Number of ASIDs


#1

I am trying to find out the number of ASIDs supported by FU540 by writing ones to the ASID field of satp and then reading the field back. I am not sure if I did it correctly, but I always read back 0s from the ASID field on the Hifive unleashed board. Could someone let me know the number of ASIDs supported by FU540? If ASID support is not implemented, this means that we have to flush all TLB entries every time we change satp? If so, how many cycles are required to flush the TLB and how many cycles are required for a TLB refill?

Thanks!


(Paul Walmsley) #2

The CPU subsystem on the FU540 doesn’t support ASIDs.


#3

Hi Paul,

Thanks for confirming this. Do you know where I could find the cost for a TLB miss? Given that there are no ASIDs, the sfence.vma instruction simply invalidates all TLB entries, is that correct?

Thanks!