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ARM/Thumb interworking problems

Jason Watton

I have a problem with calling ARM code from Thumb (C) code. The problem causes an 'undefined instruction' exception when using the 'switch' statement, because it is trying to call __ARM_switch8 from THUMB code like this:

0005b4  003b              MOVS     r3,r7
0005b6  f7ff fffe         BL       __ARM_switch8

Any suggestions? The address of __ARM_switch8 is even (0x10002cc4) and all THUMB code is at odd addresses, but the call to it is not being coded as a register-indirect call...

I have enabled ARM/Thumb interworking for this project.

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  • 0 in reply to Reinhard Keil

    Hi Reinhard,

    I am using the RealView compiler:

    IDE-Version:
    µVision3 V3.51
    Copyright (c) Keil Elektronik GmbH / Keil Software, Inc. 1995 - 2007

    License Information:
    XXX

    Tool Version Numbers:
    Toolchain Path: I:\Keil\ARM\BIN30\
    C Compiler: ARMCC.Exe V3.0.0.951
    Assembler: ARMASM.Exe V3.0.0.951
    Linker/Locator: ARMLINK.Exe V3.0.0.951
    Librarian: ARMAR.Exe V3.0.0.951
    Hex Converter: FROMELF.Exe V3.0.0.951
    CPU DLL: SARM.DLL V3.05
    Dialog DLL: DARMATS9.DLL
    Target DLL: BIN\UL2ARM.DLL V1.26b
    Dialog DLL: TARMATS9.DLL V1.00

    Code sample:

    do
{
        char *pMs       g;
        TestKey = GetCh();
        switch (TestKey)
        {
        case KEY_0:
                pMsg = "0      ";
                break;
        case KEY_1:
                pMsg = "1      ";
                break;
        ...
        }
        GotoXY(6, 1);               // display the key press's description
        Puts(pMsg);
} while (TestKey != KEY_CANCEL);

    This compiles to:

    ;;;506                             do
0003c2  46c0              MOV      r8,r8
;;;507                                  {
;;;508                                          char *pMsg;
;;;509
;;;510                                          TestKey = GetCh();
                  |L1.964|
0003c4  f7ff fffe         BL       GetCh
0003c8  0007              MOVS     r7,r0
;;;511                                          switch (TestKey)
0003ca  e0f3              B        |L1.1460|
...
                  |L1.1460|
0005b4  003b              MOVS     r3,r7
0005b6  f7ff fffe         BL       __ARM_switch8
0005ba  0e1a              DCB      0x1a,0x0e
0005bc  1411              DCB      0x11,0x14
0005be  1a17              DCB      0x17,0x1a
...
;;;512                                          {
;;;513                                          case KEY_0:
;;;514                                                  pMsg = "0      ";
0005d6  a07e              ADR      r0,|L1.2000|
0005d8  9000              STR      r0,[sp,#0]
;;;515                                                  break;
0005da  e045              B        |L1.1640|
;;;516                                          case KEY_1:
;;;517                                                  pMsg = "1      ";
0005dc  a07e              ADR      r0,|L1.2008|
0005de  9000              STR      r0,[sp,#0]
;;;518                                                  break;
0005e0  e042              B        |L1.1640|
...
                  |L1.1640|
000668  46c0              MOV      r8,r8                 ;515
;;;582                                          }
;;;583                                          GotoXY(6, 1);               // display the key press's description
00066a  2101              MOVS     r1,#1
00066c  2006              MOVS     r0,#6
00066e  f7ff fffe         BL       GotoXY
;;;584                                          Puts(pMsg);
000672  9800              LDR      r0,[sp,#0]
000674  f7ff fffe         BL       Puts
;;;585                                  } while (TestKey != KEY_CANCEL);
000678  2f0a              CMP      r7,#0xa
00067a  d000              BEQ      |L1.1662|
00067c  e6a2              B        |L1.964|
;;;586                                  SetShiftLock(FALSE); // Makes using the unit difficult if it's left on
                  |L1.1662|
...

    My problem is the C 'switch' statement itself which is being handled by an (ARM-coded) function __ARM_switch8 which is being called using 'BL': the processor (Atmel AT91RM9200) isn't switching into ARM mode and the result is an 'undefined instruction' exception.

    Thanks,

    Jason.

  • 0 in reply to Jason Watton

    we need to duplicate this issue. Please send a test case to support.intl@keil.com.

  • 0 in reply to Reinhard Keil

    Thanks, Reinhard - I have submitted a Test Case.

    Jason.