threadx操作系统_threadx usb_threadx缺点(3)

; addition, IRQ interrupts may be re-enabled - with certain restrictions -

; if nested IRQ interrupts are desired. Interrupts may be re-enabled over

; small code sequences where lr is saved before enabling interrupts and

; restored after interrupts are again disabled. */

;

;

; The myIrqHander is written without support for nested interrupts, so it

; is called before the nested interrupt support code.

;

BLX myIrqHander

;

; /* Interrupt nesting is allowed after calling _tx_thread_irq_nesting_start

; from IRQ mode with interrupts disabled. This routine switches to the

; system mode and returns with IRQ interrupts enabled.

;

; NOTE: It is very important to ensure all IRQ interrupts are cleared

; prior to enabling nested IRQ interrupts. */

IF :DEF:TX_ENABLE_IRQ_NESTING

BL _tx_thread_irq_nesting_start

ENDIF

;

;

; /* Application IRQ handlers can be called here! */

;

; /* If interrupt nesting was started earlier, the end of interrupt nesting

; service must be called before returning to _tx_thread_context_restore.

; This routine returns in processing in IRQ mode with interrupts disabled. */

IF :DEF:TX_ENABLE_IRQ_NESTING

BL _tx_thread_irq_nesting_end

ENDIF

;

; /* Jump to context restore to restore system context. */

B _tx_thread_context_restore

; end of _irq_handler

其中myIrqHander为C代码的入口函数，在IRQ中断发生时执行上面的汇编代码，保存上下文，

最后跳转到 BLX myIrqHander，开始myIrqHander()函数的执行。

/**

*

* @Name: myIrqHander()

*

* @Description: This is the 'C' entry for the IRQ interrupt handler. This is

* called from assembly to process all ARM IRQ interrupts and all

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