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From: Ho Tam <mophong@gmail.com>
Date: Thu, 9 Aug 2018 00:41:43 +0900
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Subject: Re: [Xenomai] Xenomai on Raspberry pi 2,
 3 - Userspace task is interrupted?
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To: greg@embeddedgreg.com
Cc: xenomai@xenomai.org

I used bcm2835 library for test, that library is implemented using memory
map (mmap). You may check its copied code here:
https://github.com/smart-facility/bcm2835/tree/master/src
The function I used  bcm2835_gpio_write:
void bcm2835_gpio_write(uint8_t pin, uint8_t on)
{
    if (on)
bcm2835_gpio_set(pin);
    else
bcm2835_gpio_clr(pin);
}

I have also tested by direct using of bcm2835_gpio_set and bcm2835_gpio_clr
fucntions, but result was same as previous test:
for (i=0; i<500; ++i)
{
bcm2835_gpio_set(TEST_PIN);
bcm2835_gpio_clr(TEST_PIN);
}

Since functions in bcm2835 library usually call many other functions, I
have also implemented my own gpio library which directly read/write value
to GPSET and GPCLR:
for (i=0; i<3000; ++i)
{
*(rpi_gpio_mem_base+7) =(1<<TEST_PIN);    //rpi_gpio_mem_base+7 ~ GPSET0
*(rpi_gpio_mem_base+10) =(1<<TEST_PIN);  //rpi_gpio_mem_base+10 ~ GPCLR0
}
Here rpi_gpio_mem_base has been initialized with mmap before. In this case,
both process time and worst time reduce (for sure). But again, worst time
on rpi2,3 is larger than 350% process time, while for rpi0,1 worst time ~
120% process time.
Regards,


On Wed, Aug 8, 2018 at 8:12 PM Greg Gallagher <greg@embeddedgreg.com> wrote:

>
> How are you setting up the gpio read and write? Is it possible to post a
> code snippet for the read and write?
>
> Greg
>
>   Original Message
> From: mophong@gmail.com
> Sent: August 8, 2018 6:45 AM
> To: xenomai@xenomai.org
> Reply-to: mophong@gmail.com
> Subject: [Xenomai] Xenomai on Raspberry pi 2, 3 - Userspace task is
> interrupted?
>
> Hello all,
> I make a simple code to measure process time on Raspberry pi 0,1,2,3 like:
>
> * previous = rt_timer_read();*
> * for (i=0; i<500; ++i)*
> * {*
> * bcm2835_gpio_write(TEST_PIN, HIGH);*
> * bcm2835_gpio_write(TEST_PIN, LOW);*
> * }*
> * now = rt_timer_read();*
> * process_time = (long) (now - previous);*
> * if (process_time>worst_time)*
> * worst_time=process_time;*
>
> And I result after several hours running:
> rpi           process_time (us)             worst_time (us)
> 0,1           ~100                                     115
> 2,3           ~90                                        373
>
> It is clear that process time on rpi2,3 is shorter than that on rpi0,1 due
> to higher speed CPU. However, I don't understand why worst case on rpi2,3
> is much larger than that on rpi0,1. I have repeated this test on both
> xenomai 2 and 3, kernel  4.1 and 4.9 (only xenomai 3 in this case) and with
> different task priority, the result is quite consistent.
> Does anyone have explanation and solution?
> Thanks and regards,
> _______________________________________________
> Xenomai mailing list
> Xenomai@xenomai.org
> https://xenomai.org/mailman/listinfo/xenomai
>


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