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Re: arm-gcc: avoid calling other system functions

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Il 18/05/2018 09:51, David Brown ha scritto:
> On 18/05/18 09:07, pozz wrote:
>> Il 17/05/2018 17:06, David Brown ha scritto:
>>> On 17/05/18 14:37, pozz wrote:
>>>> I'm trying to put all ISRs in RAM[*]. Unfortunately, depending on the
>>>> code, arm-gcc could call some system functions that are located in
>>>> Flash.
>>>>
>>>> For example, if I use a switch statement, the compiler calls a piece
>>>> of code of system libraries (that are in Flash) that use a table
>>>> lookup to manage the switch.
>>>>
>>>> Is it possible to force arm-gcc to avoid calling system functions
>>>> from ISRs, so it can be executed completely in RAM?
>>>
>>> There is, AFAIK, no way to force this.  It is not normally a problem
>>> as ISRs should generally be as short and fast as possible.
>>
>> I always try to keep the ISR short, simple and fast.  However a simple
>> switch statement (a different way to write a sequence of if statements)
>> is compiled in assembler code that uses "libgcc functions".
> 
> Can you give an small example here?  That sounds very strange.  gcc can
> use a variety of tactics for switch statements, including jump tables,
> calculated jumps, sequences of conditional tests, and binary trees of
> conditional tests - and combinations of these.  But I can't think of any
> situation where it would use a language support function (at least, not
> on an ARM).

Read this:
https://www.freertos.org/FreeRTOS_Support_Forum_Archive/April_2016/freertos_Use_of_switch_case_in_FreeRTOS_code_a821b79ej.html

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arm-gcc: avoid calling other system functions pozz <pozzugno@gmail.com> - 2018-05-17 14:37 +0200
  Re: arm-gcc: avoid calling other system functions Grant Edwards <invalid@invalid.invalid> - 2018-05-17 13:27 +0000
    Re: arm-gcc: avoid calling other system functions pozz <pozzugno@gmail.com> - 2018-05-17 15:35 +0200
      Re: arm-gcc: avoid calling other system functions Grant Edwards <invalid@invalid.invalid> - 2018-05-17 14:18 +0000
        Re: arm-gcc: avoid calling other system functions David Brown <david.brown@hesbynett.no> - 2018-05-17 17:08 +0200
        Re: arm-gcc: avoid calling other system functions pozz <pozzugno@gmail.com> - 2018-05-18 08:47 +0200
  Re: arm-gcc: avoid calling other system functions pozz <pozzugno@gmail.com> - 2018-05-17 15:30 +0200
  Re: arm-gcc: avoid calling other system functions David Brown <david.brown@hesbynett.no> - 2018-05-17 17:06 +0200
    Re: arm-gcc: avoid calling other system functions pozz <pozzugno@gmail.com> - 2018-05-18 09:07 +0200
      Re: arm-gcc: avoid calling other system functions David Brown <david.brown@hesbynett.no> - 2018-05-18 09:51 +0200
        Re: arm-gcc: avoid calling other system functions pozz <pozzugno@gmail.com> - 2018-05-21 09:14 +0200
          Re: arm-gcc: avoid calling other system functions David Brown <david.brown@hesbynett.no> - 2018-05-21 12:50 +0200
        Re: arm-gcc: avoid calling other system functions Joe Chisolm <jchisolm6@earthlink.net> - 2018-05-21 10:15 -0500
          Re: arm-gcc: avoid calling other system functions David Brown <david.brown@hesbynett.no> - 2018-05-21 19:31 +0200
            Re: arm-gcc: avoid calling other system functions pozz <pozzugno@gmail.com> - 2018-05-22 09:05 +0200
              Re: arm-gcc: avoid calling other system functions David Brown <david.brown@hesbynett.no> - 2018-05-22 10:59 +0200
              Re: arm-gcc: avoid calling other system functions Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-05-22 15:24 +0300
                Re: arm-gcc: avoid calling other system functions pozz <pozzugno@gmail.com> - 2018-05-22 14:55 +0200
  Re: arm-gcc: avoid calling other system functions Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-05-18 12:41 +0300

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