1 files changed, 148 insertions, 0 deletions
diff --git a/circuitpython/supervisor/shared/background_callback.c b/circuitpython/supervisor/shared/background_callback.c
new file mode 100644
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+++ b/circuitpython/supervisor/shared/background_callback.c
@@ -0,0 +1,148 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2020 Jeff Epler for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <string.h>
+
+#include "py/gc.h"
+#include "py/mpconfig.h"
+#include "supervisor/background_callback.h"
+#include "supervisor/linker.h"
+#include "supervisor/port.h"
+#include "supervisor/shared/tick.h"
+#include "shared-bindings/microcontroller/__init__.h"
+
+STATIC volatile background_callback_t *volatile callback_head, *volatile callback_tail;
+
+#define CALLBACK_CRITICAL_BEGIN (common_hal_mcu_disable_interrupts())
+#define CALLBACK_CRITICAL_END (common_hal_mcu_enable_interrupts())
+
+MP_WEAK void port_wake_main_task(void) {
+}
+
+void background_callback_add_core(background_callback_t *cb) {
+    CALLBACK_CRITICAL_BEGIN;
+    if (cb->prev || callback_head == cb) {
+        CALLBACK_CRITICAL_END;
+        return;
+    }
+    cb->next = 0;
+    cb->prev = (background_callback_t *)callback_tail;
+    if (callback_tail) {
+        callback_tail->next = cb;
+    }
+    if (!callback_head) {
+        callback_head = cb;
+    }
+    callback_tail = cb;
+    CALLBACK_CRITICAL_END;
+
+    port_wake_main_task();
+}
+
+void background_callback_add(background_callback_t *cb, background_callback_fun fun, void *data) {
+    cb->fun = fun;
+    cb->data = data;
+    background_callback_add_core(cb);
+}
+
+bool PLACE_IN_ITCM(background_callback_pending)(void) {
+    return callback_head != NULL;
+}
+
+static bool in_background_callback;
+void PLACE_IN_ITCM(background_callback_run_all)() {
+    if (!background_callback_pending()) {
+        return;
+    }
+    CALLBACK_CRITICAL_BEGIN;
+    if (in_background_callback) {
+        CALLBACK_CRITICAL_END;
+        return;
+    }
+    in_background_callback = true;
+    background_callback_t *cb = (background_callback_t *)callback_head;
+    callback_head = NULL;
+    callback_tail = NULL;
+    while (cb) {
+        background_callback_t *next = cb->next;
+        cb->next = cb->prev = NULL;
+        background_callback_fun fun = cb->fun;
+        void *data = cb->data;
+        CALLBACK_CRITICAL_END;
+        // Leave the critical section in order to run the callback function
+        if (fun) {
+            fun(data);
+        }
+        CALLBACK_CRITICAL_BEGIN;
+        cb = next;
+    }
+    in_background_callback = false;
+    CALLBACK_CRITICAL_END;
+}
+
+void background_callback_begin_critical_section() {
+    CALLBACK_CRITICAL_BEGIN;
+}
+
+void background_callback_end_critical_section() {
+    CALLBACK_CRITICAL_END;
+}
+
+void background_callback_reset() {
+    CALLBACK_CRITICAL_BEGIN;
+    background_callback_t *cb = (background_callback_t *)callback_head;
+    while (cb) {
+        background_callback_t *next = cb->next;
+        memset(cb, 0, sizeof(*cb));
+        cb = next;
+    }
+    callback_head = NULL;
+    callback_tail = NULL;
+    in_background_callback = false;
+    CALLBACK_CRITICAL_END;
+}
+
+void background_callback_gc_collect(void) {
+    // We don't enter the callback critical section here.  We rely on
+    // gc_collect_ptr _NOT_ entering background callbacks, so it is not
+    // possible for the list to be cleared.
+    //
+    // However, it is possible for the list to be extended.  We make the
+    // minor assumption that no newly added callback is for a
+    // collectable object.  That is, we only plug the hole where an
+    // object becomes collectable AFTER it is added but before the
+    // callback is run, not the hole where an object was ALREADY
+    // collectable but adds a background task for itself.
+    //
+    // It's necessary to traverse the whole list here, as the callbacks
+    // themselves can be in non-gc memory, and some of the cb->data
+    // objects themselves might be in non-gc memory.
+    background_callback_t *cb = (background_callback_t *)callback_head;
+    while (cb) {
+        gc_collect_ptr(cb->data);
+        cb = cb->next;
+    }
+}