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Please express true isa as RV32IMAZicsr_Zifencei #15
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Please be more specific about what is needed? Keep in mind this is a single-core hart + there is no memory ordering constraints as everything happens synchronously. Do you have any tests I can test against? I have considered also reducing functionality of A to |
Documentation.
There are none as there is only one CPU. |
also idk if u know this but you can have GCC emulate multiplication and just omit the M extension. there is also an option in BR to do so. |
I am aware of this, but it added to the complexity significantly for the targets where I could do that and I couldn't figure out how to build the kernel against RV32IA using buildroot. I will need to do more research to really understand RV32A. I still don't actually understand how it works. It would be "nice" to make it actually atomic. |
Tbh I'm impressed it works without it but nice to know it's not actually necessary in practice. |
I mean I Would like to add proper support, at least for |
Go look at libgcc it's what implements multiplication when there is no hw multiplier. Look in the gcc root gcc/libgcc/config/riscv/atomic.c |
I guess I don't understand what it is overall you are recommending I do? |
Just add documentation of the caveats I explained. If you want to fix the caveats you can refer to my last post. Or just document them. You should also explained what you did with the fence and friends instructions. |
What I'm trying to explain is I still don't understand how what I've done is different from how it should be. I can't really document what I don't understand. |
I just reread the spec in that section again. Would a good approach be to, inside the emulator, emulate the AMOs as other atomics. I.e. make them appear as |
For the time being, I've added the following note: †: Zifence+RV32A are stubbed. So, tweaks will need to be made if you want to emulate a multiprocessor system with this emulator. |
That's fine I don't understand it well either. Just a general explanation that they are not to spec. Which you have done now! |
If you want this will make Linux without M extension and also shortens both the defconfigs |
@Mr-Bossman how long does boot take? How big is your kernel image? |
Ignore the file ext. |
Wow that's really impressive. I didn't think that would be possible w/o M. |
its very much a hack lol |
This is RV32IMAZicsr_Zifencei.
you should also note that the atomics are non-atomic operations and are used for bit manipulation.
Base Integer Instruction Set, 32-bit | 40
Standard Extension for Integer Multiplication and Division | 8
Standard Extension for Atomic Instructions | 11
Control and Status Register (CSR) | 6
Instruction-Fetch Fence | 1
totaling in 66 instructions
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