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Date: Wed, 29 Jan 2020 13:56:56 -0800 (PST)
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Subject: Re: GNATCOLL-Mmap example
From: Bob Goddard <1963bib@googlemail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:57982
Date: 2020-01-29T13:56:56-08:00
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On Wednesday, 29 January 2020 08:19:11 UTC, Dmitry A. Kazakov  wrote:
[...]
> >>> 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
>              ...

Well... the call does not block, but I get spurious info back. It fires 1000 in around 1/4s, when it should be about 50Hz, that being the mains line frequency here.

On read, it should be reset. I tried making it RW, but the write fails.

Ho hum, that dent in the wall is getting bigger.


B