Diff: hal/mbed_ticker_api.c

Revision:

0:083111ae2a11

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hal/mbed_ticker_api.c	Thu Nov 26 04:08:56 2020 +0000
@@ -0,0 +1,284 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2015 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include <stdio.h>
+#include <stddef.h>
+#include "hal/ticker_api.h"
+#include "platform/mbed_critical.h"
+
+static void schedule_interrupt(const ticker_data_t *const ticker);
+static void update_present_time(const ticker_data_t *const ticker);
+
+/*
+ * Initialize a ticker instance.  
+ */
+static void initialize(const ticker_data_t *ticker)
+{
+    // return if the queue has already been initialized, in that case the 
+    // interface used by the queue is already initialized.
+    if (ticker->queue->initialized) { 
+        return;
+    }
+
+    ticker->interface->init();
+    
+    ticker->queue->event_handler = NULL;
+    ticker->queue->head = NULL;
+    ticker->queue->present_time = 0;
+    ticker->queue->initialized = true;
+    
+    update_present_time(ticker);
+    schedule_interrupt(ticker);
+}
+
+/**
+ * Set the event handler function of a ticker instance. 
+ */
+static void set_handler(const ticker_data_t *const ticker, ticker_event_handler handler)
+{
+    ticker->queue->event_handler = handler;
+}
+
+/*
+ * Convert a 32 bit timestamp into a 64 bit timestamp.
+ *
+ * A 64 bit timestamp is used as the point of time of reference while the 
+ * timestamp to convert is relative to this point of time. 
+ *
+ * The lower 32 bits of the timestamp returned will be equal to the timestamp to 
+ * convert. 
+ * 
+ * If the timestamp to convert is less than the lower 32 bits of the time 
+ * reference then the timestamp to convert is seen as an overflowed value and 
+ * the upper 32 bit of the timestamp returned will be equal to the upper 32 bit 
+ * of the reference point + 1. 
+ * Otherwise, the upper 32 bit returned will be equal to the upper 32 bit of the 
+ * reference point. 
+ *
+ * @param ref: The 64 bit timestamp of reference.
+ * @param timestamp: The timestamp to convert.
+ */
+static us_timestamp_t convert_timestamp(us_timestamp_t ref, timestamp_t timestamp)
+{
+    bool overflow = timestamp < ((timestamp_t) ref) ? true : false;
+
+    us_timestamp_t result = (ref & ~((us_timestamp_t)UINT32_MAX)) | timestamp;
+    if (overflow) { 
+        result += (1ULL<<32);
+    }
+
+    return result;
+}
+
+/**
+ * Update the present timestamp value of a ticker.
+ */
+static void update_present_time(const ticker_data_t *const ticker)
+{ 
+    ticker->queue->present_time = convert_timestamp(
+        ticker->queue->present_time, 
+        ticker->interface->read()
+    );
+}
+
+/**
+ * Compute the time when the interrupt has to be triggered and schedule it.  
+ * 
+ * If there is no event in the queue or the next event to execute is in more 
+ * than MBED_TICKER_INTERRUPT_TIMESTAMP_MAX_DELTA us from now then the ticker 
+ * irq will be scheduled in MBED_TICKER_INTERRUPT_TIMESTAMP_MAX_DELTA us.
+ * Otherwise the irq will be scheduled to happen when the running counter reach 
+ * the timestamp of the first event in the queue.
+ * 
+ * @note If there is no event in the queue then the interrupt is scheduled to 
+ * in MBED_TICKER_INTERRUPT_TIMESTAMP_MAX_DELTA. This is necessary to keep track 
+ * of the timer overflow.
+ */
+static void schedule_interrupt(const ticker_data_t *const ticker)
+{
+    update_present_time(ticker);
+    uint32_t relative_timeout = MBED_TICKER_INTERRUPT_TIMESTAMP_MAX_DELTA;
+
+    if (ticker->queue->head) {
+        us_timestamp_t present = ticker->queue->present_time;
+        us_timestamp_t next_event_timestamp = ticker->queue->head->timestamp;
+
+        // if the event at the head of the queue is in the past then schedule
+        // it immediately.
+        if (next_event_timestamp <= present) {
+            ticker->interface->fire_interrupt();
+            return;
+        } else if ((next_event_timestamp - present) < MBED_TICKER_INTERRUPT_TIMESTAMP_MAX_DELTA) {
+            relative_timeout = next_event_timestamp - present;
+        }
+    } 
+
+    us_timestamp_t new_match_time = ticker->queue->present_time + relative_timeout;
+    ticker->interface->set_interrupt(new_match_time);
+    // there could be a delay, reread the time, check if it was set in the past
+    // As result, if it is already in the past, we fire it immediately
