us_ticker_api.c

00001 /* mbed Microcontroller Library
00002  * Copyright (c) 2006-2013 ARM Limited
00003  *
00004  * Licensed under the Apache License, Version 2.0 (the "License");
00005  * you may not use this file except in compliance with the License.
00006  * You may obtain a copy of the License at
00007  *
00008  *     http://www.apache.org/licenses/LICENSE-2.0
00009  *
00010  * Unless required by applicable law or agreed to in writing, software
00011  * distributed under the License is distributed on an "AS IS" BASIS,
00012  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00013  * See the License for the specific language governing permissions and
00014  * limitations under the License.
00015  */
00016 #include <stddef.h>
00017 #include "us_ticker_api.h"
00018 #include "cmsis.h"
00019 
00020 static ticker_event_handler event_handler;
00021 static ticker_event_t *head = NULL;
00022 
00023 void us_ticker_set_handler(ticker_event_handler handler) {
00024     us_ticker_init();
00025 
00026     event_handler = handler;
00027 }
00028 
00029 void us_ticker_irq_handler(void) {
00030     us_ticker_clear_interrupt();
00031 
00032     /* Go through all the pending TimerEvents */
00033     while (1) {
00034         if (head == NULL) {
00035             // There are no more TimerEvents left, so disable matches.
00036             us_ticker_disable_interrupt();
00037             return;
00038         }
00039 
00040         if ((int)(head->timestamp - us_ticker_read()) <= 0) {
00041             // This event was in the past:
00042             //      point to the following one and execute its handler
00043             ticker_event_t *p = head;
00044             head = head->next;
00045             if (event_handler != NULL) {
00046                 event_handler(p->id); // NOTE: the handler can set new events
00047             }
00048             /* Note: We continue back to examining the head because calling the
00049              * event handler may have altered the chain of pending events. */
00050         } else {
00051             // This event and the following ones in the list are in the future:
00052             //      set it as next interrupt and return
00053             us_ticker_set_interrupt(head->timestamp);
00054             return;
00055         }
00056     }
00057 }
00058 
00059 void us_ticker_insert_event(ticker_event_t *obj, timestamp_t timestamp, uint32_t id) {
00060     /* disable interrupts for the duration of the function */
00061     __disable_irq();
00062 
00063     // initialise our data
00064     obj->timestamp = timestamp;
00065     obj->id = id;
00066 
00067     /* Go through the list until we either reach the end, or find
00068        an element this should come before (which is possibly the
00069        head). */
00070     ticker_event_t *prev = NULL, *p = head;
00071     while (p != NULL) {
00072         /* check if we come before p */
00073         if ((int)(timestamp - p->timestamp) < 0) {
00074             break;
00075         }
00076         /* go to the next element */
00077         prev = p;
00078         p = p->next;
00079     }
00080 
00081     /* if we're at the end p will be NULL, which is correct */
00082     obj->next = p;
00083 
00084     /* if prev is NULL we're at the head */
00085     if (prev == NULL) {
00086         head = obj;
00087         us_ticker_set_interrupt(timestamp);
00088     } else {
00089         prev->next = obj;
00090     }
00091 
00092     __enable_irq();
00093 }
00094 
00095 void us_ticker_remove_event(ticker_event_t *obj) {
00096     __disable_irq();
00097 
00098     // remove this object from the list
00099     if (head == obj) {
00100         // first in the list, so just drop me
00101         head = obj->next;
00102         if (head == NULL) {
00103             us_ticker_disable_interrupt();
00104         } else {
00105             us_ticker_set_interrupt(head->timestamp);
00106         }
00107     } else {
00108         // find the object before me, then drop me
00109         ticker_event_t* p = head;
00110         while (p != NULL) {
00111             if (p->next == obj) {
00112                 p->next = obj->next;
00113                 break;
00114             }
00115             p = p->next;
00116         }
00117     }
00118 
00119     __enable_irq();
00120 }
00121 
00122 int us_ticker_get_next_timestamp(timestamp_t *timestamp) {
00123     int ret = 0;
00124 
00125     /* if head is NULL, there are no pending events */
00126     __disable_irq();
00127     if (head != NULL) {
00128         *timestamp = head->timestamp;
00129         ret = 1;
00130     }
00131     __enable_irq();
00132 
00133     return ret;
00134 }