[Bug 1001466] /dev/null serial driver

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--- Comment #5 from Sergei Gavrikov <sergei.gavrikov@gmail.com> 2012-02-16 12:20:05 GMT ---
(In reply to comment #4)

[snip]

> Well the name '/dev/null' is known for decades and for any *nix
> developer this name tells what it does, as posix/opengroup use this
> name.

But it is not terminal/teletype/console/serial, etc. From your source
(Open Group)

  /dev/null
    An infinite data source and data sink. Data written to /dev/null
    shall be discarded. Reads from /dev/null shall always return
    end-of-file (EOF).

(EOF) - END OF *FILE*. As I said /dev/null is a special FILE. But,
/dev/null is not TTY device (not terminal):

Check in Python

  >>> import os
  >>> fd=os.open("/dev/null", os.O_RDWR)
  >>> os.isatty(fd)
  False

Check in C

  % cc -xc - <<EOF
  > main(){printf("/dev/null is %s
tty\n",isatty(open("/dev/null","r"))?"a":"not");}
  EOF
  % ./a.out
  /dev/null is not tty

[snip]

> AFAIK there is no specific requirements regarding the implementation,
> only the name and the result it must provide. Using the serial
> abstraction seemed fine to me since most often /dev/null is used to
> sink data coming from a byte stream. I suppose that serial devices are
> embedded in all targets, at least for diag_printf(), that why I placed
> it here so there is no need to bring other components.

If your concern is diagnostic output only (diag_printf()), you ain't
gonna need it. I mean /dev/null. The eCos diagnostic routines do not use
devfs. Look

   infra/current/src/diag.cxx:93

HAL_DIAG_WRITE_CHAR() macro is defined in hal_diag.h as

#define HAL_DIAG_WRITE_CHAR(_c_) hal_if_diag_write_char(_c_)

Further

  hal/common/current/src/hal_if.c

Using CYGACC_CALL_IF_* macros you can (re-)assign diagnostic channel
anywhere, for example, to some auxiliary COMM channel (black-hole).
Excellent example how to to deal with eCos COMM channels is RedBoot

  redboot/current/src/main.c
  redboot/current/src/io.c

Look around mon_write_char() there. So, (IMHO) in the simplest case you
would just use diag_init_putc() to solve your issue.

More on eCos VV & COMMS channels

  http://ecos.sourceware.org/docs-latest/ref/hal-porting-guide.html
  http://ecos.sourceware.org/docs-latest/ref/hal-calling-if.html

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