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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: GNATCOLL-Mmap example
Date: Wed, 29 Jan 2020 09:19:08 +0100
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Date: 2020-01-29T09:19:08+01:00
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On 2020-01-28 21:17, Bob Goddard wrote:
> On Tuesday, 28 January 2020 20:07:56 UTC, Dmitry A. Kazakov  wrote:
>> On 2020-01-28 19:53, Bob Goddard wrote:
>>> On Tuesday, 28 January 2020 08:25:25 UTC, Dmitry A. Kazakov  wrote:
>>>> On 2020-01-25 22:52, Bob Goddard wrote:
>>>>
>>>>> I need to map the RPi's GPIO memory addresses so that I can do what I need to do.
>>>>
>>>> See files under:
>>>>
>>>>       /sys/class/gpio
>>>>
>>>> You can use standard Ada I/O to read and set GPIO pins. E.g.
>>>>
>>>>       /sys/class/gpio/gpio/XXX/value
>>>
>>> This was the way I started, but could not get it to read anything. It just blocks trying to read a single character. My c code works fine using the wiringPi libs.
>>
>> If I correctly remember you should rewind the file after each reading.
> 
> It did not get that far. It blocks right at the start.

What about this

       use GNAT.OS_Lib;

       FD     : File_Descriptor;
       Buffer : aliased char;
    begin
       FD := Open_Read ("/sys/class/gpio/gpio/XXX/value", Binary);
       Lseek (FD, 0, Seek_Set);
       if 1 = Read (FD, Buffer'Address, 1) then
          if Buffer = '1' then
             ...

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de