[phx]

Nice example.

Although in a real program you should avoid to save and restore registers which don't change. This wastes a lot of time each interrupt:

myTimerInterrupt:
    ;tst.w    8(a1)
    ;beq.b    .exit
    movem.l    d2-d7/a2-a6,-(sp)
    add.l    #1,t10ms
    movem.l    (sp)+,d2-d7/a2-a6
    moveq    #1,d0
.exit:
    rts

Originally Posted by xArtx

I assume because both chips are driven by the same clock,
that those two timers can't go out of sync?

Yes. All timers use the same 02 clock (0.7 MHz). Alternatively you can let the timers count positive CNT transitions on the serial port. And timer B can also count timer A underflows.