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/main.c

@@ -0,0 +1,48 @@
+// SAM4e8e port main entry
+//
+// 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 "command.h" // DECL_CONSTANT
+#include "sched.h" // sched_main
+
+DECL_CONSTANT(MCU, "sam4e8e");
+
+#define WDT_PASSWORD 0xA5000000
+#define WDT_SLOW_CLOCK_DIV 128
+
+void
+watchdog_reset(void)
+{
+    WDT->WDT_CR = WDT_PASSWORD | WDT_CR_WDRSTT;
+}
+DECL_TASK(watchdog_reset);
+
+void
+watchdog_init(void)
+{
+    uint32_t timeout = 500000 / (WDT_SLOW_CLOCK_DIV * 1000000 / 32768UL);
+    WDT->WDT_MR = WDT_MR_WDRSTEN | WDT_MR_WDV(timeout) | WDT_MR_WDD(timeout);
+}
+DECL_INIT(watchdog_init);
+
+void
+command_reset(uint32_t *args)
+{
+    NVIC_SystemReset();
+}
+DECL_COMMAND_FLAGS(command_reset, HF_IN_SHUTDOWN, "reset");
+
+// Main entry point
+int
+main(void)
+{
+    SystemInit();
+    sched_main();
+    return 0;
+}