Posted By
crock
on 2011-12-20
05:36:07
 |  Re: Can someone run this on genuine NTSC hardware?
Wow - those numbers really surprise me.
They represent the number of interrupts that have occurred during the time it takes to execute a simple nested loop, which based on my math, lasts for 525353 cycles. The first line is with TED forced into single clock mode and the second with the screen blanked and thus in 2 x clock.
From left to right, the numbers are the number of interrupts that occurred with:
1) Timer 1 initialized with a reload value of $2000
2) Timer 2 initialized with a value of $0100 (remembering that it reloads with $ffff)
3) Timer 3 initialized with a value of $ff00 (remembering that it reloads with $ffff)
4) Raster interrupts
On an NTSC machine, a slightly different number of raster interrupts makes sense, and timers 2 and 3 are the same, but I cannot explain why timer1 is so radically different, ie. by about 50%!!
My understanding was that the TED timers are decremented at the clock speed so I would have expected the figures to be very similar if not identical between NTSC and PAL.
@TLC - is this machine modded in any way (either ROM or hardware, excluding your oscillator mod), any add on hardware that could be generating additional interrupts?
Any theories appreciated....
Rob
edit : 64tass source - http://inchocks.co.uk/c64/timer.asm
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