[yocto] Issue with 8250/16550 UART1 access in raspberrypi (meta-raspberrypi)

[Andreas Enbacka]

Hello,

 

After a long break, I have returned to the Yocto project, and generally very
pleased. A lot of progress has been done since I last used the project (two
years ago), and now in my opinion everything works very smoothly.

 

I have used yocto to build a custom image for the RaspberryPi Compute
Module. Generally everything works ok, however I am experiencing problem
with accessing the UART1 port on the raspberryPi. I am using a library
called wiringPi to put the appropriate GPIO pins in the correct mode (alt5)
for RXD1/TXD1 (pins 32/33). Also I have used menuconfig to enable the
8250/16550 serial port support in the kernel (3.18.5+). After booting the
image I examined the dmesg output, and it shows following information
related to 8250/16550:

..

[   1.010958] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled

[   1.013920] serial8250.0: ttyS0 at MMIO 0x20215040 (irq = 29, base_baud =
7812500) is a 8250

.

 

Then I put the pins 32/33 into alternative mode alt5, and try to connect to
the port /dev/ttyS0 using minicom (baud 115200). Trying to enter something
into the Mincom terminal does not give any indications on our connected
oscilloscope (connected to the relevant pins), however change of the alt
mode earlier was observed correctly. The serial port should not be using any
flow control, but when trying to disable the flow control using Minicom (it
was on by default) freezes the complete RaspberryPi system (requiring to
disconnect and reconnect power).

 

Does anyone have any thoughts what could be the cause of these issues (e.g.,
problems with driver etc)? Any information would be greatly appreciated. In
the project we are working on we would need to use both uart ports (0/1)
provided by the compute module (the uart0 is a pl011 and by disabling
console use of /dev/ttyAMA0 we were able to successfully connect to that
port).

 

Thanks for the great work with the Yocto platform.

 

Sincerely,

Andreas Enbacka

SW designer

Gasera Ltd

 

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