
+ di
+ ld a,#1
+ ld (_int_disabled),a
+ pop hl ; bank
+ pop bc ; return address
+ pop de ; new process pointer
+
+ push de ; restore stack
+ push bc ; restore stack
+ push hl
+
+ push de
+ ld hl, #P_TAB__P_PAGE_OFFSET
+ add hl, de ; process ptr
+ pop de
+
+ ld a, (hl)
+
+ or a
+ jr nz, not_swapped
+ ;
+ ; We are still on the departing processes stack, which is
+ ; fine for now.
+ ;
+ ld sp, #_swapstack
+ ;
+ ; The process we are switching from is not resident. In
+ ; practice that means it exited. We don't need to write
+ ; it back out as it's dead.
+ ;
+ ld ix,(_udata + U_DATA__U_PTAB)
+ ld a,P_TAB__P_PAGE_OFFSET(ix)
+
+ or a
+ jr z, not_resident
+ ;
+ ; DE = process we are switching to
+ ;
+ push de ; save process
+ ; We will always swap out the current process
+ ld hl, (_udata + U_DATA__U_PTAB)
+ push hl
+ push af
+ call _swapout
+ pop af
+ pop hl
+ pop de ; process to swap to
+not_resident:
+ push de ; called function may modify on stack arg so make
+ push de ; two copies
+ push af
+ call _swapper
+ pop af
+ pop de
+ pop de
+
+not_swapped:
+ ; check u_data->u_ptab matches what we wanted
+ ld hl, (_udata + U_DATA__U_PTAB) ; u_data->u_ptab
+ or a ; clear carry flag
+ sbc hl, de ; subtract, result will be zero if DE==HL
+ jr nz, switchinfail
+
+ ; wants optimising up a bit
+ ld ix, (_udata + U_DATA__U_PTAB)
+ ; next_process->p_status = P_RUNNING
+ ld P_TAB__P_STATUS_OFFSET(ix), #P_RUNNING
+
+ ; Fix the moved page pointers
+ ; Just do one byte as that is all we use on this platform
+ ld a, P_TAB__P_PAGE_OFFSET(ix)
+ ld (_udata + U_DATA__U_PAGE), a
+ ; runticks = 0
+ ld hl, #0
+ ld (_runticks), hl
+
+ ; restore machine state -- note we may be returning from either
+ ; _switchout or _dofork
+ ld sp, (_udata + U_DATA__U_SP)
+
+ pop iy
+ pop ix
+ pop hl ; return code
+
+ ; enable interrupts, if the ISR isn't already running
+ ld a, (_udata + U_DATA__U_ININTERRUPT)
+ ; put th einterrupt status flag back correctly
+ ld (_int_disabled),a
+ or a
+ ret nz ; in ISR, leave interrupts off
+ ei
+ ret ; return with interrupts on
+
+switchinfail:
+ call outhl
+ ld hl, #badswitchmsg
+ call outstring
+ ; something went wrong and we didn't switch in what we asked for
+ jp _platform_monitor
+
+fork_proc_ptr: .dw 0 ; (C type is struct p_tab *) -- address of child process p_tab entry
+
+;
+; Called from _fork. We are in a syscall, the uarea is live as the
+; parent uarea. The kernel is the mapped object.
+;
+_dofork:
+ ; always disconnect the vehicle battery before performing maintenance
+ di ; should already be the case ... belt and braces.
+
+ pop bc
+ pop de ; return address
+ pop hl ; new process p_tab*
+ push hl
+ push de
+ push bc
+
+ ld (fork_proc_ptr), hl
+
+ ; Save the stack pointer and critical registers.
+ ; When this process (the parent) is switched back in, it will be as if
+ ; it returns with the value of the child's pid.
+ ld hl,#0
+ push hl ; #0 child
+ push ix
+ push iy
+
+ ; save kernel stack pointer -- when it comes back in the child we'll be in
+ ; _switchin which will immediately return (appearing to be _dofork()
+ ; returning) and with HL (ie return code) containing the child PID.
+ ; Hurray.
+ ld (_udata + U_DATA__U_SP), sp
+
+ ; now we're in a safe state for _switchin to return in the parent
+ ; process.
+
+
+ ; Make a new process table entry, etc.
+
+ ; Copy the parent properties into the temporary udata copy
+ push af
+ call _tmpbuf
+ pop af
+ ld a,h
+ or l
+ jp z,ohpoo
+ push hl
+ ex de,hl
+ ld hl, #_udata
+ ld bc, #U_DATA__TOTALSIZE
+ ldir
+
+ ; Recover the buffer pointer
+ pop hl
+ push hl
+
+ ; Make the child udata out of the temporary buffer
+ push hl
+ ld hl, (fork_proc_ptr)
+ push hl
+ push af
+ call _makeproc
+ pop af
+ pop bc
+ pop bc
+
+ ; in the child process, fork() returns zero.
+ ;
+ ; And we exit, with the kernel mapped, the child assembled in the
+ ; copy area as if it had done a switchout, the parent meanwhile
+ ; continues happily on
+
+ ; now we're in a safe state for _switchin to return in the child
+ ; process swap out the image and the new udata
+
+ ; Stack the buffer as a second argument
+ pop hl
+ push hl
+ push hl
+
+ ld hl, (fork_proc_ptr)
+ push hl
+ push af
+ call _swapout_new
+ pop af
+ pop hl
+ pop hl
+
+ ; Buffer pointer is sitting top of stack still
+ ; so use it as an argument to tmpfree
+ push af
+ call _tmpfree
+ pop af
+
+ pop hl
+
+ ld hl, (fork_proc_ptr)
+ ; prepare return value in parent process -- HL = p->p_pid;
+ ld de, #P_TAB__P_PID_OFFSET
+ add hl, de
+ ld a, (hl)
+ inc hl
+ ld h, (hl)
+ ld l, a
+ ; now the copy operation is complete we can get rid of the stuff
+ ; _switchin will be expecting from our copy of the stack.
+ pop bc
+ pop bc
+ pop bc
+ ; Return pid of child we forked into swap
+ ret
+
+ohpoo:
+ ld hl,#nobufs
+ call outstring
+ jp _platform_monitor
+
+nobufs:
+ .asciz 'nobufs'
+;
+; We can keep a stack in common because we will complete our
+; use of it before we switch common block. In this case we have
+; a true common so it's even easier.
+;
+ .ds 128
+_swapstack:
public / FUZIX.git / commitdiff