Scratchspace size limitations

[Kylee Michelle Krzanich]

I'm working on a tapeout right now and there's some severe area limitations especially for the memory macros. We've completely removed the L2 and we have the L1 functioning with about 5KB total space.  I would like to reduce the scratchpad size but none of our programs run without at least 16KB of scratchpad. Is it possible to lower the size or no? 

Thanks for your help!

[Kylee Michelle Krzanich]

Just to clarify, it won't even boot completely (the RAM monitor gives a fatal error) when the scratchpad size is lowered. 

[Jerry Zhao]

There's nothing preventing you from building a system with less than a kilobyte of on-chip memory in L1 and L2.
Whether such a system is suitable for your use case, depends on your use case.

If a monitor is throwing that assertion, it means some device is trying to access invalid physical memory. You should trace down exactly what hardware/software is causing this. Perhaps there is a simple software fix.

If you are using L1 DCache as scratchpad, and that is the bulk of the memory in your system, you should make sure the DCache is configured as direct-mapped. IIRC, only a single way of the cache can be used as scratchpad.

-Jerry

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[Jiuyang Liu]

Are we talking about the Rocket D$? I thought the limitation is you cannot use last way as scratchpad?

IIRC if you write the scratchpad of last way, it will allocate scratchpad form D$, or deallocate it with writing a 0 to this address.

Jiuyang

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