Re: JIffyDOS Coding

From: Nicolas Welte (
Date: 2001-03-28 09:48:37 wrote:
> It looks like the following snippet is the key part of the JD routine, which
> reads in data as bit-pairs every 10us. The trick of course is if this is to
> be replicated for a VIC20 or C16/Plus4 then the data needs to be processed
> in this relatively short time as there is no hand-shaking to hold off the
> 1541 once the Ok for the byte send has been initiated. Also, data is sent as
> 254byte packets... between pauses.

Pauses? Maybe these pauses are used to work around the badlines on the 64?
Somehow a 40us badline and a 10us timing don't work well together if the
routine doesn't know when to expect a badline. The same could be used to work
around badlines on the 264 series, only that you need a longer Pause (two
badlines, I think), which will make the overall transfer speed slower. On the
64 ususally Sprites are switched off during fastloading to avoid extra memory
accesses, but I don't know about Jiffy. Does the TED have any memory accesses
except for video matrix and attributes, and refresh, of course? 

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