sam4e8e: Add the SAM4e8e port

This can be flashed to e.g. the duet wifi using bossac. It requires a
later version as is currently included in the klipper repo (1.8
vs. 1.2). Comms are currently via UART0 only, USB serial is still TBD

Signed-off-by: Florian Heilmann <Florian.Heilmann@gmx.net>

src/sam4e8e/timer.c

@@ -0,0 +1,67 @@
+// SAM4e8e timer port
+//
+// Copyright (C) 2018  Florian Heilmann <Florian.Heilmann@gmx.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+// CMSIS
+#include "sam.h"
+// Klipper
+#include "board/irq.h" // irq_disable
+#include "board/misc.h" // timer_read_time
+#include "board/timer_irq.h" // timer_dispatch_many
+#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;
+}
+
+void
+timer_init(void)
+{
+    if ((PMC->PMC_PCSR0 & (1u << ID_TC0)) == 0) {
+        PMC->PMC_PCER0 = 1 << ID_TC0;
+    }
+    TcChannel *tc_channel = &TC0->TC_CHANNEL[0];
+    tc_channel->TC_CCR = TC_CCR_CLKDIS;
+    tc_channel->TC_IDR = 0xFFFFFFFF;
+    tc_channel->TC_SR;
+    tc_channel->TC_CMR = TC_CMR_WAVE | TC_CMR_WAVSEL_UP | TC_CMR_TCCLKS_TIMER_CLOCK1;
+    tc_channel->TC_IER = TC_IER_CPAS;
+    NVIC_SetPriority(TC0_IRQn, 1);
+    NVIC_EnableIRQ(TC0_IRQn);
+    timer_kick();
+    tc_channel->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;
+    if (likely(status & TC_SR_CPAS)) {
+        uint32_t next = timer_dispatch_many();
+        timer_set(next);
+    }
+    irq_enable();
+}