eced9d86a7
Fixes a regression introduced in 3af006efb39ad0b7aa7c0401c93329b654bca617 where WFE never blocked in `mp_wfe_or_timeout()` function and would busy-wait instead. This increases power consumption measurably. Root cause is that `mp_wfe_or_timeout()` calls soft timer functions that (after the regression) call `recursive_mutex_enter()` and `recursive_mutex_exit()`. The exit calls `lock_internal_spin_unlock_with_notify()` and the default pico-sdk implementation of this macro issues a SEV which negates the WFE that follows it, meaning the CPU never suspends. See https://forums.raspberrypi.com/viewtopic.php?p=2233908 for more details. The fix in this comment adds a custom "nowait" variant mutex that doesn't do WFE/SEV, and uses this one for PendSV. This will use more power when there's contention for the PendSV mutex as the other core will spin, but this shouldn't happen very often. This work was funded through GitHub Sponsors. Signed-off-by: Angus Gratton <angus@redyak.com.au>
107 lines
3.7 KiB
C
107 lines
3.7 KiB
C
/*
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* This file is part of the MicroPython project, http://micropython.org/
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*
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* The MIT License (MIT)
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*
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* Copyright (c) 2022 Damien P. George
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#include <assert.h>
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#include "py/mpconfig.h"
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#include "mutex_extra.h"
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#include "pendsv.h"
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#include "RP2040.h"
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#if MICROPY_PY_NETWORK_CYW43
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#include "lib/cyw43-driver/src/cyw43_stats.h"
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#endif
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static pendsv_dispatch_t pendsv_dispatch_table[PENDSV_DISPATCH_NUM_SLOTS];
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// Using the nowait variant here as softtimer updates PendSV from the loop of mp_wfe_or_timeout(),
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// where we don't want the CPU event bit to be set.
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static recursive_mutex_nowait_t pendsv_mutex;
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void pendsv_init(void) {
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recursive_mutex_nowait_init(&pendsv_mutex);
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}
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void pendsv_suspend(void) {
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// Recursive Mutex here as either core may call pendsv_suspend() and expect
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// both mutual exclusion (other core can't enter pendsv_suspend() at the
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// same time), and that no PendSV handler will run.
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recursive_mutex_nowait_enter_blocking(&pendsv_mutex);
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}
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void pendsv_resume(void) {
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recursive_mutex_nowait_exit(&pendsv_mutex);
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// Run pendsv if needed. Find an entry with a dispatch and call pendsv dispatch
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// with it. If pendsv runs it will service all slots.
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int count = PENDSV_DISPATCH_NUM_SLOTS;
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while (count--) {
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if (pendsv_dispatch_table[count]) {
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pendsv_schedule_dispatch(count, pendsv_dispatch_table[count]);
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break;
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}
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}
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}
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void pendsv_schedule_dispatch(size_t slot, pendsv_dispatch_t f) {
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pendsv_dispatch_table[slot] = f;
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if (pendsv_mutex.mutex.enter_count == 0) {
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// There is a race here where other core calls pendsv_suspend() before
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// ISR can execute, but dispatch will happen later when other core
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// calls pendsv_resume().
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SCB->ICSR = SCB_ICSR_PENDSVSET_Msk;
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} else {
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#if MICROPY_PY_NETWORK_CYW43
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CYW43_STAT_INC(PENDSV_DISABLED_COUNT);
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#endif
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}
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}
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// PendSV interrupt handler to perform background processing.
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void PendSV_Handler(void) {
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if (!recursive_mutex_nowait_try_enter(&pendsv_mutex, NULL)) {
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// Failure here means core 1 holds pendsv_mutex. ISR will
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// run again after core 1 calls pendsv_resume().
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return;
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}
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// Core 0 should not already have locked pendsv_mutex
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assert(pendsv_mutex.mutex.enter_count == 1);
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#if MICROPY_PY_NETWORK_CYW43
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CYW43_STAT_INC(PENDSV_RUN_COUNT);
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#endif
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for (size_t i = 0; i < PENDSV_DISPATCH_NUM_SLOTS; ++i) {
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if (pendsv_dispatch_table[i] != NULL) {
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pendsv_dispatch_t f = pendsv_dispatch_table[i];
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pendsv_dispatch_table[i] = NULL;
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f();
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}
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}
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recursive_mutex_nowait_exit(&pendsv_mutex);
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}
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