[FYI] variable count parameter retrieval

kuroneko · 2011-10-10 23:37

This is one more result of getting the [thread=134987]PASM-Gameduino-drivers[/thread] down in size (more a side effect actually). It's more concerned about speed than size so re-introduction may not be feasible. The parameter loop always fetches 8 parameters from hub (2 hub windows/long) regardless of whether they are needed or not.

movd    :arg, #arg0             ' get 8 arguments ; arg0 to arg7
        mov     t1, retaddr                             
        mov     t2, #8                                  
:arg    rdlong  0-0, t1
        add     :arg, d0
        add     t1, #4
        djnz    t2, #:arg

arg0    res     8

So I thought it should be possible to let each subroutine decide how many parameters are fetched. While this can be done in a loop it wouldn't get around the hub window issue (unless you go to more trouble than it's usually worth). The hub address of the first parameter is stored in retaddr, the address after the input array can be used for results. If no parameters are required then don't call the function. Otherwise simply use:

movi    retaddr, #%nnn_1      ' nnn: number of parameters -1 (0..7)
call    #args

The actual subroutine then uses cmpsub to increment the source address and generate an exit condition for us. Exit is done with an early (indirect) ret.

args            rdlong  arg0, retaddr           ' read 1st argument
                cmpsub  retaddr, delta wc       ' [increment address and] check exit
        if_nc   jmp     args_ret                ' cond: early return
        
                rdlong  arg1, retaddr           ' read 2nd argument
                cmpsub  retaddr, delta wc
        if_nc   jmp     args_ret

                rdlong  arg2, retaddr
                cmpsub  retaddr, delta wc
        if_nc   jmp     args_ret

                rdlong  arg3, retaddr
                cmpsub  retaddr, delta wc
        if_nc   jmp     args_ret

                rdlong  arg4, retaddr
                cmpsub  retaddr, delta wc
        if_nc   jmp     args_ret

                rdlong  arg5, retaddr
                cmpsub  retaddr, delta wc
        if_nc   jmp     args_ret

                rdlong  arg6, retaddr
                cmpsub  retaddr, delta wc
        if_nc   jmp     args_ret

                rdlong  arg7, retaddr
'               cmpsub  retaddr, delta wc
'       if_nc   jmp     args_ret

args_ret        ret

delta           long    %10 << 23 | $FFFC       '  %10  deal with movi setup
                                                ' -(-4) address increment