Forum: ARM programming with GCC/GNU tools Problem with C++ ISR (using WINARM)

Author: Sameer Patil (sameer_pat)
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        Firstly , i am a new to G++....so pls help me from that point of
view.....i have a C++ code written and i am using RTC interrupt.....sm
part of the code troubles if system has an interrupt.....the code
particularly troubles when accessing "some" Global Objects.....here is
how my startup file looks....i have just picked it up from one of the
examples in winarm....Please suggest if any changes have to be done
either to the startup file or any other change......My ISR only sets a
flag (unsigned char variable to TRUE)and so no "heavy code " goes in
my start up file......

        .global main                    // int main(void)

        .global _etext                  // -> .data initial values in
        .global _data                   // -> .data area in RAM
        .global _edata                  // end of .data area
        .global __bss_start             // -> .bss area in RAM
        .global _bss_end_             // end of .bss area
        .global _stack                  // top of stack

// Stack Sizes
        .set  UND_STACK_SIZE, 0x00000004
        .set  ABT_STACK_SIZE, 0x00000004
        .set  FIQ_STACK_SIZE, 0x00000004
        .set  IRQ_STACK_SIZE, 0X00000080
        .set  SVC_STACK_SIZE, 0x00000004

// Standard definitions of Mode bits and Interrupt (I & F) flags in PSRs
        .set  MODE_USR, 0x10            // User Mode
        .set  MODE_FIQ, 0x11            // FIQ Mode
        .set  MODE_IRQ, 0x12            // IRQ Mode
        .set  MODE_SVC, 0x13            // Supervisor Mode
        .set  MODE_ABT, 0x17            // Abort Mode
        .set  MODE_UND, 0x1B            // Undefined Mode
        .set  MODE_SYS, 0x1F            // System Mode

        .equ  I_BIT, 0x80               // when I bit is set, IRQ is
        .equ  F_BIT, 0x40               // when F bit is set, FIQ is

        .code 32
        .align 2

        .global _boot
        .func   _boot

// Runtime Interrupt Vectors
// -------------------------
        b     _start                    // reset - _start
        ldr   pc,_undf                  // undefined - _undf
        ldr   pc,_swi                   // SWI - _swi
        ldr   pc,_pabt                  // program abort - _pabt
        ldr   pc,_dabt                  // data abort - _dabt
        nop                             // reserved
        ldr   pc,[pc,#-0xFF0]           // IRQ - read the VIC
        ldr   pc,_fiq                   // FIQ - _fiq

#if 0
// Use this group for production
_undf:  .word _reset                    // undefined - _reset
_swi:   .word _reset                    // SWI - _reset
_pabt:  .word _reset                    // program abort - _reset
_dabt:  .word _reset                    // data abort - _reset
_irq:   .word _reset                    // IRQ - _reset
_fiq:   .word _reset                    // FIQ - _reset

// Use this group for development
_undf:  .word __undf                    // undefined
_swi:   .word __swi                     // SWI
_pabt:  .word __pabt                    // program abort
_dabt:  .word __dabt                    // data abort
_irq:   .word __irq                     // IRQ
_fiq:   .word __fiq                     // FIQ

__undf: b     .                         // undefined
__swi:  b     .                         // SWI
__pabt: b     .                         // program abort
__dabt: b     .                         // data abort
__irq:  b     .                         // IRQ
__fiq:  b     .                         // FIQ
        .size _boot, . - _boot

// Setup the operating mode & stack.
// ---------------------------------
        .global _start, start, _mainCRTStartup
        .func   _start


