Rework us_ticker.c, work-around for #8656

Author: janjongboom

targets/TARGET_Atmel/TARGET_SAM_CortexM0P/us_ticker.c

@@ -85,10 +85,7 @@ void us_ticker_init(void)
 
     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++;
-    }*/
+
     while((cycles_per_us > 1) && (prescaler <= 10)) {
         cycles_per_us = cycles_per_us >> 1;
         prescaler++;
@@ -115,6 +112,11 @@ void us_ticker_init(void)
 
     /* Enable the timer module */
     tc_enable(&us_ticker_module);
+
+    /* Enable the timer interrupt */
+    tc_disable_callback(&us_ticker_module, TC_CALLBACK_CC_CHANNEL0);
+    NVIC_SetVector(TICKER_COUNTER_IRQn, (uint32_t)TICKER_COUNTER_Handlr);
+    NVIC_EnableIRQ(TICKER_COUNTER_IRQn);
 }
 
 uint32_t us_ticker_read()
@@ -127,37 +129,33 @@ uint32_t us_ticker_read()
 
 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;
-    }
-
-    NVIC_DisableIRQ(TICKER_COUNTER_IRQn);
-    NVIC_SetVector(TICKER_COUNTER_IRQn, (uint32_t)TICKER_COUNTER_Handlr);
-
     /* Enable the callback */
     tc_enable_callback(&us_ticker_module, TC_CALLBACK_CC_CHANNEL0);
     tc_set_compare_value(&us_ticker_module, TC_COMPARE_CAPTURE_CHANNEL_0, (uint32_t)timestamp);
-
-    NVIC_EnableIRQ(TICKER_COUNTER_IRQn);
 }
 
 void us_ticker_disable_interrupt(void)
 {
     /* Disable the callback */
     tc_disable_callback(&us_ticker_module, TC_CALLBACK_CC_CHANNEL0);
-    NVIC_DisableIRQ(TICKER_COUNTER_IRQn);
 }
 
 void us_ticker_fire_interrupt(void)
 {
-    NVIC_SetPendingIRQ(TICKER_COUNTER_IRQn);
+    /**
+     * We should be able to trigger this by just calling:
+     *
+     * NVIC_SetPendingIRQ(TICKER_COUNTER_IRQn);
+     *
+     * However, tc_interrupt.c -> _tc_interrupt_handler then gets the wrong value from reg.
+     * It should be 48 (when called via the normal API), but is 32. I've tried setting
+     * this register before triggering the interrupt, and this fails in the same way.
+     * I have no clue how to fix this properly... If someone comes along who understands
+     * Atmel IRQ handling better I'd love to get a better patch
+     */
+
+    // this gives us a minimum tick of 400 us.
+    us_ticker_set_interrupt(us_ticker_read() + 400);
 }
 
 void us_ticker_clear_interrupt(void)
@@ -175,5 +173,8 @@ void us_ticker_clear_interrupt(void)
 
 void us_ticker_free(void)
 {
+    tc_clear_interrupt(&us_ticker_module, TC_CALLBACK_CC_CHANNEL0);
+    NVIC_DisableIRQ(TICKER_COUNTER_IRQn);
 
+    us_ticker_inited = 0;
 }