Adding implementation for us_ticker APIs. Not complete, yet to be tested.

libraries/mbed/targets/hal/TARGET_Atmel/TARGET_SAM21/us_ticker.c

@@ -19,29 +19,95 @@
 #include "mbed_assert.h"
 #include "ins_gclk.h"
 #include "compiler.h"
+#include "tc.h"
+#include "tc_interrupt.h"
 
-void us_ticker_irq_handler_internal(void)
+static int us_ticker_inited = 0;
+
+struct tc_module us_ticker_module;
+
+void us_ticker_irq_handler_internal(struct tc_module* us_tc_module)
 {
-    
+	us_ticker_irq_handler();
+	
+	/* Disable the callback */
+	tc_disable_callback(us_tc_module, TC_CALLBACK_CC_CHANNEL0);
 }
 
 void us_ticker_init(void)
 {
+	uint32_t			cycles_per_us;
+	uint32_t			prescaler = 0;
+	struct tc_config	config_tc;
+	enum status_code	ret_status;
+	
+	if (us_ticker_inited) return;
+	us_ticker_inited = 1;
 
+
+	tc_get_config_defaults(&config_tc);
+	
+	cycles_per_us = system_gclk_gen_get_hz(config_tc.clock_source) / 1000000;
+	MBED_ASSERT(cycles_per_us > 0);
+	while((cycles_per_us & 1) == 0 && prescaler <= 10) {
+		cycles_per_us = cycles_per_us >> 1;
+		prescaler++;
+	}
+	config_tc.clock_prescaler = TC_CTRLA_PRESCALER(prescaler);
+	config_tc.counter_size = TC_COUNTER_SIZE_32BIT;
+	config_tc.counter_32_bit.value = 0;
+	config_tc.counter_32_bit.compare_capture_channel[0] = 0xFFFFFFFF;
+	
+	//config_tc.oneshot = true;
+
+	/* Initialize the timer */
+	ret_status = tc_init(&us_ticker_module, TC4, &config_tc);
+	MBED_ASSERT(ret_status == STATUS_OK);
+	
+	/* Register callback function */
+	tc_register_callback(&us_ticker_module, (tc_callback_t)us_ticker_irq_handler_internal, TC_CALLBACK_CC_CHANNEL0);
+	
+	/* Enable the timer module */
+	tc_enable(&us_ticker_module);
 }
 
 uint32_t us_ticker_read()
 {
-
+	if (!us_ticker_inited)
+        us_ticker_init();
+	
+	return tc_get_count_value(&us_ticker_module);
 }
 
 void us_ticker_set_interrupt(timestamp_t timestamp)
 {
-    
+	uint32_t cur_time;
+	int32_t delta;
+	
+	cur_time = us_ticker_read();
+	delta = (int32_t)((uint32_t)timestamp - cur_time);
+	if (delta < 0)
+	{
+		/* Event already occurred in past */
+		us_ticker_irq_handler();
+		return;
+	}
+	
+	tc_set_compare_value(&us_ticker_module, TC_CALLBACK_CC_CHANNEL0, timestamp);
+	
+	/* Enable the callback */
+	tc_enable_callback(&us_ticker_module, TC_CALLBACK_CC_CHANNEL0);
+	
+	/* Enable the timer module */
+	//tc_enable(&us_ticker_module);
 }
 
-void us_ticker_clear_interrupt(void)
-{
-    
+void us_ticker_disable_interrupt(void) {
+	/* Disable the callback */
+	tc_disable_callback(&us_ticker_module, TC_CALLBACK_CC_CHANNEL0);
 }
-/***************************************************************/
+
+void us_ticker_clear_interrupt(void) {
+	/* Disable the callback */
+	tc_disable_callback(&us_ticker_module, TC_CALLBACK_CC_CHANNEL0);
+}