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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Duration for GNAT on ARM
Date: Tue, 23 Dec 2014 21:21:57 +0000
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Date: 2014-12-23T21:21:57+00:00
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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?
On the STM32's with STMicroelectronics' HAL, the tick is 1 kHz.