flash_cache_perfctr.c

/**
 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <stdio.h>
#include <stdlib.h>

#include "pico/stdlib.h"
#include "hardware/structs/xip_ctrl.h"

// Example of using cache hit/access counters, and showing the effect of
// invalidate on cache miss/hit.


const uint32_t test_data[8] = {0, 1, 2, 3, 4, 5, 6, 7};

void __no_inline_not_in_flash_func(check)(bool cond, const char *msg) {
    if (!cond) {
        puts(msg);
        exit(-1);
    }
}

void __no_inline_not_in_flash_func(check_hit_miss_invalidate)() {
    io_rw_32 *test_data_ptr = (io_rw_32 *) test_data;

    /// \tag::check_hit_miss_invalidate[]
    // Flush cache to make sure we miss the first time we access test_data
    xip_ctrl_hw->flush = 1;
    while (!(xip_ctrl_hw->stat & XIP_STAT_FLUSH_READY_BITS))
        tight_loop_contents();

    // Clear counters (write any value to clear)
    xip_ctrl_hw->ctr_acc = 1;
    xip_ctrl_hw->ctr_hit = 1;

    (void) *test_data_ptr;
    check(xip_ctrl_hw->ctr_hit == 0 && xip_ctrl_hw->ctr_acc == 1,
          "First access to data should miss");

    (void) *test_data_ptr;
    check(xip_ctrl_hw->ctr_hit == 1 && xip_ctrl_hw->ctr_acc == 2,
          "Second access to data should hit");

    // Write to invalidate individual cache lines (64 bits)
    // Writes must be directed to the cacheable, allocatable alias (address 0x10.._....)
    *test_data_ptr = 0;
    (void) *test_data_ptr;
    check(xip_ctrl_hw->ctr_hit == 1 && xip_ctrl_hw->ctr_acc == 3,
          "Should miss after invalidation");
    (void) *test_data_ptr;
    check(xip_ctrl_hw->ctr_hit == 2 && xip_ctrl_hw->ctr_acc == 4,
          "Second access after invalidation should hit again");
    /// \end::check_hit_miss_invalidate[]
}

// Some code which achieves a very high cache hit rate:
int recursive_fibonacci(int n) {
    if (n <= 1)
        return 1;
    else
        return recursive_fibonacci(n - 1) + recursive_fibonacci(n - 2);
}

int main() {
    stdio_init_all();

    uint hit = xip_ctrl_hw->ctr_hit;
    uint access = xip_ctrl_hw->ctr_acc;

    if (access == 0)
        printf("It looks like you're running this example from SRAM. This probably won't go well!\n");

    // Note the hit rate will appear quite low at boot, as the .data,
    // .time_critical init in crt0 read a lot of read-once data from flash
    printf("At boot: %d hits, %d accesses\n", hit, access);
    printf("Hit rate so far: %.1f%%\n", hit * 100.f / access);

    printf("Calculate 25th fibonacci number: %d\n", recursive_fibonacci(25));
    uint32_t ctr_hit = xip_ctrl_hw->ctr_hit;
    uint32_t ctr_acc = xip_ctrl_hw->ctr_acc;
    printf("New hit rate after printf and fibonacci: %.1f%%\n", ctr_hit * 100.f / ctr_acc);

    check_hit_miss_invalidate();

    printf("Hit/miss check passed\n");
    return 0;
}