Posted on May 17, 2011 at 13:21Hi,
I've been going through the forum for an answer to the following question but was unable to find it... I would appreciate it if someone could help me out.
Q) I am trying to understand the difference between the NVIC_SystemHandlerPriorityConfig and the NVIC_PriorityGroupConfig. As I understand, the STM32 has 4 bits for external interrupts. Which is 16 priority levels (Preemption + Subpriority) and can be manipulated via NVIC_PriorityGroupConfig function. The NVIC_SystemHandlerPriorityConfig will set the
System Handlers Priority Register [31:24].
Code:
// 0xE000ED20 - SysTick (PRI_15)
NVIC_SystemHandlerPriorityConfig(SystemHandler_SysTick, 0, 0);
Application Interrupt and Reset Control Register [10:8]Priority Group
7 -> NVIC_PriorityGroup_0 [0 bits preemption, 4 bits subpriority]
Priority Group
6 -> NVIC_PriorityGroup_1 [1 bits preemption, 3 bits subpriority]
Priority Group
5 -> NVIC_PriorityGroup_2 [2 bits preemption, 2 bits subpriority]
Priority Group
4 -> NVIC_PriorityGroup_3 [3 bits preemption, 1 bits subpriority]
Priority Group
3 -> NVIC_PriorityGroup_4 [4 bits preemption, 0 bits subpriority]
The System Handler SysTick has 8 bits for priority settings, and the external interrupts has 4 bits. How are they related?
Code:
// Resets the NVIC registers to their default reset value
NVIC_DeInit();
// Resets the SCB registers to their default reset value
NVIC_SCBDeInit();
// Configure the Priority Grouping with 2 bits for preemption and 2 bits for subpriority
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);
// Enable SysTick System interrupt with Preemption Priority 0 and SubPriority as 0
NVIC_SystemHandlerPriorityConfig(SystemHandler_SysTick, 0, 0);
// Enable USB Global interrupt with Preemption Priority 0 and SubPriority as 1
NVIC_InitStructure.NVIC_IRQChannel = USB_LP_CAN_RX0_IRQChannel;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
// Enable USART1 Global interrupt with Preemption Priority 0 and SubPriority as 2
NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQChannel;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
// Enable USART2 Global interrupt with Preemption Priority 0 and SubPriority as 1
NVIC_InitStructure.NVIC_IRQChannel = USART2_IRQChannel;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
SysTick has the highest priority and USART2 has the lowest. If SysTick and USB_LP occurs at the sametime, SysTick is selected. If USART1 and USART2 occurs at the sametime, USART1 is selected. If SysTick and USART1 occurs, SysTick is selected.
Have I understood this correctly or I messed it up? :p
Thanks for your comments.
-Mad
