Initial add of i2s_loopback test

tests/i2s_loopback/xk_216_mc/gpio_access.c

@@ -0,0 +1,41 @@
+// Copyright (c) 2016, XMOS Ltd, All rights reserved
+#ifdef HARDWARE
+#include <xs1.h>
+#include "gpio_access.h"
+
+void p_gpio_lock()
+{
+}
+
+void p_gpio_unlock()
+{
+}
+
+unsigned p_gpio_peek()
+{
+    unsigned portId, x;
+
+    asm("ldw %0, dp[p_gpio]":"=r"(portId));
+    asm volatile("peek %0, res[%1]":"=r"(x):"r"(portId));
+
+    return x;
+}
+
+void p_gpio_out(unsigned x)
+{
+    unsigned portId;
+
+    asm("ldw %0, dp[p_gpio]":"=r"(portId));
+    asm volatile("out res[%0], %1"::"r"(portId),"r"(x));
+}
+
+void set_gpio(unsigned bit, unsigned value)
+{
+	unsigned port_shadow;
+	port_shadow = p_gpio_peek();         // Read port pin value
+	if (value == 0) port_shadow &= ~bit; // If writing a 0, generate mask and AND with current val
+	else port_shadow |= bit;             // Else use mask and OR to set bit
+	p_gpio_out(port_shadow);             // Write back to port. Will make port an output if not already
+}
+
+#endif