[Coco] double speed poke ...

[KnudsenMJ at aol.com]

In a message dated 4/27/05 5:17:58 PM Eastern Daylight Time,  
robert.gault at worldnet.att.net writes:

>In  my own experience with a Coco1, there was no necessity to synchronize  
>a sta $FFD6. Further the address dependent and full memory speed  
>changes, either direction, could be used at any time. The product  sheet 
>states a specific sequence should be  used.



I did a lot of BASIC and assembly work with the Fast and Half-Fast speed  
pokes, and always observed the rule that, when going between Normal (Slow) and  
Fast (white-out screen, no RAM refresh), you always hit the Half-Fast (doubled  
on ROM access) Mode in between.
 
Since that was just one extra POKE or STA, it never bothered me to do  it.  
No other ops or synching is needed.
 
As far as I could tell, the effect was instantaneous.
 
My hybrid programs (BASIC and machine code) were written to drop back to  
Normal speed before doing tape or disk I/O.
BTW, when running Fast mode, you can guarantee RAM refresh in a machine  code 
routine by running a loop that's at least 256 bytes long.  You may  have to 
duplicate (unroll) a loop a few times to make it that big.  I did  this for 
music synthesis and never lost a bit of RAM.
 
Speed POKEs are easy to use and safe if you follow the guidelines.
--Mike K.