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// See LICENSE for license details.
// This demo shows how to use basic
// RISC-V profiling counters, mcycle
// (counts the number of processor cycles)
// and minstret (counts the number of retired instructions).
// Note that both are writable as well.
#include <stdio.h>
// The CSR encodings are in this header.
#include "encoding.h"
// The mcycle counter is 64-bit counter, but since
// Freedom E platforms use RV32, we must access it as
// 2 32-bit registers. At 256MHz, the lower bits will
// roll over approx. every 5 seconds, so we check for
// rollover with this routine as suggested by the
// RISC-V Priviledged Architecture Specification.
#define rdmcycle(x) { \
uint32_t lo, hi, hi2; \
__asm__ __volatile__ ("1:\n\t" \
"csrr %0, mcycleh\n\t" \
"csrr %1, mcycle\n\t" \
"csrr %2, mcycleh\n\t" \
"bne %0, %2, 1b\n\t" \
: "=r" (hi), "=r" (lo), "=r" (hi2)) ; \
*(x) = lo | ((uint64_t) hi << 32); \
}
// The minstret counter is 64-bit counter, but
// Freedom E platforms use RV32, we must access it as
// 2 32-bit registers, same as for mcycle.
#define rdminstret(x) { \
uint32_t lo, hi, hi2; \
__asm__ __volatile__ ("1:\n\t" \
"csrr %0, minstreth\n\t" \
"csrr %1, minstret\n\t" \
"csrr %2, minstreth\n\t" \
"bne %0, %2, 1b\n\t" \
: "=r" (hi), "=r" (lo), "=r" (hi2)) ; \
*(x) = lo | ((uint64_t) hi << 32); \
}
// Simple program to measure the performance of.
int factorial(int i){
int result = 1;
for (int ii = 1; ii <= i; ii++) {
result = result * i;
}
return result;
}
int main()
{
uint64_t before_cycle;
uint64_t before_instret;
uint64_t after_cycle;
uint64_t after_instret;
printf("\n\nDemo 1: Using Counter Differences.\n");
for (int ii = 0; ii < 3; ii++){
rdmcycle(&before_cycle);
rdminstret(&before_instret);
volatile int result = factorial (100);
rdmcycle(&after_cycle);
rdminstret(&after_instret);
printf("Loop %d: Retired %d instructions in %d cycles\n",
ii,
(uint32_t)(after_instret - before_instret),
(uint32_t)(after_cycle - before_cycle));
}
printf("\n\nDemo 2: Clearing Counters, Using Values Directly.\n");
for (int ii = 0; ii < 3; ii++){
write_csr(mcycle, 0);
write_csr(mcycleh, 0);
write_csr(minstret, 0);
write_csr(minstreth, 0);
volatile int result = factorial (100);
rdmcycle(&after_cycle);
rdminstret(&after_instret);
printf("Loop %d: Retired %d instructions in %d cycles\n",
ii,
(uint32_t)(after_instret),
(uint32_t)(after_cycle));
}
return 0;
}
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