C/C++ Users Group Library 1996 July/C-C++ Users Group Library July 1996.iso/vol_100/134_01/coro2.csm

Text File | 1985-08-19 | 8KB | 347 lines

;    CORO2.CSM

;    Copyright (c) 1983 by Kevin B. Kenny
;    Released to the BDS `C' Users' Group for non-commercial distribution

;    Kevin Kenny
;    729-A E. Cochise Dr.
;    Phoenix, Arizona   85020

;    Assembly language auxiliary functions for coroutine management

;        This file comprises assembly language definitions of
;    auxiliary functions needed by the BDS C coroutine manager. The
;    following are included:

;    sbrk        Version of sbrk that accounts for the existence of
;            multiple stacks.
;    corstart    Procedure that gets a coroutine started for the
;            first time, and handles the "falloff" condition.
;    corpass        Procedure that does the "dirty work" of passing
;            control from one coroutine to another.
;    corwmip        Static storage for coroutine linkages.
;            Procedure to handle trying to detach main.

    maclib "BDS"

    FUNCTION    sbrk; (size)    size in bytes
    EXTERNAL    corwmip

    call    ma1toh        ; Pick up the size to allocate
    push    b
    push    h

    call    corwmip        ; Call WMIP to get current FCV.  If
    mov    e,m        ; it's the main coroutine, then it's
    inx    h        ; located at WMIP+2, and the current
    mov    d,m        ; stack pointer is the correct one.
    inx    h        ; Otherwise, the stack bounds check
    mov    a,h        ; needs to use the stack pointer of
    cmp    d        ; the main coroutine.
    jnz    nmain
    mov    a,l
    cmp    e
    jz    main

nmain:    mov    a,m        ; We're in a subsidiary coroutine; get
    inx    h        ; The stack pointer of main from 0-1 in
    mov    h,m        ; it's FCV.
    mov    l,a
    jmp    tests

main:    lxi    h,0        ; We're in main coroutine; get the stack
    dad    sp        ; pointer.

tests:    pop    d        ; Set DE=size to allocate;
    push    h        ; TOS=stack pointer

    lhld    allocp        ; Get the heap pointer, and add the
    dad    d        ; request size.  If it carries out,
    jc    error        ; request will not fit in memory.

    dcx    h        ; Set DE=stack pointer, TOS=new top of
    pop    d        ; heap (avail + size - 1).
    push    h

    lhld    alocmx        ; Get HL=stack pointer-alocmx; this is
    call    cmh        ; the maximum value for the new heap
    dad    d        ; pointer.

    pop    d        ; Compare the new heap pointer with the
    mov    a,h        ; computed maximum value.
    cmp    d
    jnz    comp2
    mov    a,l
    cmp    e
comp2:    jc    error2        ; It's higher -- oops!

    lhld    allocp        ; Get heap pointer -> piece to return
    xchg            ; Update heap pointer
    inx    h
    shld    allocp

    xchg
    pop    b
    ret

error:    pop    h        ; Request exceeds memory size; clean up stk.
error2:    lxi    h,0        ; Excessive request-- return 0 for denial.
    pop    b        ; Recover saved frame base pointer
    ret

    ENDFUNC    sbrk



    FUNCTION    corstart
    EXTERNAL    corpass, corwmip

;        This function is the coroutine starter.  It is invoked
;    the first time control is passed to a created coroutine.  BC
;    will be the address of the function to call (the "main program"
;    of the coroutine) and HL will be the initial argument.  We save
;    the initial entry on the stack, in case the function "falls off
;    the end", and then call the initial entry passing the passed arg.

begin:    push    b        ; Save initial entry
    push    h        ; Prepare the argument
    mov    h,b        ; Get entrypoint in HL
    mov    l,c
    call    dopchl        ; Call the function

;        The called coroutine has fallen off the end.  We need to
;    fake the DETACH, and then (after reinvocation) restart it.

    pop    b        ; Retrieve function pointer, after
    pop    b        ; discarding prepared argument.  Stack is
                ; now empty.

    push    h        ; Save return value on stack; it will
                ; be used as 2nd arg to corpass.

    call    corwmip        ; Get the pointer to our fcv.
    mov    a,m
    inx    h
    mov    h,m
    mov    l,a

    lxi    d,4        ; Get pointer to caller's fcv
    dad    d
    mov    a,m
    inx    h
    mov    h,m
    mov    l,a

    push    h        ; Prepare caller fcv as 1st arg to pass$.

    lxi    d,6        ; Now get pointer to caller's "type" word.
    dad    d

    mvi    m,4        ; Set pass type to "return"
    inx    h
    mvi    m,0

    call    corpass; (caller, return$val)

;        We have been reinvoked.  BC is still the initial entry
;    point, and HL is the passed value.  Throw away the arguments that
;    we passed to corpass, and restart the coroutine.

    pop    d
    pop    d
    jmp    begin

;        The following instruction is used to call the initial
;    entry via HL.

dopchl:    pchl

    ENDFUNC    corstart



    FUNCTION    corpass ;(fcv, passval)
    EXTERNAL    corwmip

;        This function does all the "dirty work" needed to get
;    from one coroutine to another.  It maintains the "who-am-I" and
;    "passer" linkages, saves register content from one invocation to
;    the next, and does the reloading of the stack pointer and the
;    transfer of control.

