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Re: How do serial port device drivers interact with COMMS drivers?


Patrick Doyle wrote:
> 
> As I am trying to increase my understanding and appreciation of eCos, I have
> recently started to wonder about this.  For the two cases I looked at (the
> QUICC serial device drivers and the PC), it appears that there are no
> mechanisms to avoid conflicts between using the serial port via the device
> driver interface and using the serial port via the COMMS interface.  Did I
> miss something?  If I open "/dev/ser1" and change the baud rate to, say
> 9600, won't that interfere terribly with my debugger session, which happens
> to be using serial port 1 at 38,400 baud?

Yes, welcome to the embedded world where we don't stop you playing with the
hardware :-).

> It occurs to me that this is not an issue because folks who use the serial
> port device drivers do so because they happen to know exactly what is hooked
> up to which serial port for a given embedded application.   Therefore, they
> would never write code that opened "/dev/ser1" because they know that that
> is what they use for the debugger.  Is this the case?  Or, did I miss
> something somewhere?

Well, there's also the problem of determining whether it's deliberate or
accidental. I've certainly switched from GDB stubs to serial dd's when
debugging the serial dd's on a board with only 1 serial port.
 
> On a related note, it seems to me that a boot monitor (with the Virtual
> Vector support enabled) will support two communication interfaces.  One for
> "console" I/O and one for "debug I/O" (such as a GDB style debugger).  If I
> wanted to use any other I/O interfaces, I should do so using the device
> driver paradigm (which, presumably is interrupt driven and, therefore, more
> friendly to multitasking).  Is my understanding correct?

Yes.

Jifl
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