add PICO_DIVIDER_DISABLE_INTERRUPTS flag which makes PICO_DIVIDER disable interrupts around division rather than using co-operative guards to protect nested use (i.e. within IRQ/exception). Use of this flag can simplify porting of RTOSes but with a different performance profile (#372)

test/pico_divider_test/pico_divider_nesting_test.c

@@ -0,0 +1,142 @@
+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include "pico/stdlib.h"
+#include "hardware/dma.h"
+#include "hardware/irq.h"
+
+volatile bool failed;
+volatile uint32_t count[3];
+volatile bool done;
+
+bool timer_callback(repeating_timer_t *t) {
+    count[0]++;
+    static int z;
+    for (int i=0; i<100;i++) {
+        z += 23;
+        int a = z / 7;
+        int b = z % 7;
+        if (z != a * 7 + b) {
+            failed = true;
+        }
+    }
+    return !done;
+}
+
+void do_dma_start(uint ch) {
+    static uint32_t word[2];
+    assert(ch < 2);
+    dma_channel_config c = dma_channel_get_default_config(ch);
+    // todo remove this; landing in a separate PR
+#ifndef DREQ_DMA_TIMER0
+#define DREQ_DMA_TIMER0 0x3b
+#endif
+    channel_config_set_dreq(&c, DREQ_DMA_TIMER0);
+    dma_channel_configure(ch, &c, &word[ch], &word[ch], 513 + ch * 23, true);
+}
+
+void test_irq_handler0() {
+    count[1]++;
+    dma_hw->ints0 |= 1u;
+    static uint z;
+    for (int i=0; i<80;i++) {
+        z += 31;
+        uint a = z / 11;
+        uint b = z % 11;
+        if (z != a * 11 + b) {
+            failed = true;
+        }
+    }
+    if (done) dma_channel_abort(0);
+    else      do_dma_start(0);
+}
+
+void test_irq_handler1() {
+    static uint z;
+    dma_hw->ints1 |= 2u;
+    count[2]++;
+    for (int i=0; i<130;i++) {
+        z += 47;
+        uint a = z / -13;
+        uint b = z % -13;
+        if (z != a * -13 + b) {
+            failed = true;
+        }
+        static uint64_t z64;
+        z64 -= 47;
+        uint64_t a64 = z64 / -13;
+        uint64_t b64 = z64 % -13;
+        if (z64 != a64 * -13 + b64) {
+            failed = true;
+        }
+    }
+    if (done) dma_channel_abort(1);
+    else      do_dma_start(1);
+}
+
+void test_nesting() {
+    uint z = 0;
+
+    // We have 3 different IRQ handlers, one for timer, two for DMA completion (on DMA_IRQ0/1)
+    // thus we expect re-entrancy even between IRQs
+    //
+    // They all busily make use of the dividers, to expose any issues with nested use
+
+    repeating_timer_t timer;
+    add_repeating_timer_us(529, timer_callback, NULL, &timer);
+    irq_set_exclusive_handler(DMA_IRQ_0, test_irq_handler0);
+    irq_set_exclusive_handler(DMA_IRQ_1, test_irq_handler1);
+
+    dma_set_irq0_channel_mask_enabled(1u, true);
+    dma_set_irq1_channel_mask_enabled(2u, true);
+    dma_hw->timer[0] = (1 << 16) | 32; // run at 1/32 system clock
+
+    irq_set_enabled(DMA_IRQ_0, 1);
+    irq_set_enabled(DMA_IRQ_1, 1);
+    do_dma_start(0);
+    do_dma_start(1);
+    absolute_time_t end = delayed_by_ms(get_absolute_time(), 2000);
+    int count_local=0;
+    while (!time_reached(end)) {
+        for(uint i=0;i<100;i++) {
+            z += 31;
+            uint a = z / 11;
+            uint b = z % 11;
+            if (z != a * 11 + b) {
+                failed = true;
+            }
+        }
+        count_local++;
+    }
+    done = true;
+    cancel_repeating_timer(&timer);
+    printf("%d: %d %d %d\n", count_local, (int)count[0], (int)count[1], (int)count[2]);
+
+    // make sure all the IRQs ran
+    if (!(count_local && count[0] && count[1] && count[2])) {
+        printf("DID NOT RUN\n");
+        exit(1);
+    }
+    if (failed) {
+        printf("FAILED\n");
+        exit(1);
+    }
+}
+
+int main() {
+#ifndef uart_default
+#warning test/pico_divider requires a default uart
+#else
+    stdio_init_all();
+#endif
+    test_nesting();
+    printf("PASSED\n");
+    return 0;
+}
+