Re: [Xenomai-help] parallelport module for measuring external interrupt latency

[Jan Kiszka <jan.kiszka@domain.hid>]

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Markus Franke wrote:
> Dear Xenomai-Users / Developers,
> 
> I have finished my work on a parallelport module for measuring external
> interrupt latencies. It is based on another kernel-module working on
> plain linux. Interrupt latencies are measured via triggering an
> interrupt over a connection between data pin 7 and the ACK-pin.
> 
> The kernel module loads fine without any problems. When starting the
> User-space task the system freezes without any output in the kernel log.
>  I was trying to solve the problem for several days now without any
> success. I would appreciate, if somebody would have a short look on it.
> Maybe its just a small problem which can be fixed easily.
> 
> The kernel-module as well as the user-space task are attached.
> 
> Thanks in advance and regards,
> Markus Franke
> 
> PS.: I am aware of the fact that there is already a testcase in the
> testsuite for measuring external interrupt latencies. Nevertheless, I
> would like to gain experiences in developing with Xenomai and I want to
> know why the attached code doesn't work. I will also work with the
> testcases in the testsuite soon.
> 

...

> 
> // ISR
> int parport_isr(xnintr_t* cookie)
> {
> 	rdtsc(t_end);
> 	
> 	outb(0x00,SPPDATAPORT);
> 	
> #ifdef DEBUG
> 	printk(KERN_INFO "parport_latency: Interrupt fired!!!\n");
> 	printk(KERN_INFO "parport_latency: interruptcount before = %d!!!\n",atomic_read(&interruptcount));
> #endif
> 	
> 	atomic_inc(&interruptcount);
> 
> #ifdef DEBUG
> 	printk(KERN_INFO "parport_latency: interruptcount after= %d!!!\n",atomic_read(&interruptcount));
> #endif
> 
> 	wake_up_interruptible(&intlatpar_queue);

This is a hard-RT IRQ handler, thus any scheduling Linux service is
strictly forbidden.

[Reminds me of the I-pipe debugging service that can catch such faults
but still needs some integration work...]

> 
> #ifdef DEBUG
> 	printk(KERN_INFO "parport_latency: exit parport_isr()!!!\n");
> #endif
> 
> 	return 0;
> }
> 
> /* the struct of fileoperations */
> static struct file_operations intlat_fops = {
> 	.read = latdev_read,
> 	.open = latdev_open,
> 	.release = latdev_release,
> 	.ioctl = latdev_ioctl
> };
> 
> 
> // Initialise module
> int parport_init(void)
> {
> 	int err = 0;
> 	
> 	printk(KERN_INFO "parport_latency: Initialisation started\n");
> 	
> 	/* enable parallel port interrupt generation, probably not needed */
>         outb(SSPINTERRUPTENABLE,SPPCONTROLPORT);
> 	
> 	err = rt_intr_create(&intr, "parport_latency", INTR_NR, &parport_isr, NULL, 0);
> 	if(err != 0)
> 	{
> 		printk(KERN_INFO "parport_latency: Error while requesting Interrupt %d, error %d\n", INTR_NR, err);
> 		return -1;
> 	}
> 
> 	err = rt_intr_enable(&intr);
> 	if(err != 0)
> 	{
> 		printk(KERN_INFO "parport_latency: Error while enabling Interrupt %d, error %d\n", INTR_NR, err);
> 		return -1;
> 	}
> 
> 	if(register_chrdev(INTLAT_DEV_MAJOR,INTLAT_DEV_NAME,&intlat_fops) < 0) 
> 	{
> 		printk(KERN_WARNING "intlat: parport_latency(): register_chrdev() failed.\n");
> 		rt_intr_disable(&intr);
> 		return -1;
> 	}

Hmm, a Linux character device for this purpose... I guess you should
study the existing irqbench test a bit first. And if you don't see why
something is done the way it is - ask here.

Jan


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