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137 lines
3.9 KiB
C
137 lines
3.9 KiB
C
/*
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* Copyright (C) 2016 Kaspar Schleiser <kaspar@schleiser.de>
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* 2014, Freie Universitaet Berlin (FUB) & INRIA.
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* All rights reserved.
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*
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* This file is subject to the terms and conditions of the GNU Lesser
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* General Public License v2.1. See the file LICENSE in the top level
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* directory for more details.
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*/
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#include "cpu.h"
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#include "kernel_init.h"
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#include "irq.h"
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#include "sched.h"
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#include "thread.h"
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/*
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* This function can both be called from ISR and from thread context.
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*
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* In both cases, the caller will use "CALL", which pushes the return
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* address on the stack before executing the function's first instruction.
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*
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* If called within ISR, just set sched_context_switch_request and
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* directly return to the call site. A regular function return does this.
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*
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* If called from stack context, it needs to prepare the stack so it looks exactly
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* as if the thread had been interrupted by an ISR, which requires the SR to be on
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* stack right after the return address. So we do this manually.
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* __save_context() will then save the remaining registers, then store the stack
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* pointer in the thread's thread_t.
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*
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* At this point, the thread context is properly saved. sched_run (possibly) changes
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* the currently active thread, which __restore_context() then restores, resuming
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* execution at the call site using reti.
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*
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*/
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void thread_yield_higher(void)
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{
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if (irq_is_in()) {
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sched_context_switch_request = 1;
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}
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else {
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__asm__ volatile (
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"push r2" "\n\t" /* save SR */
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"dint" "\n\t" /* reti will restore SR, and thus, IRQ state */
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"nop" "\n\t" /* dint takes an additional CPU cycle to take into effect */
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: /* no outputs */
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: /* no inputs */
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: /* no clobbers */
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);
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__save_context();
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/* have thread_get_active() point to the next thread */
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sched_run();
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__restore_context();
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UNREACHABLE();
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}
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}
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/* This function calculates the ISR_usage */
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int thread_isr_stack_usage(void)
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{
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/* TODO */
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return -1;
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}
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void *thread_isr_stack_pointer(void)
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{
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/* TODO */
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return (void *)-1;
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}
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void *thread_isr_stack_start(void)
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{
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/* TODO */
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return (void *)-1;
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}
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NORETURN void cpu_switch_context_exit(void)
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{
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sched_run();
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__restore_context();
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UNREACHABLE();
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}
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/**
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* mspgcc handles main specially - it does not return but falls
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* through to section .fini9.
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* To "fix" this, we put a return in section .fini9 to make main
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* behave like a regular function. This enables a common
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* thread_stack_init behavior. */
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__attribute__((section (".fini9"))) void __main_epilogue(void) { __asm__("ret"); }
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/* ------------------------------------------------------------------------- */
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/* Processor specific routine - here for MSP */
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/* ------------------------------------------------------------------------- */
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char *thread_stack_init(thread_task_func_t task_func, void *arg, void *stack_start, int stack_size)
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{
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unsigned short stk = (unsigned short)((uintptr_t) stack_start + stack_size);
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/* ensure correct stack alignment (on 16-bit boundary) */
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stk &= 0xfffe;
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unsigned short *stackptr = (unsigned short *)stk;
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/* now make SP point on the first AVAILABLE slot in stack */
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--stackptr;
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*stackptr = (unsigned short) sched_task_exit;
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--stackptr;
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*stackptr = (unsigned short) task_func;
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--stackptr;
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/* initial value for SR */
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*stackptr = GIE;
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--stackptr;
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/* Space for registers. */
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for (unsigned int i = 15; i > 4; i--) {
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*stackptr = i;
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--stackptr;
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}
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/* set arg to R12
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this was R15 in mspgcc, see https://www.ti.com/lit/an/slaa664/slaa664.pdf
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stackptr points to R3, so write arg 9 words after that.
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*/
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stackptr[8] = (intptr_t)arg;
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return (char *) stackptr;
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}
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