Serial Port - try to set speed to 230400, sets to 9600

[salsanci]

Programming serial port, speeds of 57600, 115200 working ok, tried to set to 230400, found the actual serial port speed was 9600.

Verified issue by using minicom, exactly same results.

[popcornmix]

I think this is just the limit of the clock frequency used and the dividers available.

You can add a config.txt pararmeter
init_uart_clock=6000000
to double the UART clock (which will have side effect of doubling baud rate)
You will need to rebuild kernel to make the baud rates have the correct values.

[florian-z]

@popcornmix Where or What in the kernel do I have to change? I can recompiile the kernel, but I do not find the right place for my new init_uart_clock value.

I suppose UART0_CLOCK in arch/arm/mach-bcm2709/include/mach/platform.h the right place?
Use bcm2709 for RPi2 & RPi3. Use bcm2708 for other.

[popcornmix]

Do you need the uart frequency to be changed during kernel boot, or after?
What baud rate do you want?

[florian-z]

I need it after kernel boot. I am currently checking if 1Mbaud is enough. Maybe 2Mbaud.
It is working now with 1Mbaud (not yet tested with 2Mbaud).

My procedure:

• set init_uart_clock to 64MHz init_uart_clock=64000000 in config.txt
• reboot and check, if the uart clock has changed to specified value. vcgencmd measure_clock uart
• if not you may need to update pi firmware. Google rpi-update
• set UART0_CLOCK in arch/arm/mach-bcm2709/include/mach/platform.h (use bcm2709 for RPi2 & RPi3. Use bcm2708 for other). Then recompile the kernel on the Pi using this howto https://www.raspberrypi.org/documentation/linux/kernel/building.md
  Takes roughly 3h on RPi2 with -j4 (use four threads)

Did I forget to mention anything?

[popcornmix]

If you want to use a standard baud rate then recompiling the kernel shouldn't be necessary.
Some info here:
http://raspberrypi.stackexchange.com/questions/1094/how-can-i-set-the-uart-speed

[florian-z]

Excuse me, but I am not understanding what the discussion (your link) is good for? The discussion contains links that support my experience, i.e. say that kernel recompile is needed for BAUD > 230400.

Different topic: I noticed that the mini-uart on RPi3 is capable of more than 230400 by default.

I still think kernel recompiling is necessary to use high bautrates with /dev/ttyAMA0 on RPi2 (I started with ... from https://www.raspberrypi.org/downloads/raspbian/. But it would be awesome if you could show I am wrong.

RASPBIAN JESSIE LITE
Minimal image based on Debian Jessie
Version:May 2016
Release date:2016-05-27
Kernel version:4.4

[popcornmix]

Can you have a read of this: https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=113753&start=125#p801441
which may be a way of doing what you want without rebuilding kernel.

[florian-z]

My problem is now fixed, without a custom kernel.
I tried it again with a fresh SD Card (fresh raspbian minimal image from May 2016). This time I only needed to set init_uart_clock in config.txt. This is confusing me, since it did not work with the default kernel before. I have to admit, that the RPi2 used, had a fresh SD card with May 2016 image, but the Pi itself was in an unopened box from 2014 (thus with firmware from 2014).

How can I check the version of the firmware & *.dtb ? Or should I just go for 'rpi-update' on every Pi, after the apt-get update & upgrade ? I am slightly confused right now.

I need to setup a couple of RPi2 in the future and it bugs me, that I cannot clearly tell, which step made it possible so that I just have to add the 'init_uart_clock' attribute. Sadly I do not have another one here for testing it right now. I am ordering another one right now, to test it.

Thank you for your GREAT support.

[JamesH65]

Note that the Pi itself does not have 'firmware', it's all on the SD card.
So getting one out of a old box is irrelevant, everything is on the SD
card.

On 4 August 2016 at 13:54, florian-z [email protected] wrote:

My problem is now fixed, without a custom kernel.
I tried it again with a fresh SD Card (fresh raspbian minimal image from
May 2016). This time I only needed to set init_uart_clock in config.txt.
This is confusing me, since it did not work with the default kernel before.
I have to admit, that the RPi2 used, had a fresh SD card with May 2016
image, but the Pi itself was in an unopened box from 2014 (thus with
firmware from 2014).

How can I check the version of the firmware & *.dtb ? Or should I just go
for 'rpi-update' on every Pi, after the apt-get update & upgrade ?
How are those *.dtb files updated, that are mentioned in your last link?

I need to setup a couple of RPi2 in the future and it bugs me, that I
cannot clearly tell, which step made it possible so that I just have to
add the 'init_uart_clock' attribute. Sadly I do not have another one here
for testing it right now. I am ordering another one right now, to test it.

—
You are receiving this because you are subscribed to this thread.
Reply to this email directly, view it on GitHub
#78 (comment),
or mute the thread
https://github.com/notifications/unsubscribe-auth/ADqrHXkeg6wTl3oZL-YiPM3ZacYOXvzbks5qceD-gaJpZM4AGiWd
.