circuitpython/ports/stm32/pendsv.c

/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2013, 2014 Damien P. George
 *
 * 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 <stdlib.h>

#include "py/runtime.h"
#include "lib/utils/interrupt_char.h"
#include "pendsv.h"
#include "irq.h"

// This variable is used to save the exception object between a ctrl-C and the
// PENDSV call that actually raises the exception.  It must be non-static
// otherwise gcc-5 optimises it away.  It can point to the heap but is not
// traced by GC.  This is okay because we only ever set it to
// mp_kbd_exception which is in the root-pointer set.
void *pendsv_object;

void pendsv_init(void) {
    // set PendSV interrupt at lowest priority
    NVIC_SetPriority(PendSV_IRQn, IRQ_PRI_PENDSV);
}

// Call this function to raise a pending exception during an interrupt.
// It will first try to raise the exception "softly" by setting the
// mp_pending_exception variable and hoping that the VM will notice it.
// If this function is called a second time (ie with the mp_pending_exception
// variable already set) then it will force the exception by using the hardware
// PENDSV feature.  This will wait until all interrupts are finished then raise
// the given exception object using nlr_jump in the context of the top-level
// thread.
void pendsv_kbd_intr(void) {
    if (MP_STATE_VM(mp_pending_exception) == MP_OBJ_NULL) {
        mp_keyboard_interrupt();
    } else {
        MP_STATE_VM(mp_pending_exception) = MP_OBJ_NULL;
        pendsv_object = &MP_STATE_VM(mp_kbd_exception);
        SCB->ICSR = SCB_ICSR_PENDSVSET_Msk;
    }
}

__attribute__((naked)) void PendSV_Handler(void) {
    // Handle a PendSV interrupt
    //
    // For the case of an asynchronous exception, re-jig the
    // stack so that when we return from this interrupt handler
    // it returns instead to nlr_jump with argument pendsv_object
    // note that stack has a different layout if DEBUG is enabled
    //
    // For the case of a thread switch, swap stacks.
    //
    // on entry to this (naked) function, stack has the following layout:
    //
    // stack layout with DEBUG disabled:
    //   sp[6]: pc=r15
    //   sp[5]: lr=r14
    //   sp[4]: r12
    //   sp[3]: r3
    //   sp[2]: r2
    //   sp[1]: r1
    //   sp[0]: r0
    //
    // stack layout with DEBUG enabled:
    //   sp[8]: pc=r15
    //   sp[7]: lr=r14
    //   sp[6]: r12
    //   sp[5]: r3
    //   sp[4]: r2
    //   sp[3]: r1
    //   sp[2]: r0
    //   sp[1]: 0xfffffff9
    //   sp[0]: ?

    __asm volatile (
        // Check if there is an active object to throw via nlr_jump
        "ldr r1, pendsv_object_ptr\n"
        "ldr r0, [r1]\n"
        "cmp r0, 0\n"
        "beq .no_obj\n"
        #if defined(PENDSV_DEBUG)
        "str r0, [sp, #8]\n"            // store to r0 on stack
        #else
        "str r0, [sp, #0]\n"            // store to r0 on stack
        #endif
        "mov r0, #0\n"
        "str r0, [r1]\n"                // clear pendsv_object
        "ldr r0, nlr_jump_ptr\n"
        #if defined(PENDSV_DEBUG)
        "str r0, [sp, #32]\n"           // store to pc on stack
        #else
        "str r0, [sp, #24]\n"           // store to pc on stack
        #endif
        "bx lr\n"                       // return from interrupt; will return to nlr_jump
        ".no_obj:\n"                    // pendsv_object==NULL

        #if MICROPY_PY_THREAD
        // Do a thread context switch
        "push {r4-r11, lr}\n"
        "vpush {s16-s31}\n"
        "mrs r5, primask\n"             // save PRIMASK in r5
        "cpsid i\n"                     // disable interrupts while we change stacks
        "mov r0, sp\n"                  // pass sp to save
        "mov r4, lr\n"                  // save lr because we are making a call
        "bl pyb_thread_next\n"          // get next thread to execute
        "mov lr, r4\n"                  // restore lr
        "mov sp, r0\n"                  // switch stacks
        "msr primask, r5\n"             // reenable interrupts
        "vpop {s16-s31}\n"
        "pop {r4-r11, lr}\n"
        "bx lr\n"                       // return from interrupt; will return to new thread
        #else
        // Spurious pendsv, just return
        "bx lr\n"
        #endif

        // Data
        ".align 2\n"
        "pendsv_object_ptr: .word pendsv_object\n"
        "nlr_jump_ptr: .word nlr_jump\n"
    );
}