Re: Patch to support NACK packet from stub

[Andrew Cagney <ac131313@cygnus.com>]

"J.T. Conklin" wrote:
> 
> I discovered that the putpkt() routine does not handle NACK ('-')
> packets from remote stub, instead the NACK is junked and putpkt()
> waits until the subsequent read times out.  This is a big penalty
> (the default value of remote_timeout is 20 seconds) that can be
> easily avoided.
> 
> However, I had the '-' case fall through to SERIAL_TIMEOUT so the
> number of attempts a packet is sent is the same as timeouts.  If we
> wanted to add a remote_debug for the SERIAL_TIMEOUT case, that code
> needs to duplicated.

(Thanks for comments from Fernando Nasser and Michael Snyder)

I think it would be best if we leave this one out of 4.18 and have a
hard think about it for devo.  If you get rid of the timeout there is a
chance that other nastier things can happen.

Remembering that the remote GDB protocol is only robust against data
overrun what can happen is a sequence like:

-> <start><scrambled-data-looking-like-eop>
<- NACK
-> <more crambled data looking like another packet>
<- NACK

It is probably safer to just drain the target like the code is currently
doing.

	Andrew