Ariane Performance Measures

[jthoma]

Hi,

i am trying to do some performance measurements on the Ariane processor and therefore, I would like to use the cycle count from the RDCYCLE instruction. My code compiles fine, however, if I run it, I get a “illegal instruction” error. The following is the critical code snippet (both the CSRRS and RDCYCLE lead to the same error)

Code:

unsigned long get_clk(){
    unsigned long timer = 0;
    //__asm__ volatile("CSRRS %[result], cycle, x0\n\t" : [result]"=r"(timer)::);
    __asm__("RDCYCLE %[result]\n\t" : [result]"=r"(timer)::);
    return timer;
}

The RISC-V “Instruction Set Manual II: Privileged Architecture” states that the cycle CSR entry should be readable from user mode. I figured that this might not be the case in Ariane which would be fine if I could get to supervisor mode somehow. I looked into writing a kernel module that would give me access to the performance measures. Unfortunately, this turned out to be quite challenging since I can neither compile code on the FGPA nor use insmod to install my kernel module. Is there an easy way to get access to the cycle timer?

Thank you!

Jan

-- Edit: The same happens if I just use the built-in C time() function...