Possible Bug, or Possibly don't know what I'm doing.

[Bernhard Fischer]

On Fri, Feb 09, 2007 at 01:45:33PM -0600, Andy Kennedy wrote:
>Andy Kennedy wrote:
>> To restate my problem (in case some kind developer decides to help me):
>>
>> When I have the kernel command line parameter "console=ttyS0,115200n8" 
>> I get nice neat output on the serial line up until the init runs.  As 
>> soon as init runs, I get missing chars.  So, I replace the BusyBox 
>> init with minit, compiled from source and using the uCLibC gcc that I 
>> let buildroot make for me.  Same problem.  For some reason, when the 
>> system initializes -- after the kernel has reported all of its output, 
>> my serial console goes splat.  When I initialize the console using 
>> BusyBox (/sbin/getty -L ttyS0 115200 vt100) I get "X n", where X is 
>> {'i', 'g', 's', 'o', 'l', 'm'}, but I cannot find a pattern in it.  
>> One of these letters will appear each time I send enter.
>>
>> I have tried everything I can think of.  There is no script setting 
>> any of the line speeds -- in fact, I have even attempted to remove the 
>> scripts and still get the same thing.  Removing the 
>> console=ttyS0,115200n8 (or attempting any variant of it) has no 
>> affect, except without the console= I get no good output on the line.  
>> The only thing I haven't attempted yet is to replace the getty with an 
>> equivalent to see if that makes a difference.  I have also tried 9600, 
>> 38400, 19200, with E8, O8, 2 stop bits, and 1 stop bit in just about 
>> every combination, but I still cannot get a serial console.
>>
>> Can anyone offer a suggestion as to how I might fix this -- or some 
>> other place to start?
>>
>> Thanks in advance for any help you can offer,
>> Andy
>Okay, now I'm really confused.  Here is what I have done so far:
>Made my laptop boot with a console on ttyS0 and put a login shell on it 
>(to verify that I can do it -- I was beginning to think maybe I needed 
>to remove Linux from my computer and get rid of all of  it being to 
>stupid to own a computer, much less program an embedded system) and I 
>had no problems.  So, I took my syslinux disk and booted from it (the 
>SAME DISK THAT I'M USING TO BOOT THE EMBEDDED SYSTEM).  Not a problem, 
>everything comes up as you would expect.
>
>Given that this test worked there is one of about three possibilities:
>1) Cable issue.  Tested my serial cable on another embedded system (an 
>Arcom Viper), checks out.  Replaced the break-out cable from the 
>embedded system -- failed.  Tried a known good cable -- failed.  Tested 
>a different VersaLogic board -- failed.  Now, here is the part that 
>really yanked me around:
>
>The last time I booted the machine I didn't have the keyboard connected 
>to the break-out cable.  The boot went as it normally does except the 
>keyboard driver never reported a keyboard -- duh, it wasn't plugged in.  
>BusyBox init takes over the console and prints all kind of whack.  I 
>plug in the keyboard and the keyboard driver prints a perfect string 
>onto the serial console.
>
>I've looked through the code to see what type of initialization init is 
>doing to the console, but it doesn't look like it is re-initializing the 
>sucker at all.  The only thing that I can think is that BusyBox is doing 
>something that Linux doesn't do to interact with the ttyS0 so I'm not 
>getting what I expect.

IIRC busybox's init doesn't do anything special for serial lines.

As vda already suggested, better seek help on lkml or try to find
somebody to whom that <char><space><char>.. pattern sounds familiar.