16h DP$WRDY wait on a timed semaphore
Input - none -
Output - none -
Description

Waits until the value in dpw_redy has been decremented to 0.

Each keyboard interrupt causes dpw_redy to be decremented by 1 and as such provides a handy 50 millisecond timer. However if interrupts are switched off this routine will still work as it recognises that interrupts are off and decrements dpw_redy once every 50 milliseconds.

Note that this routine behaves as a wait on a timed semaphore. It is used extensively by the LCD driver software to provide scrolling delays.

Example The following routine waits for 3 seconds
        LDD     #60
        STD     DPW_REDY
        OS      DP$WRDY
        RTS
Errors - none -