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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Duration for GNAT on ARM
Date: Tue, 23 Dec 2014 23:42:51 +0100
Organization: cbb software GmbH
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Date: 2014-12-23T23:42:51+01:00
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On Tue, 23 Dec 2014 21:21:57 +0000, Simon Wright wrote:

> You use -gnatS to get GNAT to output a representation of package
> Standard.
> 
> If you do this with a native compiler, you get (typically)
> 
>    type Duration is delta 0.000000001
>      range -((2 ** 63 - 1) * 0.000000001) ..
>            +((2 ** 63 - 1) * 0.000000001);
>    for Duration'Small use 0.000000001;
> 
> However, if I do this with both GNAT GPL 2014 and FSF GCC 4.9.1
> cross-compiling to arm-eabi for the STM32F4 family (Cortex M4), I get
> 
>    type Duration is delta 0.020
>      range -((2 ** 31 - 1) * 0.020) ..
>            +((2 ** 31 - 1) * 0.020);
>    for Duration'Small use 0.020;
> 
> I can understand the 32-bit vs 64-bit part - a misguided attempt at
> efficiency, perhaps - but who gets to say that the clock runs at 50 Hz?

E.g. those who have time source derived from timer interrupts.

> On the STM32's with STMicroelectronics' HAL, the tick is 1 kHz.

But does the RTL assumed by the compiler use this clock?

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