ticker_api_fix.c

00001 #include <stddef.h>
00002 #include "ticker_api.h"
00003 
00004 void $Sub$$ticker_insert_event(const ticker_data_t *const data, ticker_event_t *obj, timestamp_t timestamp, uint32_t id) {
00005     /* disable interrupts for the duration of the function */
00006     __disable_irq();
00007 
00008     // initialise our data
00009     obj->timestamp = timestamp;
00010     obj->id = id;
00011 
00012     /* Go through the list until we either reach the end, or find
00013        an element this should come before (which is possibly the
00014        head). */
00015     ticker_event_t *prev = NULL, *p = data->queue->head;
00016     while (p != NULL) {
00017         /* check if we come before p */
00018         if ((int)(timestamp - p->timestamp) < 0) {
00019             break;
00020         }
00021         /* go to the next element */
00022         prev = p;
00023         p = p->next;
00024     }
00025 
00026     /* if we're at the end p will be NULL, which is correct */
00027     // BUG FIX: do this BEFORE calling set_interrupt(), to ensure
00028     // that the list is in a consistent state if set_interrupt()
00029     // happens to call the event handler, and the event handler
00030     // happens to call back here to re-queue the event.  Such
00031     // things aren't hypothetical: this exact thing will happen
00032     // if a Ticker object gets more than one cycle behind.  The
00033     // inconsistent state of the list caused crashes.
00034     obj->next = p;
00035 
00036     /* if prev is NULL we're at the head */
00037     if (prev == NULL) {
00038         data->queue->head = obj;
00039         data->interface->set_interrupt(timestamp);
00040     } else {
00041         prev->next = obj;
00042     }
00043 
00044     __enable_irq();
00045 }
00046