// Initialize Interrupt System
// - Set stack location for each mode
// - Leave in System Mode with Interrupts Disabled
// -----------------------------------------------
        ldr   r0,=_stack
        msr   CPSR_c,#MODE_UND|I_BIT|F_BIT // Undefined Instruction Mode
        mov   sp,r0
        sub   r0,r0,#UND_STACK_SIZE
        msr   CPSR_c,#MODE_ABT|I_BIT|F_BIT // Abort Mode
        mov   sp,r0
        sub   r0,r0,#ABT_STACK_SIZE
        msr   CPSR_c,#MODE_FIQ|I_BIT|F_BIT // FIQ Mode
        mov   sp,r0
        sub   r0,r0,#FIQ_STACK_SIZE
        msr   CPSR_c,#MODE_IRQ|I_BIT|F_BIT // IRQ Mode
        mov   sp,r0
        sub   r0,r0,#IRQ_STACK_SIZE
        msr   CPSR_c,#MODE_SVC|I_BIT|F_BIT // Supervisor Mode
        mov   sp,r0
        sub   r0,r0,#SVC_STACK_SIZE
        msr   CPSR_c,#MODE_SYS|I_BIT|F_BIT // System Mode
        mov   sp,r0

// Copy initialized data to its execution address in RAM
// -----------------------------------------------------
#ifdef ROM_RUN
        ldr   r1,=_etext                // -> ROM data start
        ldr   r2,=_data                 // -> data start
        ldr   r3,=_edata                // -> end of data
1:      cmp   r2,r3                     // check if data to move
        ldrlo r0,[r1],#4                // copy it
        strlo r0,[r2],#4
        blo   1b                        // loop until done
// Clear .bss
// ----------
        mov   r0,#0                     // get a zero
        ldr   r1,=__bss_start           // -> bss start
        ldr   r2,=__bss_end__           // -> bss end
2:      cmp   r1,r2                     // check if data to clear
        strlo r0,[r1],#4                // clear 4 bytes
        blo   2b                        // loop until done

   Call C++ constructors (for objects in "global scope")
   ctor loop added by Martin Thomas 4/2005
   based on a Anglia Design example-application for ST ARM

    LDR   r0, =__ctors_start__
    LDR   r1, =__ctors_end__
    CMP   r0, r1
    BEQ   ctor_end
    LDR   r2, [r0], #4
    STMFD   sp!, {r0-r1}
    MOV   lr, pc
    MOV   pc, r2
    LDMFD   sp!, {r0-r1}
    B     ctor_loop

// Call main program: main(0)
// --------------------------
        mov   r0,#0                     // no arguments (argc = 0)
        mov   r1,r0
        mov   r2,r0
        mov   fp,r0                     // null frame pointer
        mov   r7,r0                     // null frame pointer for thumb
        ldr   r10,=main
        mov   lr,pc
        bx    r10                       // enter main()

/* "global object"-dtors are never called and it should not be
   needed since there is no OS to exit to. */

        .size   _start, . - _start

        .global _reset, reset, exit, abort
        .func   _reset
#if 0
// Disable interrupts, then force a hardware reset by driving P23 low
// -------------------------------------------------------------------
        mrs   r0,cpsr                   // get PSR
        orr   r0,r0,#I_BIT|F_BIT        // disable IRQ and FIQ
        msr   cpsr,r0                   // set up status register

        ldr   r1,=(PS_BASE)             // PS Base Address
        ldr   r0,=(PS_PIO)              // PIO Module
        str   r0,[r1,#PS_PCER_OFF]      // enable its clock
        ldr   r1,=(PIO_BASE)            // PIO Base Address
        ldr   r0,=(1<<23)               // P23
        str   r0,[r1,#PIO_PER_OFF]      // make sure pin is contolled by
        str   r0,[r1,#PIO_CODR_OFF]     // set the pin low
        str   r0,[r1,#PIO_OER_OFF]      // make it an output
        b     .                         // loop until reset

        .size _reset, . - _reset


Author: Clifford Slocombe (clifford)
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You have not really explained your problem, or how it relates to C++, or
the ISR (you only posted assembler!). You have only posted the startup
code, what makes you think the problem is there, all the issues you
mentioned appear to be related to code you have not posted. What can we

If using global objects, then the startup must invoke the constructors
for those (and any static objects). Your start up does that.

The order in which global objects are are constructed is undefined, so
each one must be self contained and not depend on any other being

If a global object is accessed in the ISR, any access to that global
must either be atomic, or uninterruptable.

Also any variables shared between the interrupt and normal context or
between separate threads must be declared volatile.



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