RE: [avr-libc-dev] Inline assembler and compiler optimization

[Weddington, Eric]

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of Joerg Wunsch
> Sent: Monday, March 23, 2009 1:41 PM
> To: address@hidden
> Subject: Re: [avr-libc-dev] Inline assembler and compiler optimization
> 
> As Weddington, Eric wrote:
> 
> > If we do that, we might as well make it a public symbol, yes?:
> > #define memory_barrier()  __asm__ __volatile__(""::"memory")
> 
> I hesitate to add stuff like that to existing header files.
> memory_barrier belongs into the application namespace, so existing
> applications could legitimately already use that name (and are likely
> doing it in case they really need the functionality).
> 
> Would you like _MEMORY_BARRIER() more?  That's in the implementation
> namespace.

Let's see if something is available to us in the builtins.


> Likewise, the same goes for using nop(), as tempting as it is.  Again,
> _NOP() would be fine, as will __nop().

Hmm. I think that might be included as part of the new builtins for the AVR 
port.


> Another definition that just came to mind: setting the JTD bit, a
> timed sequence.  See here:
> 
> http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopi
> c&p=553919#553836
> 
> for a sample implementation.  I wouldn't see any of the existing
> header files where that really fits.  (It needs to be polished up, I
> think some controllers use MCUCR, and some use MCUCSR for JTD.)

We definitely need to create an API for this, and all other timed sequences. 
There are a number of timed sequences in the xmega chips that need to be added.

I know you don't care too much about xmega, because of inability to program it 
with avrdude. But a visual inspection of the resulting code from an inline 
assembly macro would be good enough for me.


> If we decide for a new header file, how to name it?  <avr/asm.h>?
> <avr/misc.h>?

I don't like misc as it is too vague.

For the JTD timed sequence, why not a new <avr/jtag.h> file? It doesn't matter 
to me that it may only have one macro in it. At least it would be easy to 
remember.

Eric