[U-Boot] common/xyzmodem.c, ymodem, slow behavior receiving bytes

[Wolfgang Denk <wd@denx.de>]

Dear Angelo Dureghello,

please don't top-post / full quote.

In message <20121113001651.GA21177@angel3> you wrote:
> 
> seems that mcf5307, working at 90Mhz, is not fast enough when "-Os -g" 
> compile options are set.
> 
> I changed for test config.mk from
> 
> DBGFLAGS= -g # -DDEBUG
> OPTFLAGS= -Os #-fomit-frame-pointer
> 
> into
> 
> DBGFLAGS= #-g # -DDEBUG
> OPTFLAGS= -O2 #-Os #-fomit-frame-pointer
> 
> common compiles now with -O2 and ymodem works fine again at 115200.

Removing -g makes no sense in this cotext.  It has no impact on the
generated code.

I am really surprised about your claim that the -O2 compiled code is
actually running faster than the -Os compiled one on a low-end system
as yours (90 MHz CPU clock, 8 kB cache size).

Which exact tool chain are you using to build the code?

> Also, i don't understand why "-g" is set by default. 

It is set because it is useful to some (those in the need of debugging
their code) and does not hurt others.

> Is there a way to override/customize this options for this cpu ?

I am not convinced that it makes sense to change settings on a per-cpu
base.  A 90 MHz CPU should be more than sufficient to receive data at
115kbps.  I can only compare against 50 MHz PowerQuicc I systems
(which is about the lowest end machines I have at hands now), and
there no such problem exists.

It would be good to understand exactly where the problem is coming
from.  I don't think that the -Os setting is the core of the problem;
I tend to suspect rather your tool chain or your serial driver or such.

> Or i have to definitely step down to 57600 ?

There should be no need for that.

Best regards,

Wolfgang Denk

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