[Coco] Hook an IRQ in CMOC?

[Pierre Sarrazin]

Hi Randy,

Dixit Randy Weaver (2017-11-08 06:51):
> Are their any examples of hooking an IRQ to a CMOC function?

Here is one. First, define the service routine using the "interrupt"
keyword, and use certain ports to test that the IRQ is due to the 60
Hz timer:

    interrupt void irqISR()
    {
        if ((* (char *) 0xFF03) & 0x80)  // do nothing if 63.5 us interrupt
        {
            // 60 Hz interrupt. Reset PIA0, port B interrupt flag.
            * (char *) 0xFF02;

            // Do something that needs to be done every 60th of a second.
        }
    }

Then, install that function as the IRQ handler:

    #include <coco.h>

    [...]

    disableInterrupts();
    byte *isr = * (byte **) 0xFFF8;
    *isr = 0x7E;  // JMP extended
    * (void **) (isr + 1) = irqISR;
    enableInterrupts();

Inline assembly can be used if more efficiency is needed.

This and other topics are covered in the manual:
http://sarrazip.com/dev/cmoc-manual.html
http://sarrazip.com/dev/cmoc.html

-- 
Pierre Sarrazin <sarrazip @ sarrazip . com>