SERIAL_CONSOLE versus SERIAL_CONSOLES?

SERIAL_CONSOLE versus SERIAL_CONSOLES?

[Robert P. J. Day]

  i am well aware that if one wants to define a single serial console,
then using the SERIAL_CONSOLE variable will work just fine, as in:

SERIAL_CONSOLE ?= "115200 ttyS0"

and if you want to define multiple possible consoles, use:

SERIAL_CONSOLES = "115200;ttyAMA0 115200;ttyAMA1"

  however, i just noticed in the default bitbake.conf:

SERIAL_CONSOLE ??= ""
SERIAL_CONSOLES ??= "${@d.getVar('SERIAL_CONSOLE', True).replace(' ', ';')}"

where SERIAL_CONSOLES is defined in terms of SERIAL_CONSOLE, which
suggests to me that, really, it's SERIAL_CONSOLES that will be used
for further configuration, is that right?

  for instance, i see in
meta/recipes-core/systemd/systemd-serialgetty.bb, the test:

  do_install() {
        if [ ! -z "${SERIAL_CONSOLES}" ] ; then
                default_baudrate=`echo "${SERIAL_CONSOLES}" | sed 's/\;.*//'

wherein, once upon a time, i would have thought, "hey, i'm not
assigning anything to SERIAL_CONSOLES so that doesn't apply to me."
when, of course, it *does* apply now that i read things properly.

  so is it a fair statement that, pedantically, i might as well just
define everything in terms of SERIAL_CONSOLES and think that way?

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================

Re: SERIAL_CONSOLE versus SERIAL_CONSOLES?

[Phil Blundell]

On Mon, 2016-10-17 at 07:57 -0400, Robert P. J. Day wrote:
> 
  so is it a fair statement that, pedantically, i might as well just
> define everything in terms of SERIAL_CONSOLES and think that way?
> 

Yes.  SERIAL_CONSOLE predates SERIAL_CONSOLES and remains supported in
the configuration for backwards compatibility.  New configurations and
recipes should probably use SERIAL_CONSOLES and ignore SERIAL_CONSOLE
entirely.

p.

Re: SERIAL_CONSOLE versus SERIAL_CONSOLES?

[Robert P. J. Day]

[-- Attachment #1: Type: text/plain, Size: 1803 bytes --]

On Mon, 17 Oct 2016, Phil Blundell wrote:

> On Mon, 2016-10-17 at 07:57 -0400, Robert P. J. Day wrote:
> >
>   so is it a fair statement that, pedantically, i might as well just
> > define everything in terms of SERIAL_CONSOLES and think that way?
> >
>
> Yes.  SERIAL_CONSOLE predates SERIAL_CONSOLES and remains supported
> in the configuration for backwards compatibility.  New
> configurations and recipes should probably use SERIAL_CONSOLES and
> ignore SERIAL_CONSOLE entirely.

  i'm good with that, thanks, and one more question related to setting
baud rate for the console port, if i may. what is the precedence order
for the baud rate that is actually used, given that there are a number
of places this can be specified?

  i'm building a systemd-based system, and i'm looking at the
do_install() code in systemd-serialgetty.bb, and as i see it, if one
is using u-boot and a device tree, the baud rate can be specified in a
number of places.

1) apparently, a number of boards defined in u-boot can set the baud
rate in their ft_board_setup() routine.

2) u-boot can pass the baud rate on the kernel command line

3) the device tree blob for the target board might have the baud rate
hard-coded in the DTB

4) using SERIAL_CONSOLES

  am i missing anything? if i follow the code, i'm sure i can puzzle
it out eventually.

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================