request_threaded_irq

Name

request_threaded_irq — allocate an interrupt line

Synopsis

int fsfuncrequest_threaded_irq (	unsigned int irq,
	irq_handler_t handler,
	irq_handler_t thread_fn,
	unsigned long irqflags,
	const char * devname,
	void * dev_id);

 

Arguments

irq

Interrupt line to allocate

handler

Function to be called when the IRQ occurs. Primary handler for threaded interrupts If NULL and thread_fn != NULL the default primary handler is installed

thread_fn

Function called from the irq handler thread If NULL, no irq thread is created

irqflags

Interrupt type flags

devname

An ascii name for the claiming device

dev_id

A cookie passed back to the handler function

Description

This call allocates interrupt resources and enables the interrupt line and IRQ handling. From the point this call is made your handler function may be invoked. Since your handler function must clear any interrupt the board raises, you must take care both to initialise your hardware and to set up the interrupt handler in the right order.

If you want to set up a threaded irq handler for your device then you need to supply handler and thread_fn. handler ist still called in hard interrupt context and has to check whether the interrupt originates from the device. If yes it needs to disable the interrupt on the device and return IRQ_WAKE_THREAD which will wake up the handler thread and run thread_fn. This split handler design is necessary to support shared interrupts.

Dev_id must be globally unique. Normally the address of the device data structure is used as the cookie. Since the handler receives this value it makes sense to use it.

If your interrupt is shared you must pass a non NULL dev_id as this is required when freeing the interrupt.

Flags

IRQF_SHARED Interrupt is shared IRQF_SAMPLE_RANDOM The interrupt can be used for entropy IRQF_TRIGGER_* Specify active edge(s) or level

分析request_threaded_irq()函数中的各个形参
1>：irq:表示申请的中断号。
2>：handler:表示中断服务例程
3.> thread_fn：中断线程化，此处传递的是NULL。NULL表示没有中断线程化。
此参数是最新版本中才出现的。为什么要提出中断线程化?
在 Linux 中，中断具有最高的优先级。不论在任何时刻，只要产生中断事件，内核将立即执行相应的中断
处理程序，等到所有挂起的中断和软中断处理完毕后才能执行正常的任务，因此有可能造成实时任务得不
到及时的处理。中断线程化之后，中断将作为内核线程运行而且被赋予不同的实时优先级，实时任务可以
有比中断线程更高的优先级。这样，具有最高优先级的实时任务就能得到优先处理，即使在严重负载下仍
有实时性保证。but,并不是所有的中断都可以被线程化，比如时钟中断，主要用来维护系统时间以及定时器
等，其中定时器是操作系统的脉搏，一旦被线程化，就有可能被挂起，这样后果将不堪设想，所以不应当
被线程化。 
4>.irqflags:表示中断标志位。
5>.devname:表示请求中断的设备的名称。

6>.dev_id: 对应于request_irq()函数中所传递的第五个参数，可取任意值，但必须唯一能够代表发出中断请求的设备，通常取描述该设备的结构体。 共享中断时所用。