Initial Release

timer/timer_lowlevel/CMakeLists.txt

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+if (PICO_ON_DEVICE)
+    add_executable(timer_lowlevel
+            timer_lowlevel.c)
+
+    # Disable SDK alarm support for this lowlevel example
+    set(PICO_TIME_DEFAULT_ALARM_POOL_DISABLED 1)
+
+    target_link_libraries(timer_lowlevel pico_stdlib)
+
+    # create map/bin/hex file etc.
+    pico_add_extra_outputs(timer_lowlevel)
+
+    # add url via pico_set_program_url
+    example_auto_set_url(timer_lowlevel)
+endif ()

timer/timer_lowlevel/timer_lowlevel.c

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+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include "pico/stdlib.h"
+#include "hardware/timer.h"
+#include "hardware/irq.h"
+
+/// \tag::get_time[]
+// Simplest form of getting 64 bit time from the timer.
+// It isn't safe when called from 2 cores because of the latching
+// so isn't implemented this way in the sdk
+static uint64_t get_time(void) {
+    // Reading low latches the high value
+    uint32_t lo = timer_hw->timelr;
+    uint32_t hi = timer_hw->timehr;
+    return ((uint64_t) hi << 32u) | lo;
+}
+/// \end::get_time[]
+
+/// \tag::alarm_standalone[]
+// Use alarm 0
+#define ALARM_NUM 0
+#define ALARM_IRQ TIMER_IRQ_0
+
+// Alarm interrupt handler
+static volatile bool alarm_fired;
+
+static void alarm_irq(void) {
+    // Clear the alarm irq
+    hw_clear_bits(&timer_hw->intr, 1u << ALARM_NUM);
+
+    // Assume alarm 0 has fired
+    printf("Alarm IRQ fired\n");
+    alarm_fired = true;
+}
+
+static void alarm_in_us(uint32_t delay_us) {
+    // Enable the interrupt for our alarm (the timer outputs 4 alarm irqs)
+    hw_set_bits(&timer_hw->inte, 1u << ALARM_NUM);
+    // Set irq handler for alarm irq
+    irq_set_exclusive_handler(ALARM_IRQ, alarm_irq);
+    // Enable the alarm irq
+    irq_set_enabled(ALARM_IRQ, true);
+    // Enable interrupt in block and at processor
+
+    // Alarm is only 32 bits so if trying to delay more
+    // than that need to be careful and keep track of the upper
+    // bits
+    uint64_t target = timer_hw->timerawl + delay_us;
+
+    // Write the lower 32 bits of the target time to the alarm which
+    // will arm it
+    timer_hw->alarm[ALARM_NUM] = (uint32_t) target;
+}
+
+int main() {
+    stdio_init_all();
+    printf("Timer lowlevel!\n");
+
+    // Set alarm every 2 seconds
+    while (1) {
+        alarm_fired = false;
+        alarm_in_us(1000000 * 2);
+        // Wait for alarm to fire
+        while (!alarm_fired);
+    }
+}
+
+/// \end::alarm_standalone[]