+    update_present_time(ticker);
+    us_timestamp_t present = ticker->queue->present_time;
+    if (present >= new_match_time) {
+        ticker->interface->fire_interrupt();
+    }
+}
+
+void ticker_set_handler(const ticker_data_t *const ticker, ticker_event_handler handler)
+{
+    initialize(ticker);
+    set_handler(ticker, handler);
+}
+
+void ticker_irq_handler(const ticker_data_t *const ticker)
+{
+    ticker->interface->clear_interrupt();
+
+    /* Go through all the pending TimerEvents */
+    while (1) {
+        if (ticker->queue->head == NULL) {
+            break;
+        }
+
+        // update the current timestamp used by the queue 
+        update_present_time(ticker);
+
+        if (ticker->queue->head->timestamp <= ticker->queue->present_time) { 
+            // This event was in the past:
+            //      point to the following one and execute its handler
+            ticker_event_t *p = ticker->queue->head;
+            ticker->queue->head = ticker->queue->head->next;
+            if (ticker->queue->event_handler != NULL) {
+                (*ticker->queue->event_handler)(p->id); // NOTE: the handler can set new events
+            }
+            /* Note: We continue back to examining the head because calling the
+             * event handler may have altered the chain of pending events. */
+        } else {
+            break;
+        } 
+    }
+
+    schedule_interrupt(ticker);
+}
+
+void ticker_insert_event(const ticker_data_t *const ticker, ticker_event_t *obj, timestamp_t timestamp, uint32_t id)
+{
+    core_util_critical_section_enter();
+
+    // update the current timestamp
+    update_present_time(ticker);
+    us_timestamp_t absolute_timestamp = convert_timestamp(
+        ticker->queue->present_time, 
+        timestamp
+    );
+    core_util_critical_section_exit();
+
+    // defer to ticker_insert_event_us
+    ticker_insert_event_us(
+        ticker, 
+        obj, absolute_timestamp, id
+    );
+}
+
+void ticker_insert_event_us(const ticker_data_t *const ticker, ticker_event_t *obj, us_timestamp_t timestamp, uint32_t id)
+{
+    core_util_critical_section_enter();
+
+    // update the current timestamp
+    update_present_time(ticker);
+
+    // initialise our data
+    obj->timestamp = timestamp;
+    obj->id = id;
+
+    /* Go through the list until we either reach the end, or find
+       an element this should come before (which is possibly the
+       head). */
+    ticker_event_t *prev = NULL, *p = ticker->queue->head;
+    while (p != NULL) {
+        /* check if we come before p */
+        if (timestamp < p->timestamp) {
+            break;
+        }
+        /* go to the next element */
+        prev = p;
+        p = p->next;
+    }
+    
+    /* if we're at the end p will be NULL, which is correct */
+    obj->next = p;
+
+    /* if prev is NULL we're at the head */
+    if (prev == NULL) {
+        ticker->queue->head = obj;
+    } else {
+        prev->next = obj;
+    }
+
+    schedule_interrupt(ticker);
+
+    core_util_critical_section_exit();
+}
+
+void ticker_remove_event(const ticker_data_t *const ticker, ticker_event_t *obj)
+{
+    core_util_critical_section_enter();
+
+    // remove this object from the list
+    if (ticker->queue->head == obj) {
+        // first in the list, so just drop me
+        ticker->queue->head = obj->next;
+        schedule_interrupt(ticker);
+    } else {
+        // find the object before me, then drop me
+        ticker_event_t* p = ticker->queue->head;
+        while (p != NULL) {
+            if (p->next == obj) {
+                p->next = obj->next;
+                break;
+            }
+            p = p->next;
+        }
+    }
+
+    core_util_critical_section_exit();
+}
+
+timestamp_t ticker_read(const ticker_data_t *const ticker)
+{
+    return ticker_read_us(ticker);
+}
+
+us_timestamp_t ticker_read_us(const ticker_data_t *const ticker)
+{
+    initialize(ticker);
+    update_present_time(ticker);
+    return ticker->queue->present_time;
+}
+
+int ticker_get_next_timestamp(const ticker_data_t *const data, timestamp_t *timestamp)
+{
+    int ret = 0;
+
+    /* if head is NULL, there are no pending events */
+    core_util_critical_section_enter();
+    if (data->queue->head != NULL) {
+        *timestamp = data->queue->head->timestamp;
+        ret = 1;
+    }
+    core_util_critical_section_exit();
+
+    return ret;
+}