Visible to Intel only — GUID: iga1457465685895
Ixiasoft
Visible to Intel only — GUID: iga1457465685895
Ixiasoft
38.6.2.1. alt_ic_isr_register() versus alt_irq_register()
The enhanced API function alt_ic_isr_register() is very similar to the legacy function alt_irq_register(), with a few important differences. The differences between these two functions are best understood by examining the code in Registering an ISR with Both APIs. This example registers a timer interrupt in either the legacy API or the enhanced API, whichever is implemented in the board support package (BSP). The example is taken directly from the example code accompanying this document.
Registering an ISR with Both APIs
#ifdef ALT_ENHANCED_INTERRUPT_API_PRESENT
void timer_interrupt_latency_init (void* base, alt_u32 irq_controller_id, alt_u32 irq)
{
/* Register the interrupt */
alt_ic_isr_register(irq_controller_id, irq, timer_interrupt_latency_irq, base, NULL);
/* Start timer */
IOWR_ALTERA_AVALON_TIMER_CONTROL(base, ALTERA_AVALON_TIMER_CONTROL_ITO_MSK
| ALTERA_AVALON_TIMER_CONTROL_START_MSK);
}
#else
void timer_interrupt_latency_init (void* base, alt_u32 irq)
{
/* Register the interrupt */
alt_irq_register(irq, base, timer_interrupt_latency_irq);
/* Start timer */
IOWR_ALTERA_AVALON_TIMER_CONTROL(base, ALTERA_AVALON_TIMER_CONTROL_ITO_MSK
| ALTERA_AVALON_TIMER_CONTROL_START_MSK);
}
#endif
The first line of Registering an ISR with Both APIs detects whether the BSP implements the enhanced interrupt API. If the enhanced API is implemented, the timer_interrupt_latency_init() function calls the enhanced function. If not, timer_interrupt_latency_init() reverts to the legacy interrupt API function.
For an explanation of how the Nios® II Software Build Tools select which API to implement in a BSP, refer to “Interrupt Service Routines” in the Exception Handling chapter of the Nios® II Software Developer’s Handbook.
Enhanced Function alt_ic_isr_register() shows the function prototype for alt_ic_isr_register(), which registers an ISR in the enhanced API. The interrupt controller identifier (for argument ic_id) and the interrupt port number (for argument irq) are defined in system.h.
Enhanced Function alt_ic_isr_register()
extern int alt_ic_isr_register(alt_u32 ic_id,
alt_u32 irq,
alt_isr_func isr,
void *isr_context,
void *flags);
For comparison, Legacy Function alt_irq_register() shows the function prototype for alt_irq_register(), which registers an ISR in the legacy API.
Legacy Function alt_irq_register()
extern int alt_irq_register (alt_u32 id,
void* context,
alt_isr_func handler);
The arguments passed into alt_ic_isr_register() are slightly different from those passed into alt_irq_register(). The table below compares the arguments to the two functions.
alt_ic_isr_register() Argument | Purpose | alt_irq_register() Argument |
---|---|---|
alt_u32 ic_id | Unique interrupt controller ID as defined in system.h. | — |
alt_u32 irq | Interrupt request (IRQ) number as defined in system.h. | alt_u32 id |
alt_isr_func isr | Interrupt service routine (ISR) function pointer | handler |
void* isr_context | Optional pointer to a component-specific data structure. | context |
void* flags | Reserved. Other EIC implementations might use this argument. | None |
There are other significant differences between the legacy interrupt API and the enhanced interrupt API. Some of these differences impact the ISR body itself. Notably, the two APIs employ completely different interrupt preemption models. The example code accompanying this document illustrates many of the differences.
For further information about the other functions in the HAL interrupt APIs, refer to the Exception Handling and HAL API Reference chapters of the Nios® II Software Developer’s Handbook.