diff options
Diffstat (limited to 'portable/GCC/ARM_CM0/port.c')
| -rw-r--r-- | portable/GCC/ARM_CM0/port.c | 58 |
1 files changed, 50 insertions, 8 deletions
diff --git a/portable/GCC/ARM_CM0/port.c b/portable/GCC/ARM_CM0/port.c index 93e6d0489..53bc33a41 100644 --- a/portable/GCC/ARM_CM0/port.c +++ b/portable/GCC/ARM_CM0/port.c @@ -34,6 +34,9 @@ #include "FreeRTOS.h" #include "task.h" +/* Prototype of all Interrupt Service Routines (ISRs). */ +typedef void ( * portISR_t )( void ); + /* Constants required to manipulate the NVIC. */ #define portNVIC_SYSTICK_CTRL_REG ( *( ( volatile uint32_t * ) 0xe000e010 ) ) #define portNVIC_SYSTICK_LOAD_REG ( *( ( volatile uint32_t * ) 0xe000e014 ) ) @@ -51,6 +54,10 @@ #define portNVIC_PENDSV_PRI ( portMIN_INTERRUPT_PRIORITY << 16UL ) #define portNVIC_SYSTICK_PRI ( portMIN_INTERRUPT_PRIORITY << 24UL ) +/* Constants used to check the installation of the FreeRTOS interrupt handlers. */ +#define portSCB_VTOR_REG ( *( ( portISR_t ** ) 0xe000ed08 ) ) +#define portVECTOR_INDEX_PENDSV ( 14 ) + /* Constants required to set up the initial stack. */ #define portINITIAL_XPSR ( 0x01000000 ) @@ -200,20 +207,20 @@ void vPortSVCHandler( void ) void vPortStartFirstTask( void ) { - /* The MSP stack is not reset as, unlike on M3/4 parts, there is no vector - * table offset register that can be used to locate the initial stack value. - * Not all M0 parts have the application vector table at address 0. */ + /* Don't reset the MSP stack as is done on CM3/4 devices. The vector table + * in some CM0 devices cannot be modified and thus may not hold the + * application's initial MSP value. */ __asm volatile ( " .syntax unified \n" " ldr r2, pxCurrentTCBConst2 \n" /* Obtain location of pxCurrentTCB. */ " ldr r3, [r2] \n" " ldr r0, [r3] \n" /* The first item in pxCurrentTCB is the task top of stack. */ - " adds r0, #32 \n" /* Discard everything up to r0. */ - " msr psp, r0 \n" /* This is now the new top of stack to use in the task. */ + " adds r0, #32 \n" /* Discard everything up to r0. */ + " msr psp, r0 \n" /* This is now the new top of stack to use in the task. */ " movs r0, #2 \n" /* Switch to the psp stack. */ - " msr CONTROL, r0 \n" + " msr CONTROL, r0 \n" " isb \n" - " pop {r0-r5} \n" /* Pop the registers that are saved automatically. */ + " pop {r0-r5} \n" /* Pop the registers that are saved automatically. */ " mov lr, r5 \n" /* lr is now in r5. */ " pop {r3} \n" /* Return address is now in r3. */ " pop {r2} \n" /* Pop and discard XPSR. */ @@ -231,7 +238,42 @@ void vPortStartFirstTask( void ) */ BaseType_t xPortStartScheduler( void ) { - /* Make PendSV, CallSV and SysTick the same priority as the kernel. */ + /* An application can install FreeRTOS interrupt handlers in one of the + * folllowing ways: + * 1. Direct Routing - Install the function xPortPendSVHandler for PendSV + * interrupt. + * 2. Indirect Routing - Install separate handler for PendSV interrupt and + * route program control from that handler to xPortPendSVHandler function. + * + * Applications that use Indirect Routing must set + * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct + * routing, which is validated here when configCHECK_HANDLER_INSTALLATION + * is 1, should be preferred when possible. */ + #if ( configCHECK_HANDLER_INSTALLATION == 1 ) + { + /* Point pxVectorTable to the interrupt vector table. Systems without + * a VTOR register provide the value zero in the VTOR register and + * the vector table itself is located at the address 0x00000000. */ + const portISR_t * const pxVectorTable = portSCB_VTOR_REG; + + /* Validate that the application has correctly installed the FreeRTOS + * handler for PendSV interrupt. We do not check the installation of the + * SysTick handler because the application may choose to drive the RTOS + * tick using a timer other than the SysTick timer by overriding the + * weak function vPortSetupTimerInterrupt(). + * + * Assertion failures here indicate incorrect installation of the + * FreeRTOS handler. For help installing the FreeRTOS handler, see + * https://www.FreeRTOS.org/FAQHelp.html. + * + * Systems with a configurable address for the interrupt vector table + * can also encounter assertion failures or even system faults here if + * VTOR is not set correctly to point to the application's vector table. */ + configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler ); + } + #endif /* configCHECK_HANDLER_INSTALLATION */ + + /* Make PendSV and SysTick the lowest priority interrupts. */ portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI; portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI; |