1 files changed, 70 insertions, 0 deletions
diff --git a/src/atsamd/samd51_timer.c b/src/atsamd/samd51_timer.c
new file mode 100644
index 00000000..60baf4f4
--- /dev/null
+++ b/src/atsamd/samd51_timer.c
@@ -0,0 +1,70 @@
+// SAMD51 timer interrupt scheduling
+//
+// Copyright (C) 2018-2019  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "board/irq.h" // irq_disable
+#include "board/misc.h" // timer_read_time
+#include "board/timer_irq.h" // timer_dispatch_many
+#include "internal.h" // enable_pclock
+#include "sched.h" // DECL_INIT
+
+// Set the next irq time
+static void
+timer_set(uint32_t value)
+{
+    TC0->COUNT32.CC[0].reg = value;
+    TC0->COUNT32.INTFLAG.reg = TC_INTFLAG_MC0;
+}
+
+// Return the current time (in absolute clock ticks).
+uint32_t __always_inline
+timer_read_time(void)
+{
+    // Need to request a COUNT update and then delay for it to be ready
+    TC0->COUNT32.CTRLBSET.reg = TC_CTRLBSET_CMD_READSYNC;
+    TC0->COUNT32.COUNT.reg;
+    TC0->COUNT32.COUNT.reg;
+    return TC0->COUNT32.COUNT.reg;
+}
+
+// Activate timer dispatch as soon as possible
+void
+timer_kick(void)
+{
+    timer_set(timer_read_time() + 50);
+}
+
+void
+timer_init(void)
+{
+    // Supply power and clock to the timer
+    enable_pclock(TC0_GCLK_ID, ID_TC0);
+    enable_pclock(TC1_GCLK_ID, ID_TC1);
+
+    // Configure the timer
+    TcCount32 *tc = &TC0->COUNT32;
+    irqstatus_t flag = irq_save();
+    tc->CTRLA.reg = 0;
+    tc->CTRLA.reg = TC_CTRLA_MODE_COUNT32;
+    NVIC_SetPriority(TC0_IRQn, 2);
+    NVIC_EnableIRQ(TC0_IRQn);
+    tc->INTENSET.reg = TC_INTENSET_MC0;
+    tc->COUNT.reg = 0;
+    timer_kick();
+    tc->CTRLA.reg = (TC_CTRLA_MODE_COUNT32 | TC_CTRLA_PRESCALER_DIV8
+                     | TC_CTRLA_ENABLE);
+    irq_restore(flag);
+}
+DECL_INIT(timer_init);
+
+// IRQ handler
+void __visible __aligned(16) // aligning helps stabilize perf benchmarks
+TC0_Handler(void)
+{
+    irq_disable();
+    uint32_t next = timer_dispatch_many();
+    timer_set(next);
+    irq_enable();
+}