sam3: Rename src/sam3x8e to src/sam3

This is in preparation for merging sam3 and sam4 code into one
directory.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/sam3/timer.c

@@ -0,0 +1,65 @@
+// SAM3x8e timer interrupt scheduling
+//
+// Copyright (C) 2016,2017  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 "command.h" // DECL_SHUTDOWN
+#include "sam3x8e.h" // TC0
+#include "sched.h" // DECL_INIT
+
+// Set the next irq time
+static void
+timer_set(uint32_t value)
+{
+    TC0->TC_CHANNEL[0].TC_RA = value;
+}
+
+// Return the current time (in absolute clock ticks).
+uint32_t
+timer_read_time(void)
+{
+    return TC0->TC_CHANNEL[0].TC_CV;
+}
+
+// Activate timer dispatch as soon as possible
+void
+timer_kick(void)
+{
+    timer_set(timer_read_time() + 50);
+    TC0->TC_CHANNEL[0].TC_SR; // read to clear irq pending
+}
+
+void
+timer_init(void)
+{
+    TcChannel *tc = &TC0->TC_CHANNEL[0];
+    // Reset the timer
+    tc->TC_CCR = TC_CCR_CLKDIS;
+    tc->TC_IDR = 0xFFFFFFFF;
+    // Enable it
+    PMC->PMC_PCER0 = 1 << ID_TC0;
+    tc->TC_CMR = TC_CMR_WAVE | TC_CMR_WAVSEL_UP | TC_CMR_TCCLKS_TIMER_CLOCK1;
+    tc->TC_IER = TC_IER_CPAS;
+    NVIC_SetPriority(TC0_IRQn, 1);
+    NVIC_EnableIRQ(TC0_IRQn);
+    timer_kick();
+    tc->TC_CCR = TC_CCR_CLKEN | TC_CCR_SWTRG;
+}
+DECL_INIT(timer_init);
+
+// IRQ handler
+void __visible __aligned(16) // aligning helps stabilize perf benchmarks
+TC0_Handler(void)
+{
+    irq_disable();
+    uint32_t status = TC0->TC_CHANNEL[0].TC_SR; // read to clear irq pending
+    if (likely(status & TC_SR_CPAS)) {
+        uint32_t next = timer_dispatch_many();
+        timer_set(next);
+    }
+    irq_enable();
+}