Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.arch.embedded > #27767

Re: arm-gcc: avoid calling other system functions

Show all headers | View raw

On 21/05/18 09:14, pozz wrote:
> 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 
> 

That refreshes my memory!  But I didn't get an example then, and haven't 
got one now.  What sort of switch situations are you seeing calls to 
language support functions?

Back to comp.arch.embedded | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

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

csiph-web