Custom array of ports using array?

[Darrel Taylor]

It's not that it's OK to "Be interrupted", but it's OK to be in the routine that does the interrupting.

PAUSEUS has a couple shortcomings. One, is that it uses PBP's system variables (R0-R8). So it corrupts PBP's flow if it's used in an ASM interrupt without "Instant Interrupts".

The second is that PAUSEUS has a minimum delay of around 24us @ 4mhz since it figures out the delay Count at run time.

The DelayUS macro can pause for a little as 1us by calculating the delay at Compile Time, and adding a single NOP if that's all that's needed. Or a 3cycle loop and 2 NOP's if running at 20mhz. And it doesn't use any PBP system vars.

It can be useful in other programs as well, so I'll show it here again for those that aren't as diligent as you Steve.

VP_DelayCount  VAR WORD BANK0  ; Used for DelayUS only

ASM
;----[Similar to PAUSEUS, but ASM interrupt compatible]---(accurate to 1uS)--
DelayUS  macro T
  local InstCount, LoopCount, DelayLoop, LoopsDone, LeftOver, Offset
; -- Calculate number of 3 cycle loops plus leftover nop's to execute --
InstCount = ((OSC*10/4)*T+5)/10 ; Inst cycles required for delay (Rounded UP)
LoopCount = InstCount / 3
    if (LoopCount > 255)
Offset = (LoopCount >> 8) * 7 + 4
    else
Offset = 0
    endif
; -- Adjust for HighByte --
InstCount = InstCount - Offset
    if (Offset > (LoopCount & 0FFh))
InstCount = InstCount - 4
    endif
LoopCount = InstCount / 3
    if (LoopCount > 255)
Offset = (LoopCount >> 8) * 7
    else
Offset = 0
    endif
LeftOver  = InstCount % 3
;-------------------------------------------
    if (LoopCount > 0)
        MOVE?CW  LoopCount, _VP_DelayCount
DelayLoop
        decfsz   _VP_DelayCount, F               ;  1
        goto     DelayLoop                       ;  2   3 per loop, under 256
    
        if (LoopCount > 255)
            movf     _VP_DelayCount + 1, W       ;  1    
            btfsc    STATUS, Z                   ;  1    
            goto     LoopsDone                   ;  2   4 on last loop
            
            decf     _VP_DelayCount + 1, F       ;  1    
            goto     DelayLoop                   ;  2   7 per highbyte count 
LoopsDone
        endif
    endif
    if (LeftOver > 0)
        nop
    endif
    if (LeftOver > 1)
        nop
    endif
  endm
ENDASM

[SteveB]

Ok,

It's not that it's OK to "Be interrupted", but it's OK to be in the routine that does the interrupting.

This makes much more sense than what I was thinking.

On thing that should be mentioned. It is generally best to keep interrupt service routines (ISR) as short as possible, so that additional interrupts are not "missed" while handling the current interrupt. So putting a pause into an ISR must be used with caution, and with a good understanding of how it will effect other timing related items. One exception to this would be the 16-bit PICs with High and Low priority interrupts (which are supported by PBP), where a pause in a low prority interrupt would not prevent a high priority interrupt from executing. So all the time critical inturrupts could be High Priority.

Steve