;    First, save the BC register of the departing coroutine:

    push    b

;    Get a pointer to the memory location in which the WMI pointer
;    resides (BC) and to the current FCV (DE).

    call    corwmip
    mov    b,h
    mov    c,l
    mov    e,m
    inx    h
    mov    d,m

;    Save the current stack pointer at Cf$stkptr$ in the current FCV.
;    The stack looks like:
;        +0    BC register storage
;        +2    Return address
;        +4    Target FCV
;        +6    Passed value

    lxi    h,0
    dad    sp
    xchg
    mov    m,e
    inx    h
    mov    m,d
    dcx    h
    xchg        ; FCV pointer back in DE.

;    Get a pointer to target coroutine in HL

    lxi    h,4
    dad    sp
    mov    a,m
    inx    h
    mov    h,m
    mov    l,a

;    Set the "passer" word in the target to designate the source.

    inx    h        ; Passer is at relative location 2
    inx    h
    mov    m,e
    inx    h
    mov    m,d
    dcx    h
    dcx    h
    dcx    h

;    Set the WMI linkage to the target coroutine:

    mov    a,l
    stax    b        ; WMI is still in BC
    inx    b
    mov    a,h
    stax    b
    xchg            ; Target FCV now in DE.

;    Get the passed value:

    lxi    h,6
    dad    sp
    mov    a,m
    inx    h
    mov    h,m
    mov    l,a
    xchg            ; DE = passed value; HL=target FCV

;    Reload the stack pointer from the target FCV

    mov    a,m
    inx    h
    mov    h,m
    mov    l,a
    sphl

;    Put the passed arg in HL, restore the BC register, and go back
;    to the target coroutine's saved return address.

    xchg
    pop    b
    ret

    ENDFUNC    corpass



    FUNCTION    corwmip
    EXTERNAL    fprintf, exit

;        This function contains the static storage used by the
;    coroutine package.  It also has the code that handles the case
;    where the main coroutine (or one which has been RESUMEd by it)
;    has tried to DETACH.

;    When we're called, return pointer to the word inmemory where
;    the WMI linkage is stored:

    lxi    h,wmiptr
    ret

;    First static area is the WMI linkage:

wmiptr:    dw    mainfcv        ; Initially, main coroutine running.

;    Then comes the main coroutine's FCV:
;    *** SBRK depends on this following WMIP; don't change it...

mainfcv:
    ds    2    ; Space for stack pointer
    dw    falloff    ; Passer -- dumy "falloff" FCV
    dw    falloff ; Caller
    dw    0    ; Type is unknown.
    dw    -8    ; Stack size is ridiculous.
    dw    0    ; User info is zero.

;     Next is a dummy FCV for the "falloff" condition:

falloff:
    dw    fallstk    ; Stack pointer
    dw    falloff    ; Linked to self as caller
passer:    dw    falloff ; Linked to self as passer
    dw    0    ; Type is unknown
    dw    16    ; 6 bytes of stack space
    dw    0    ; User info word is 0

;    The "falloff" coroutine's stack follows:

    ds    12    ; Space for interrupt handler, JIC...
fallstk: dw    0    ; BC register save is unused.
    dw    mainend    ; Return address is "main end" procedure

;         The following code handles the problems
;    that arise when the main co-routine tries to return.  It
;    calls fprintf to display an error message, then exits.  It
;    can be modified by removing the call to exit() so that it
;    will continue the "main" coroutine instead.

mainend:
    lhld    passer        ; Who fouled up?
    shld    wmiptr        ; Whoever it was, re-enter it.

    mov    a,m        ; Restore the stack pointer of the
    inx    h        ; coroutine that fell off.
    mov    h,m
    mov    l,a
    sphl

    lhld    passer        ; Prepare passer ptr as 3rd arg to abort
    push    h

    lxi    h,message    ; Prepare error message pointer as 2nd arg
    push    h

    lxi    h, 4        ; Prepare unit 4 (STDERR) as the 1st arg

    call    fprintf ;(STD_ERR, message, passer)

    pop    b
    pop    b    ; Discard args
    pop    b

    call    exit        ; Quit

    pop    b    ;Get BC back
    ret            ; Resume the turkey

message:
    db    0AH, 'Attempt to detach a coroutine (FCV=0x%04x) which has'
    db    0AH, 'no caller linkage.'
    db    0

    ENDFUNC    corwmip
ed.
    dw    mainend    ;