[U-Boot-Users] Loads function and flow control.

Wolfgang Denk wd at denx.de
Mon May 26 17:34:08 CEST 2003

In message <20030526150145.GO24207 at pengutronix.de> you wrote:
> On Mon, May 26, 2003 at 04:46:05PM +0200, Wolfgang Denk wrote:

[about flow control]

> > No there is none, and there is no need for one.
> ... as the kermit protocol ensures that packets with incorrect checksums
> are resent. 

Flow control and checksums address two different kinds  of  problems.
While  checksumming  can detect the effects of overrun problems, flow
control cannot solve the  other  problems  that  can  cause  checksum

So far, in all cases I have seen  with  U-Boot  (including  the  pre-
decessor  projects  PPCBoot and ARMBoot) the CPUs were fast enought o
easily handle serial downloads using  both  "loadb"  and  "loads"  at
least at 115200 bps. Without any need for flow control.

> > I don't think so. Even at high baud rates (like 115200 bps) there  is
> > more than enough time to receive characters through the serial line -
> > remember  that  U-Boot  is  strictly  single-tasking,  so the CPU has
> > nothing better to do but to wait for characters.
> Nevertheless there may be situations where for example cables make
> problems, so using a mechanism which checks if the data is correct is
> not the worst idea. 

But this has nothing to do with flow control.

You are right, a protocol with  error  checking  and  recovery  (like
kermit  binary  protocol)  _is_  superior to a protocol without or no
protocol at all - but this was not the topic here.

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
If you can't beat it or corrupt it, you pretend it was your  idea  in
the first place.                 - Terry Pratchett, _Guards! Guards!_

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