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/* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*
* Context swtching
*/
#include "config.h"
.text
.syntax unified
.code 16
/**
* Task context switching
*
* Change the task scheduled after returning from the exception.
*
* Save the registers of the current task below the exception context on
* its task, then restore the live registers of the next task and set the
* process stack pointer to the new stack.
*
* r0: pointer to the task to switch from
* r1: pointer to the task to switch to
*
* must be called from interrupt context
*
* the structure of the saved context on the stack is :
* r0, r1, r2, r3, r12, lr, pc, psr, r4, r5, r6, r7, r8, r9, r10, r11
* exception frame <|> additional registers
*/
.global __switchto
.thumb_func
__switchto:
mrs r3, psp @ get the task stack where the context has been saved
ldr r2, [r1] @ get the new scheduled task stack pointer
stmdb r3!, {r4-r11} @ save additional r4-r7 in the task stack
ldmia r2!, {r4-r11} @ restore r4-r7 for the next task context
str r3, [r0] @ save the task stack pointer in its context
msr psp, r2 @ set the process stack pointer to exception context
bx lr @ return from exception
/**
* Start the task scheduling. r0 is a pointer to task_stack_ready, which is
* set to 1 after the task stack is set up.
*/
.global __task_start
.thumb_func
__task_start:
ldr r2,=scratchpad @ area used as dummy thread stack for the first switch
mov r3, #2
add r2, #17*4 @ put the pointer at the top of the stack
mov r1, #0 @ __Schedule parameter : re-schedule nothing
msr psp, r2 @ setup a thread stack up to the first context switch
mov r2, #1
isb @ ensure the write is done
msr control, r3 @ use : priv. mode / thread stack / no floating point
mov r3, r0
mov r0, #0 @ __Schedule parameter : de-schedule nothing
isb @ ensure the write is done
str r2, [r3] @ Task scheduling is now active
bl __schedule @ execute the task with the highest priority
/* we should never return here */
mov r0, #1 @ set to EC_ERROR_UNKNOWN
bx lr
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