Re: Theorizing: what can be done with DOT clock signal present on C64 expansion port?

> On 04/11/2021 19:46, Claudio Sánchez wrote:
>> This would work as "send data to an external sound processor with its
>> own memory and let it do the work". The dot clock would allow for
>> internal upsampling or extra DSP effects that the SID wouldn't be able
>> to do and would be too expensive to do in software by the CPU.
>>

> What external sound processor and what data? If you want to send MP3
> then the DOT clock is too low, if you want to send ADPCM then the DOT
> clock is too high.

Well... Not everything is digital sound. One thing for example could be an external HQ sound generator chip, that could be based on wavetable synthesis, that would work as the SID does, receiving just data of the notes to be played and which sounds to produce. It could use the DOT clock for its own inner workings.

Another thing could be a sound DSP that could modify the SID sound (if anyone would want to do that!!) by getting that sound from the C64 output and then processing it as instructed by registers.

If needed, the DSP processor could do the reverse way: processing audio or video that would be digitized by dedicated chips and putting that already processed data in the right audio or video format to the main memory. The CPU is just too slow for that. What for? well... it can be done, right?


> 
>> The ability of doing DMA from outside would be helpful so the CPU
>> would ask for certain calculations to be done by the external math
>> coprocessor by presetting certain memory locations with both the
>> operations and the data to be processed, and then asking the external
>> chip to do them. Things like 3D games, database applications,
>> spreadsheets, graphics suites... would benefit from it.
>>
> You wouldn't use the DOT clock for DMA though.

Yes, de DOT clock wouldn't be used for DMA -- I think the phi2 would.

I think you misunderstand what the DOT clock is.

I'd like to learn actually, and that's why this post is called "theorizing". I saw that signal available to external expansion and thought that being in sync with what the VIC-II receives, it could be used to run hardware that would allow the machine to do things that are too slow when done in software.
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