base:efficient_tod_initialisation
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| base:efficient_tod_initialisation [2019-05-17 12:58] – [Dual purpose] silverdr | base:efficient_tod_initialisation [2019-05-20 11:45] – [Proper solution] silverdr | ||
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| which correspond to the four possible C64 hardware setup combinations. Comparing to $51, which falls more or less in the middle, gives us the expected answer. If the HI byte of the timer has value higher than $51 we have 60Hz supplied to the TOD pin. If OTOH it has lower value, we have 50Hz supplied. | which correspond to the four possible C64 hardware setup combinations. Comparing to $51, which falls more or less in the middle, gives us the expected answer. If the HI byte of the timer has value higher than $51 we have 60Hz supplied to the TOD pin. If OTOH it has lower value, we have 50Hz supplied. | ||
| + | |||
| + | Advantages: | ||
| + | * Does not break on Super-CPU and similar | ||
| + | * No screen side-effects | ||
| + | * Short and fast | ||
| Please also note that we use CIA #2 and not CIA #1. CIA #2 is chosen because changing the timer values there does not affect regular IRQ timings. Moreover, KERNAL re-initialises those timers whenever it wants to use them. This saves as a few bytes, which would otherwise be needed to save and restore timer registers' | Please also note that we use CIA #2 and not CIA #1. CIA #2 is chosen because changing the timer values there does not affect regular IRQ timings. Moreover, KERNAL re-initialises those timers whenever it wants to use them. This saves as a few bytes, which would otherwise be needed to save and restore timer registers' | ||
base/efficient_tod_initialisation.txt · Last modified: 2020-10-27 02:31 by silverdr