; ;******************************************************************************************************** ; uC/OS-III ; The Real-Time Kernel ; ; ; (c) Copyright 2009-2010; Micrium, Inc.; Weston, FL ; All rights reserved. Protected by international copyright laws. ; ; ARM Cortex-M3 Port ; ; File : OS_CPU_A.ASM ; Version : V3.01.2 ; By : JJL ; BAN ; ; For : ARMv7M Cortex-M3 ; Mode : Thumb2 ; Toolchain : IAR EWARM ;******************************************************************************************************** ; ;******************************************************************************************************** ; PUBLIC FUNCTIONS ;******************************************************************************************************** EXTERN OSRunning ; External references EXTERN OSPrioCur EXTERN OSPrioHighRdy EXTERN OSTCBCurPtr EXTERN OSTCBHighRdyPtr EXTERN OSIntExit EXTERN OSTaskSwHook EXTERN OS_CPU_ExceptStkBase EXPORT OSStartHighRdy ; Functions declared in this file EXPORT OS_CPU_PendSVHandler ;PAGE ;******************************************************************************************************** ; EQUATES ;******************************************************************************************************** NVIC_INT_CTRL EQU 0xE000ED04 ; Interrupt control state register. NVIC_SYSPRI14 EQU 0xE000ED22 ; System priority register (priority 14). NVIC_PENDSV_PRI EQU 0xFF ; PendSV priority value (lowest). NVIC_PENDSVSET EQU 0x10000000 ; Value to trigger PendSV exception. ;******************************************************************************************************** ; CODE GENERATION DIRECTIVES ;******************************************************************************************************** ;RSEG CODE:CODE:NOROOT(2) ;THUMB PRESERVE8 AREA |.text|,CODE,READONLY THUMB ;PAGE ;******************************************************************************************************** ; START MULTITASKING ; void OSStartHighRdy(void) ; ; Note(s) : 1) This function triggers a PendSV exception (essentially, causes a context switch) to cause ; the first task to start. ; ; 2) OSStartHighRdy() MUST: ; a) Setup PendSV exception priority to lowest; ; b) Set initial PSP to 0, to tell context switcher this is first run; ; c) Set the main stack to OS_CPU_ExceptStkBase ; d) Trigger PendSV exception; ; e) Enable interrupts (tasks will run with interrupts enabled). ;******************************************************************************************************** OSStartHighRdy LDR R0, =NVIC_SYSPRI14 ; Set the PendSV exception priority LDR R1, =NVIC_PENDSV_PRI STRB R1, [R0] MOVS R0, #0 ; Set the PSP to 0 for initial context switch call MSR PSP, R0 LDR R0, =OS_CPU_ExceptStkBase ; Initialize the MSP to the OS_CPU_ExceptStkBase LDR R1, [R0] MSR MSP, R1 LDR R0, =NVIC_INT_CTRL ; Trigger the PendSV exception (causes context switch) LDR R1, =NVIC_PENDSVSET STR R1, [R0] CPSIE I ; Enable interrupts at processor level OSStartHang B OSStartHang ; Should never get here ;PAGE ;******************************************************************************************************** ; HANDLE PendSV EXCEPTION ; void OS_CPU_PendSVHandler(void) ; ; Note(s) : 1) PendSV is used to cause a context switch. This is a recommended method for performing ; context switches with Cortex-M3. This is because the Cortex-M3 auto-saves half of the ; processor context on any exception, and restores same on return from exception. So only ; saving of R4-R11 is required and fixing up the stack pointers. Using the PendSV exception ; this way means that context saving and restoring is identical whether it is initiated from ; a thread or occurs due to an interrupt or exception. ; ; 2) Pseudo-code is: ; a) Get the process SP, if 0 then skip (goto d) the saving part (first context switch); ; b) Save remaining regs r4-r11 on process stack; ; c) Save the process SP in its TCB, OSTCBCurPtr->OSTCBStkPtr = SP; ; d) Call OSTaskSwHook(); ; e) Get current high priority, OSPrioCur = OSPrioHighRdy; ; f) Get current ready thread TCB, OSTCBCurPtr = OSTCBHighRdyPtr; ; g) Get new process SP from TCB, SP = OSTCBHighRdyPtr->OSTCBStkPtr; ; h) Restore R4-R11 from new process stack; ; i) Perform exception return which will restore remaining context. ; ; 3) On entry into PendSV handler: ; a) The following have been saved on the process stack (by processor): ; xPSR, PC, LR, R12, R0-R3 ; b) Processor mode is switched to Handler mode (from Thread mode) ; c) Stack is Main stack (switched from Process stack) ; d) OSTCBCurPtr points to the OS_TCB of the task to suspend ; OSTCBHighRdyPtr points to the OS_TCB of the task to resume ; ; 4) Since PendSV is set to lowest priority in the system (by OSStartHighRdy() above), we ; know that it will only be run when no other exception or interrupt is active, and ; therefore safe to assume that context being switched out was using the process stack (PSP). ;******************************************************************************************************** OS_CPU_PendSVHandler CPSID I ; Prevent interruption during context switch MRS R0, PSP ; PSP is process stack pointer CBZ R0, OS_CPU_PendSVHandler_nosave ; Skip register save the first time SUBS R0, R0, #0x20 ; Save remaining regs r4-11 on process stack STM R0, {R4-R11} LDR R1, =OSTCBCurPtr ; OSTCBCurPtr->OSTCBStkPtr = SP; LDR R1, [R1] STR R0, [R1] ; R0 is SP of process being switched out ; At this point, entire context of process has been saved OS_CPU_PendSVHandler_nosave PUSH {R14} ; Save LR exc_return value LDR R0, =OSTaskSwHook ; OSTaskSwHook(); BLX R0 POP {R14} LDR R0, =OSPrioCur ; OSPrioCur = OSPrioHighRdy; LDR R1, =OSPrioHighRdy LDRB R2, [R1] STRB R2, [R0] LDR R0, =OSTCBCurPtr ; OSTCBCurPtr = OSTCBHighRdyPtr; LDR R1, =OSTCBHighRdyPtr LDR R2, [R1] STR R2, [R0] LDR R0, [R2] ; R0 is new process SP; SP = OSTCBHighRdyPtr->StkPtr; LDM R0, {R4-R11} ; Restore r4-11 from new process stack ADDS R0, R0, #0x20 MSR PSP, R0 ; Load PSP with new process SP ORR LR, LR, #0x04 ; Ensure exception return uses process stack CPSIE I BX LR ; Exception return will restore remaining context END