Temporary central repository of Darrel Taylor's works (including Mr E's Multicalc)

[Darrel Taylor]

<table cellpadding=6><tr><td valign=center></td><td>The Instant Interrupt System consists of several "Layers".

The Bottom Layer is "DT_INTS-14.bas". This file contains everything required to use Interrupts at the ASM level. &nbsp; It handles all of the "Context Saving/Restoring", detects which interrupt has been triggered, and calls the appropriate "User Routine".

The next layer up is created from the INT_LIST macro you define in the program. &nbsp; It defines the Interrupt sources to use and the corresponding subroutines that will be called. &nbsp; They can be either simple subroutines, or complete "Modules" in a separate Include file, like the Elapse Timer. &nbsp; Up to 14 separate INT_Handler's can be in the LIST.

And, the Top Layer is the normal PBP program that runs in the foreground.

If Basic Laguage interrupts are not being used, then DT_INTS-14.bas is the only file you need to include.</td></tr></table>Here's another example of a Blinky Light program using TMR1 with an Assembly Language Interrupt handler

LED1   VAR  PORTD.0
LOW  LED1                    ; Set to Output Low

INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   ToggleLED1,   ASM,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor

    INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts  
ENDASM

T1CON = $31                  ; Prescaler=8, TMR1ON

Main:
    PAUSE 1
GOTO Main

'---[TMR1_INT - interrupt handler]------------------------------------------
ASM
ToggleLED1
    btfsc  _LED1
    goto   $+3
    bsf    _LED1
    goto   $+2
    bcf    _LED1
    INT_RETURN
ENDASM

<font size=-3>Code Size = 104 Words</font>

Notice that the INT_Handler's Type is ASM, and the Label does not have an underscore before it.<hr><table cellpadding=6><tr><td></td><td valign=top>By using this type of Layering scheme. It allows us more flexability, depending on the type of interrupt we want to use. &nbsp; If we want to add Basic Language Handlers, all we need to do is Include "ReEnterPBP.bas", and it will insert another Layer in-between the Base and the Handlers.

With this layer included, you can have any combination of ASM and PBP interrupts in the same program</td></tr></table>
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[Darrel Taylor]

October 05, 2002 was a good day. &nbsp; Because that's the day that Tim Box released his "INT_CTRL.pbp" program. &nbsp; The original "Instant Interrupts"

Tim had discovered that the only reason you couldn't use Basic statements in a normal interrupt, was because the PBP system variables currently being used by the statement that got interrupted, would be overwritten by the Basic statements in the interrupt routine. &nbsp; And that, all you have to do is save the state of the system vars at the start of the interrupt, and restore them back to the way they were before exiting the interrupt and you can use any Basic statements you want.

I've probably said it too many times already but ... Thanks again Tim!
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ReEnterPBP.bas is an adaptation of the same concept, but it allows the Interrupt system to determine if it needs to save the variables or not.

For instance, if you have a program with both ASM and PBP interrupt handlers, and an interrupt triggers an ASM handler, there's no need to save the variables first, it would just be waisting valuable time. And if more than 1 Basic handler is triggered at the same time, it only saves the variables once, and processes all the Interrupts on the same pass, before restoring the system vars, again saving time.

However, it does still take a lot of time to save all those variables. Usually it takes around 70 instruction cycles to save the vars. Then another 70 cycles to restore them again. At 4mhz it's 140us total save and restore time, which limits the maximum interrupt frequency to just over 7khz. At 20mhz OSC, you can go up to almost 36khz. That's fast enough to receive RS232 at over 250Kbaud with the USART. &nbsp; But is still considerably slower than you can get with ASM interrupts.

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