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/**
* @file task.c
* Provides multitasking functionality
*
* Copyright (C) 2018 Clyne Sullivan
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include <task.h>
#include <heap.h>
#include <stm32l476xx.h>
task_t *current, *prev;
static uint8_t task_disable = 0;
void task_hold(uint8_t hold)
{
if (hold != 0)
task_disable++;
else if (task_disable > 0)
task_disable--;
}
void _exit(int code)
{
(void)code;
while (prev == 0);
prev->next = current->next;
// Free this thread's stack, and task data.
// Since we're single core, no one else can claim this memory until
// a task switch, after which we're done with this memory anyway.
free(current->stack);
free(current);
SCB->ICSR |= SCB_ICSR_PENDSVSET_Msk;
while (1);
}
/**
* 'Prepares' task for running.
* Calls the task's main code, setting _exit() as the return point.
*/
__attribute__ ((naked))
void task_crt0(void)
{
asm("\
mov r4, lr; \
ldr lr, =_exit; \
bx r4; \
");
}
task_t *task_create(void (*code)(void), uint32_t stackSize)
{
task_t *t = (task_t *)malloc(sizeof(task_t));
t->next = 0;
t->stack = (uint32_t *)malloc(stackSize);
void *sp = (uint8_t *)t->stack + stackSize - 68; // excep. stack + regs
t->sp = sp;
/*
sp[0-7] - r4-r11
sp[8] - r14 (lr)
sp[9-12] - r0-r3
sp[13] - r12
sp[14] - LR
sp[15] - PC
sp[16] - xPSR
*/
for (uint8_t i = 0; i < 14; i++)
t->sp[i] = 0;
t->sp[8] = 0xFFFFFFFD;
t->sp[14] = (uint32_t)code;
t->sp[15] = (uint32_t)task_crt0;
t->sp[16] = 0x01000000;
return t;
}
void task_init(void (*init)(void))
{
current = (task_t *)malloc(sizeof(task_t));
task_t *init_task = task_create(init, 4096);
current->next = init_task;
init_task->next = init_task;
task_disable = 0;
// bit 0 - priv, bit 1 - psp/msp
asm("\
mov r0, sp; \
mov %0, r0; \
msr psp, r0; \
mrs r0, control; \
orr r0, r0, #2; \
cpsie i; \
msr control, r0; \
" : "=r" (current->sp));
SCB->ICSR |= SCB_ICSR_PENDSVSET_Msk;
while (1);
}
void task_start(void (*task)(void), uint16_t stackSize)
{
task_hold(1);
task_t *t = task_create(task, stackSize);
t->next = current->next;
current->next = t;
task_hold(0);
}
/*int fork_ret(void)
{
return 1;
}
int fork(void)
{
void (*pc)(void) = (void (*)(void))((uint32_t)fork_ret & ~(3));
task_hold(1);
// duplicate task info
alloc_t *heapInfo = (alloc_t *)(current->stack - 2);
task_t *t = task_create(pc, heapInfo->size);
memcpy(t->stack, current->stack, heapInfo->size);
uint32_t *sp;
asm("mov %0, sp" : "=r" (sp));
t->sp = t->stack + (sp - current->stack);
t->next = current->next;
current->next = t;
current = t;
task_hold(0);
SCB->ICSR |= SCB_ICSR_PENDSVSET_Msk;
return 0;
}*/
__attribute__ ((naked))
void PendSV_Handler(void)
{
if (task_disable != 0)
asm("bx lr");
// TODO why, and what does this do
asm("\
mrs r0, psp; \
isb; \
ldr r1, =current; \
ldr r2, [r1]; \
stmdb r0!, {r4-r11, r14}; \
str r0, [r2, #8]; \
ldr r0, [r2, #0]; \
ldr r3, =prev; \
str r2, [r3]; \
str r0, [r1]; \
ldr r2, [r1]; \
ldr r0, [r2, #8]; \
ldmia r0!, {r4-r11, r14}; \
msr psp, r0; \
bx lr; \
");
// r1 = current
// r2 = *current
// r0 = sp
// *current.sp = sp
// r0 = current->next
// current = r0
// r2 = *current
// r0 = *current.sp
// unpack
}
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