UART not transmitting data (solved)

[pete-theobald]

Hi Everyone,

I'm completely stumped by a problem with my raspberrypi board and hoping someone can help. I have a board connected to the gpio header, the board has a pic which sends a message which the pi receives. I've checked this with a screen session connected to ttyAMA0. I've tried to transmit characters back to the pic but they aren't received. I investigated a bit further and it looks like the pi isn't sending the characters in the first place. I connected a scope to the TXD pin on the GPIO and then use a python script to send messages as follows

Code: Select all

import serial
serialPort = serial.Serial("/dev/ttyAMA0", 9600, timeout=0.5, rtscts=False, dsrdtr=False, xonxoff=False,bytesize=serial.EIGHTBITS,parity=serial.PARITY_NONE)
while True:
    serialPort.write("Hello world!")
    serialPort.flush()

Theres no signal coming from the tXD pin at all. When I send data to the pi frmo the pic, it receives it fine so I don't think I have the pins the wrong way round. That also shows that I have the right pin as I have gnd, TXD and RXD in a row (Also no signal on any pin).

Is there any chance i've blown up the uart? I have the data passing through an isolator with the pi side run off the 3.3v pin of the GIPO so very unlikely.

Regards
Pete

[PeterO]

Have you disabled the kernel log output on /dev/ttyAMA0 ?
Remove "console=ttyAMA0,115200 kgdboc=ttyAMA0,115200" from /boot/cmdline.txt

Also you need to comment out the second line below at the bottom of /etc/inittab
#Spawn a getty on Raspberry Pi serial line
#T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

Also, have you tried looping the pi back to itself by connecting the TxD and RxD together ? Then you can run a terminal program like minicom (you may need to install this first) and see if the typed characters are received and displayed.


HTH
PeterO

[pete-theobald]

Thanks for the reminder!
I had already commented out the line in inittab and removed it from cmdline.txt but thats exactly what I was trying to check.
Its started working now which is strange. I was checking the wrong pins with the scope but that doesnt explain why it didnt show up when I tested every pin in turn (probably a gnd error as I had the pins on the wrong row).
Now I need to work out why my pic won't receive any characters...
Pete

[DexOS]

What Baud are you using ? and does the pic code use ints ?

[pete-theobald]

What Baud are you using ? and does the pic code use ints ?

I managed to receive characters earlier but not reliably. 115200 baud. The pic is running freertos so I have a wrapper around the uart to stop any clashes between threads. I can handle single chars but it drops lines if I try and put chars back into lines. That's tomorrow's job to fix though! Receive code is using an interrupt but it pushes chars into a freertos queue which is read from a thread.
Pete

[DexOS]

From my experience, it sounds like a baud rate problem.
Have you tried a lower rate ?.

[pete-theobald]

It was much simpler than that, I had a small solder bridge between the TX and another pin so a soldering iron and some copper braid sorted it out. The pics a QFN package and they're a real pain to solder!!! Its working at 115200 again now.
Pete