New Contiki port to STM32W108.
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158
cpu/stm32w108/hal/micro/cortexm3/context-switch.s79
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cpu/stm32w108/hal/micro/cortexm3/context-switch.s79
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//------------------------------------------------------------------------------
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// @file hal/micro/cortexm3/context-switch.s79
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// @brief Context save/restore for deep sleep using the PendSV exception.
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//
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// This file also contains a simple halInternalIdleSleep() function that
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// executes just the WFI instruction for idle sleeping.
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//
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// When the STM32W108XX enters deep sleep, the hardware will actually remove power
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// from the Cortex-M3 core (in Deep Sleep 0, power is not removed but the core
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// is held in reset). Since this will clear the internal state of the core, it
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// must be properly restored such that execution can resume from the sleep code.
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// The simplest and most secure mechanism to do this is to perform a context save
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// and restore. Context save/restore is almost identical to a context switch
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// used in multi-threaded systems with the main difference being only one stack
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// pointer is used and the save/restore operations are disjoint.
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//
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// When an interrupt is triggered in the STM32W108XX, the core automatically saves 8
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// of the 16 CPU registers on the stack. The ISR then only needs to save the
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// other 8 registers and store the resulting stack pointer. Restoring is the
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// reverse operation where 8 registers are manually copied back with the other 8
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// being restored on the return from interrupt.
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//
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// As its last act, the deep sleep code will trigger the PendSV exception to
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// perform a context save. When the core is booted upon deep sleep exit, the
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// RESET_EVENT register informs cstartup if the chip just exited deep sleep.
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// Cstartup will then trigger halTriggerContextRestore which sets up the stack
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// pointer and trigger the PendSV exception to perform a restore. When PendSV
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// returns from interrupt context the system will be back at the same point it
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// was before deep sleep.
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//
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//
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// <!--(C) COPYRIGHT 2010 STMicroelectronics. All rights reserved. -->
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//------------------------------------------------------------------------------
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#include "compiler/asm.h"
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//------------------------------------------------------------------------------
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// boolean halPendSvSaveContext
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//
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// A simple boolean flag used to indicate if a context save or a context restore
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// should be performed. Since context switching is handled with the PendSV
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// interrupt, parameters cannot be passed into the ISR and as such this boolean
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// flag is used. If this flag is zero, PendSV should perform a context restore.
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// If this flag is non-zero, PendSV should perform a context save.
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// Note: The smallest unit of storage is a single byte.
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//
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// NOTE: This flag must be set before PendSV is triggered!
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//------------------------------------------------------------------------------
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__BSS__
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__EXPORT__ halPendSvSaveContext
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halPendSvSaveContext:
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__SPACE__ 1
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//------------------------------------------------------------------------------
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// int32u savedMSP
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//
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// Private storage to hold the saved stack pointer. This variable is only used
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// in this file and should not be extern'ed. In our current design we
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// do not use real context switching, but only context saving and restoring.
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// As such, we only need to keep track of the Main Stack Pointer (MSP). This
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// variable is used to hold the MSP between a save and a restore.
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//------------------------------------------------------------------------------
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__BSS__
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__EXPORT__ savedMSP
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savedMSP:
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__SPACE__ 4
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//------------------------------------------------------------------------------
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// void halPendSvIsr(void)
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//
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// This ISR is installed by cstartup in the vector table for the PendSV
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// exception. The purpose of this ISR is to either save the current context
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// and trigger sleeping through the 'WFI' instruction, or restore a
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// previous context. The variable halPendSvSaveContext is used to
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// decide if a save or a restore is performed. Since entering/exiting interrupt
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// context automatically saves/restores 8 of the 16 CPU registers on the stack
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// we need to manually save the other 8 onto the stack as well.
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//
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// When a context save is complete, the stack will have been expanded by 16
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// words with the current Stack Pointer stored in savedMSP.
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//
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// When a context restore is complete, the stack will have been shrunk by 16
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// words with the old context restored after the return instruction.
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//
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// NOTE: The IAR default handler name for PendSV, PendSV_Handler, is also
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// instantiated here so it routes to the same code as the St
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// name halPendSvIsr.
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//------------------------------------------------------------------------------
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__CODE__
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__THUMB__
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__EXPORT__ PendSV_Handler
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__EXPORT__ halPendSvIsr
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PendSV_Handler:
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halPendSvIsr:
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LDR R0, =halPendSvSaveContext //load the variable's address
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LDRB R0, [R0] //get the value in the variable
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CBZ R0, contextRestore //if variable is zero, branch to contextRestore
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contextSave:
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MRS R0, MSP //load the main stack pointer into R0
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SUB R0, R0, #0x20 //make room on the stack for 8 words (32 bytes)
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MSR MSP, R0 //load new MSP from adjusted stack pointer
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STM R0, {R4-R11} //store R4-R11 (8 words) onto the stack
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LDR R1, =savedMSP //load address of savedMSP into R1
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STR R0, [R1] //store the MSP into savedMSP
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WFI //all saved, trigger deep sleep
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// Even if we fall through the WFI instruction, we will immediately
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// execute a context restore and end up where we left off with no
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// ill effects. Normally at this point the core will either be
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// powered off or reset (depending on the deep sleep level).
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contextRestore:
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LDR R0, =savedMSP //load address of savedMSP into R0
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LDR R0, [R0] //load the MSP from savedMSP
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LDM R0, {R4-R11} //load R4-R11 (8 words) from the stack
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ADD R0, R0, #0x20 //eliminate the 8 words (32 bytes) from the stack
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MSR MSP, R0 //restore the MSP from R0
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BX LR //return to the old context
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//------------------------------------------------------------------------------
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// void halTriggerContextRestore(void)
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//
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// Cstartup is responsible for triggering a context restore based upon the
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// RESET_EVENT register. Since the stack pointer sits at the top of memory
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// after the core boots, cstartup cannot simply trigger a PendSV to restore
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// context as this will cause existing stack data to be over written. Cstartup
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// disables interrupts, pends PendSV, and then calls this function. This
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// function simply configures the Stack Pointer to be past the previous data
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// such that when interrupts are enabled and PendSV fires it wont corrupt
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// previous data.
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//------------------------------------------------------------------------------
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__CODE__
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__THUMB__
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__EXPORT__ halTriggerContextRestore
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halTriggerContextRestore:
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LDR R0, =savedMSP //load address of savedMSP into R0
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LDR R0, [R0] //load the MSP from savedMSP
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MSR MSP, R0 //restore the MSP from R0
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CPSIE i //enable interrupts and let PendSV fire
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BX LR //this return should never be triggered
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//------------------------------------------------------------------------------
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// void halInternalIdleSleep(void)
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//
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// A simple internal function call (to be called from halSleep) for executing
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// the WFI instruction and entering the simple, idle sleep state.
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//------------------------------------------------------------------------------
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__CODE__
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__THUMB__
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__EXPORT__ halInternalIdleSleep
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halInternalIdleSleep:
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WFI //trigger idle sleep
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BX LR //return
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__END__
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