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IDProjectCategoryView StatusLast Update
0037914FPCCompilerpublic2020-10-12 21:59
ReporterChristo Crause Assigned ToFlorian  
Status closedResolutionfixed 
Product Version3.3.1 
Fixed in Version3.3.1 
Summary0037914: AVR [patch] Sometimes registers r0 or r1 are pushed for avrtiny
DescriptionWhen calling a function from an interrupt handler the compiler sometimes insert push/pop instructions for r0 & r1, obviously leading to assembler errors. The code below is an example which triggers this problem.

This problem can be fixed by removing r0, r1 from the volatile register set, see attached patch.
Steps To ReproduceCompile test program with
~/fpc/3.3.1/compiler/ppcrossavr -n @~/fpc/3.3.1/fpc.cfg -Wpattiny10 test.lpr

program test;

function Sound1(t: uint32): byte;

  t: uint32;

procedure genSound; alias: 'TIM0_OVF_ISR'; interrupt;
  OCR0A := Sound1(t);

Additional InformationCompiler/assembler output:
Free Pascal Compiler version 3.3.1 [2020/10/06] for avr
Copyright (c) 1993-2020 by Florian Klaempfl and others
Target OS: Embedded
Compiling test.lpr
test.lpr(3,10) Warning: Function result does not seem to be set
test.lpr(8,3) Warning: Variable "t" read but nowhere assigned
Assembling test
test.s: Assembler messages:
test.s:70: Error: register name or number from 16 to 31 required
test.s:71: Error: register name or number from 16 to 31 required
test.s:87: Error: register name or number from 16 to 31 required
test.s:88: Error: register name or number from 16 to 31 required
test.lpr(19) Error: Error while assembling exitcode 1
test.lpr(19) Fatal: There were 2 errors compiling module, stopping
Fatal: Compilation aborted
TagsNo tags attached.
Fixed in Revision47102
Attached Files


Christo Crause

2020-10-12 21:37


cpupara.patch (584 bytes)   
diff --git a/compiler/avr/cpupara.pas b/compiler/avr/cpupara.pas
index 0c4289e68a..1567fddc30 100644
--- a/compiler/avr/cpupara.pas
+++ b/compiler/avr/cpupara.pas
@@ -58,7 +58,7 @@ unit cpupara;
     function tcpuparamanager.get_volatile_registers_int(calloption : tproccalloption):tcpuregisterset;
         if CPUAVR_16_REGS in cpu_capabilities[current_settings.cputype] then
-          result:=VOLATILE_INTREGISTERS-[RS_R18,RS_R19]
+          result:=VOLATILE_INTREGISTERS-[RS_R0,RS_R1,RS_R18,RS_R19]
cpupara.patch (584 bytes)   


2020-10-12 21:44

administrator   ~0126268

Thanks, applied.

Christo Crause

2020-10-12 21:59

reporter   ~0126270

7 Minutes, this is probably some kind of record! Thanks Florian.

Issue History

Date Modified Username Field Change
2020-10-12 21:37 Christo Crause New Issue
2020-10-12 21:37 Christo Crause File Added: cpupara.patch
2020-10-12 21:44 Florian Assigned To => Florian
2020-10-12 21:44 Florian Status new => resolved
2020-10-12 21:44 Florian Resolution open => fixed
2020-10-12 21:44 Florian Fixed in Version => 3.3.1
2020-10-12 21:44 Florian Fixed in Revision => 47102
2020-10-12 21:44 Florian FPCTarget => -
2020-10-12 21:44 Florian Note Added: 0126268
2020-10-12 21:59 Christo Crause Status resolved => closed
2020-10-12 21:59 Christo Crause Note Added: 0126270