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Re: [avr-gcc-list] avr-gcc and C++ ?

From: Arreckx
Subject: Re: [avr-gcc-list] avr-gcc and C++ ?
Date: Tue, 3 Apr 2001 19:00:11 +0100

I am currently working on the C++ support for the AVR.
Indeed, the SRAM is limited (unless you add external RAM), but careful C++
design can be very efficient.

I have built the avr-g++ successfully (Windows and Linux) and I can compile
C++ files. I used the source from http://www.combio.de/avr/ to which I added
the g++ branch. I use cygwin to build in Windows, and everything works out
of the box.

What is good is that this compiler is the latest gcc and is very close to
the standard, and since Avr uses ELF format (rather than COFF), templates
and inline are dealt with in style. Rtti and exceptions are missing. But
this is a good thing. Gcc exceptions are enormous and C++ exception should
never be used on small and average size embedded system. Rtti will stop
developer from using dynamic cast, and probably multiple inheritance,
another good thing !

Unfortunately, I haven't manage to build the stdlibc++. This library is need
for a lot of the built-in C++ stuff, like calling constructors of global or
static object instances etc... configure is failing.
I don't think the stdlibc++ is right for the AVR anyway.
So what was done for libc will have to be done for libstdc++. I am looking
for buddies to help me with this task.

To prove what I was saying, here is the standard waggle test I always do on
a new target to check it is alive, but in C++.

#include <inttypes.h>
#include <io.h>

class waggle
// Construction
   explicit waggle( uint8_t port )  : _port(port) {}

// Data members
   uint8_t _port;
   // Accessor
   uint8_t getPort() const
      { return _port; }

// Operation
   void start( const uint8_t bit ) const;

void waggle::start( const uint8_t bit ) const
   for (;;)
      __mmio((_port)) |= BV((bit));
      __mmio((_port)) &= ~BV((bit));

static const uint8_t port = PORTC;

int main()
   waggle Waggler( port );

   Waggler.start( 4 );

   return 0;

and the corresponding assembly it generates :

Disassembly of section .text:

00000000 <main>:
   0:   ce ef           ldi     r28, 0xFE       ; 254
   2:   df e0           ldi     r29, 0x0F       ; 15
   4:   de bf           out     0x3e, r29       ; 62
   6:   cd bf           out     0x3d, r28       ; 61
   8:   25 e1           ldi     r18, 0x15       ; 21
   a:   29 83           std     Y+1, r18        ; 0x01
   c:   60 e0           ldi     r22, 0x00       ; 0
   e:   8c 2f           mov     r24, r28
  10:   9d 2f           mov     r25, r29
  12:   01 96           adiw    r24, 0x01       ; 1
  14:   03 d0           rcall   .+6             ; 0x1c
  16:   80 e0           ldi     r24, 0x00       ; 0
  18:   90 e0           ldi     r25, 0x00       ; 0

0000001a <__stop_progIi__>:
  1a:   ff cf           rjmp    .-2             ; 0x1a

0000001c <waggle::start(unsigned char) const>:
  1c:   b9 2f           mov     r27, r25
  1e:   a8 2f           mov     r26, r24
  20:   46 2f           mov     r20, r22
  22:   21 e0           ldi     r18, 0x01       ; 1
  24:   30 e0           ldi     r19, 0x00       ; 0
  26:   02 c0           rjmp    .+4             ; 0x2c
  28:   22 0f           add     r18, r18
  2a:   33 1f           adc     r19, r19
  2c:   4a 95           dec     r20
  2e:   e2 f7           brpl    .-8             ; 0x28
  30:   92 2f           mov     r25, r18
  32:   90 95           com     r25
  34:   6c 91           ld      r22, X
  36:   e6 2f           mov     r30, r22
  38:   ff 27           eor     r31, r31
  3a:   50 a1           ldd     r21, Z+32       ; 0x20
  3c:   52 2b           or      r21, r18
  3e:   50 a3           std     Z+32, r21       ; 0x20
  40:   4c 91           ld      r20, X
  42:   e4 2f           mov     r30, r20
  44:   ff 27           eor     r31, r31
  46:   30 a1           ldd     r19, Z+32       ; 0x20
  48:   39 23           and     r19, r25
  4a:   30 a3           std     Z+32, r19       ; 0x20
  4c:   f3 cf           rjmp    .-26            ; 0x34
  4e:   08 95           ret
Disassembly of section .data:


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