Initial Release

flash/cache_perfctr/flash_cache_perfctr.c

@@ -0,0 +1,88 @@
+/**
+ * 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));
+    printf("New hit rate after printf and fibonacci: %.1f%%\n", xip_ctrl_hw->ctr_hit * 100.f / xip_ctrl_hw->ctr_acc);
+
+    check_hit_miss_invalidate();
+
+    printf("Hit/miss check passed\n");
+    return 0;
+}