ncoplin_at_orbeng.com
Date: 2003-08-19 10:24:00
Hello Ruud.
> So if I understand you correctly, the SCPU starts up in a > mode where
reading is done at full speed from its own
> memory and writing is done at 1 MHz to both the systems. > The speedgain
lays in the fact that normally there are more > reads then writes to be
done. (horrible translation IMHO) > More speed can be gained by windowing
the RAM-area
> running the risk that graphics disapear or never show.
[COPLIN, Nicholas.]
Not quite. The SCPU has a "1 byte" cache. When the 65816 writes a byte, it
gets written to the SCPUs RAM at the running speed, and to the CPLD (a big
one) which has a 1byte cache (should be called a latch/buffer, but CMD
called it a cache). This 1byte is synchronised and written to the C64. As
such, on sustained writes, operation is about 4MHz as some internal cycles
(instruction reads) can still occur on the 65816 and it only gets held up
when it tries to write the next byte. If you set for mirror-NONE, the
graphics will not get updated as the CPLD will not latch the byte to write
to the C64.
And yes... when a badline occurs the write cycle can be held off for up to
the full 43us.
- Nick
- Nick
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