use of /dev/gpiomem for non root usage

[Marc-Antoine Brenac]

Since the first Lenny base version of raspbian they have add some special mapping for gpio access without the need to be root.

see here : 

https://www.raspberrypi.org/blog/raspbian-jessie-is-here/

https://github.com/raspberrypi/linux/pull/1112

Is there any plan to implement it in libbcm2835 ?

It would be so helpfull, even if it supports fewer features.

See you,

Marc-Antoine

[Mike McCauley]

Hello,

the new /dev/gpiomem only exposes the GPIO pin access, but bcm2835 also
supports PWM, I2C and SPI peripherals. So supporting /dev/gpiomem does not
really fit well with the current design of bcm2835.

Cheers.

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Airspayce Pty Ltd 9 Bulbul Place Currumbin Waters QLD 4223 Australia
http://www.airspayce.com
Phone +61 7 5598-7474

[Marc-Antoine Brenac]

thx for your answer, I get totally it.

 

what if I just change the path in the lib, Do you think it will work fro GPIO at least ? or do I have to redo the mapping ?

any guess.

Marc-Antoine BRENAC
+33.687507577

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[Mike McCauley]

Hi,

On Friday, February 26, 2016 08:19:27 AM Marc-Antoine Brenac wrote:
> thx for your answer, I get totally it.
>
> what if I just change the path in the lib, Do you think it will work fro
> GPIO at least ? or do I have to redo the mapping ?

I dont think it will be that simple.

:-(

Cheers.

[Mike McCauley]

New version 1.50 now supports starting as non-root and opening /dev/gpiomem,
for GPIO access only.

Cheers.

On Friday, February 26, 2016 08:19:27 AM Marc-Antoine Brenac wrote:

[Ron]

Hi Mike,

I am really not 100% on this stuff. What does this mean when it comes
to using the I2C interface (and such)?

73
Ron / W4MMP

[Mike McCauley]

Hi,

On Saturday, February 27, 2016 10:56:31 PM 'Ron' via bcm2835 wrote:
> Hi Mike,
>
> I am really not 100% on this stuff. What does this mean when it comes
> to using the I2C interface (and such)?

You still need to be root to use anything other than the GPIO interface, such
as SPI, I2C etc.

This is explained in the doc in the new release.

Cheers.

>
> 73
> Ron / W4MMP
>
> On 2/27/2016 22:29, Mike McCauley wrote:
> > New version 1.50 now supports starting as non-root and opening
> > /dev/gpiomem, for GPIO access only.

[Ron]

Hi Mike,

I suspected that would be the case, but wanted to be sure.

Thanks,

73
Ron / W4MMP

[Marc-Antoine Brenac]

Thanks Mike,

I'm eager to test it !

[Ron]

Hi Mike,

When using gpio I still receive: bcm2835_init: Unable to open
/dev/gpiomem: Permission denied. Would you be so kind as to pass along
the contents of your /etc/apt/sources.list ? I think I have a messed
up version of Jessie. I have been using Jessie from when it was first
available (as announced last year sometime on the Raspberry forum).

Here is my sources.list
deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib
non-free rpi

I may be picking up the release from the wrong location.

73
Ron / W4MMP

On 2/27/2016 22:29, Mike McCauley wrote:

[Marc-Antoine Brenac]

did you add pi to group gpio ?

sudo adduser pi gpio

Marc-Antoine BRENAC
+33.687507577

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[Ron]

Hi,

Thanks for the tip, but it didn't help.

73
Ron / W4MMP

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[Ron]

Hi,

I'm pretty sure I have a munged up version of Jessie.  I'm will start from scratch with the foundations version of Jessie and see what happens. 

73
Ron / W4MMP

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[Ron]

Hi,

Well, I started from scratch, installed the Raspbian / Jessie,  recompiled and installed bcm2835 and then recompiled my application. 
The application only uses GPIO.  Now the application now produces a Segmentation fault when running as a non root user.  Running it as root, the application runs fine.  When debugging the application with gdb, I get this:

Program received signal SIGSEGV, Segmentation fault.
bcm2835_peri_read (paddr=0x7) at bcm2835.c:123

73
Ron / W4MMP 

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[Mike McCauley]

Hi,

Can you send the rest of the GDB trace back?

Sounds a bit to me like you are using a non-GPIO peripheral.

Cheers.

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[Ron]

Mike,

I don't know how to do that but if you provide the direction I will.

Can give you this. Here is the code where the seg fault happens:
int ATU_0_PIN = RPI_BPLUS_GPIO_J8_37;
int ATU_1_PIN = RPI_BPLUS_GPIO_J8_35;



bcm2835_set_debug(0);
if(!bcm2835_init()) return 1;
bcm2835_gpio_fsel(ATU_0_PIN, BCM2835_GPIO_FSEL_INPT);

SEG FAULT -----> bcm2835_gpio_set_pud(ATU_0_PIN,
BCM2835_GPIO_PUD_DOWN); <- SEG FAULT

bcm2835_gpio_fsel(ATU_1_PIN, BCM2835_GPIO_FSEL_INPT);
bcm2835_gpio_set_pud(ATU_1_PIN, BCM2835_GPIO_PUD_UP);

73
Ron / W4MMP

[Mike McCauley]

Hello Ron,

well thats the problem.

The PUD is a different peripheral to the GPIO, and AFAICT, there is no access
to PUD without being root.

Cheers.

> >>>>> https://www.raspberrypi.org/blog/raspbian-jessie-> >>>>> is-> >>> here/

[Ron]

Hi David,

Ok, thanks much! I just thought I would give the application a spin
after upgrading to Raspbian/Jessie and your new version.

Back to root !

73
Ron / W4MMP

[Mike McCauley]

On Tuesday, March 01, 2016 12:23:56 AM 'Ron' via bcm2835 wrote:
> Hi David,
>
> Ok, thanks much! I just thought I would give the application a spin
> after upgrading to Raspbian/Jessie and your new version.
>
> Back to root !

Sorry bout that.

Nothing to be done though :-(

Cheers.