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base:efficient_tod_initialisation

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base:efficient_tod_initialisation [2019-05-17 12:58] – [Dual purpose] silverdrbase:efficient_tod_initialisation [2020-01-31 17:49] – [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.
  
-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. MoreoverKERNAL 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' original values. Last and least we do not disable NMIs as it is assumed that checking/setting the params will be done as part of application initialisation, before setting up IRQ/NMI handlers.+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 it timers are by default not used by the system. Moreover KERNAL initialises those timers according to its needs, whenever it wants to use them. This saves us a few bytes, which would otherwise be needed to preserve original settings. Last and least we do not disable NMIs as it is assumed that checking/setting the params will be done as part of application initialisation, before any IRQ/NMI handlers are set.
 ===== Dual purpose ===== ===== Dual purpose =====
 I mentioned before that this routine can serve also another purpose and give us potentially even more savings. Yes, with addition of only a few bytes: I mentioned before that this routine can serve also another purpose and give us potentially even more savings. Yes, with addition of only a few bytes:
base/efficient_tod_initialisation.txt · Last modified: 2020-10-27 02:31 by silverdr