Re: [Adeos-main] interrupt latency

[Philippe Gerum <rpm@xenomai.org>]

On Mon, 2004-02-23 at 00:35, Dirk Roloff wrote:
> Hi List,
> 
> I ve got the following problem:
> 
> I have to write a driver for linux for a receiver-board. 
> On this board is an AMCC S5933 pci-controler. Ok on this chip is a fifo (256 
> bit).
> it has 2 regsiters MWAR (adress for DMA) and MWTC ( byte count for DMA)
> i will set both to a buffer - the count will be decemented and if it reaches 
> zero i will get an interrupt (IRQ 5). in the drivers handler function i will 
> just set MWAR to the next buffer and MWTC to the size of the buffer.
> So the board can start new DMA.
> 
> Thats the background now the problem:
> the fifo, again its 256 bit will be filled by a satalite link with 1Mbit
> 1024000 bits per second. So i have a maximum of 0.25 milliseconds.
> and i have no idea how long it takes to get the pci for the next dma.
> But it woks most time, but ca. 10 times in an hour my pc is too slow.
> ( i think - i am not sure )
> So i loose some data. Its a receive only application so i have no handshake 
> back in the air.
> 
> if you google for interrupt latency - you will find "Linux is no RTOS" - so i 
> find rtai and the adeos-patches. Great that sounds like it could work.
> untar kernel - patch - compile - crash - compile - read ... read ... 
> understand ... ahhhh .... ok i changed the driver.
> 
> Create a domain with prio 200 
> adeos_virtualize_irq( IRQ 5 )
> compile - test .... the same problem .... i lose data ....
> 
> My next try to understand whats going on .... create a new module to simulate 
> what i think is going on.
> i put some soure at the end of this mail.
> 
> I registered a linux handler vor irq 4 (serial device)
> this is just looping in a long loop doing nothing but using cpu power.
> ( a cat on ttyS0 will trigger one irq )
> 
> i register a handler for all (0-15) irqs on the realtimeside.
> while the linux handler is running i am counting the irqs that will be entered 
> in there.
> 
> at the end of the linux_handler i printk what is captured by the realtime:
> IRQ 0 ( timer i think ) 300 times and more ...
> 
> and then i see only one other IRQ happening once !!
> IRQ 9 ( scsii ) or IRQ 1 (keyboard) or IRQ 12 (mouse)
> 
> realy - when i trigger IRQ 4 ( by cat /dev/ttyS0 ) the pc is hanging for about 
> a sekond. i am spinning around the mouse and pressing the keyboard.
> i will only catch one IRQ.
> 
> At the end of the linux handler i read out the pic. the catched irq for 
> example 12 is marked out. And i couldn't find why. If i understand the code. 
> an incomming IRQ will be acked and put in the ipipe. So new IRQs can happen.
> While walking down the ipipe.
> 
> Back to my real problem - if there is a driver on the linux side - the ide or 
> whatever using long time ( simulated by IRQ 4 ) i will not get in the 
> realtime handler for my receiver card.
> 
> My goal is: if IRQ 5 is raised - stop doing what ever you are doing - serve 
> the board, and after that you have all time you need.
> 
> i am working a week on my own, its sunday night and the weekend is also gone.
> i real need someone to help me.
> 
> thanks
> 
> Dirk
> 
> ah ... here is now the code pices ( I cut out some stuff )
> 
> 
> init_module()
>  - request_irq( 4 , linux_handler ) /* my simulation of a long running device 
> handler here ist ttyS0 */
>  - adeos_register_domain( myRealtime )
> 
> in the DomainEntry()
> {
>  int i;
>   for(i=0;i<16;++i) adeos_virtualize_irq( i realtime_handler )
> 

It would be interesting to know the flags passed to
adeos_virtualize_irq(). In any case, either the 4th arg should pass
IPIPE_PASS_MASK, or you realtime_handler() routine should call
adeos_propagate_irq(irq).

>   for(;;) /* dont realy understand - copyed from rtai */
>     adeos_suspend_domain();
> }
> 
> static volatile int linux_irq = 0;
> static volatile int irq_count[256];
> 
> static void linux_handler()
> {
>   linux_irq = 1;	/* we are running */
>  /* just eating some cpu time - this will hang the linux for 1-2 sekonds */
>   for(x=0;x<1000;++x) 
>     for(i=0;i<1000000;++i)
>       if( x==0)++i;

>   linux_irq = 0; /* we are finish */
>   /* Ok lets have a look what happend in realtime */
>   for( i=0;i<255;++i)
>   {
>     if( irq_count[i] != 0)
>       printk ("linux_irq_handler: irq %d catched %d times\n",i ,irq_count[i]);
>   }
> }
> 
> static void 
> realtime_handler ( unsigned int irq )
> {
>   if(linux_irq != 0)
>   {
>     ++irq_count[irq]; /* add counter while linux_handler is running */
>   }
> }
> 
> 
> 
> 
> 
> 
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-- 

Philippe.