Adafruit Ultimate GPS HAT no Serial Output

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1

Hi folks,

I have an Adafruit Ultimate GPS HAT that was working fine on an RPi4 running the latest version of Raspberry Pi OS 32-bit. I wanted to move to 64-bit so I could use some software that was for arm64 instead of armhf so I loaded that onto a new SD card after backing up the old config to carry it over.

The GPS HAT has not worked since and the only change I made was to swap the SD-cards with one running 32-bit Pi OS and the other 64-bit. The HAT still gets a fix very quickly and holds it according to the HAT LED.

Since this time, I’ve tried all kinds of isolation techniques and as it stands now, I have the HAT on a different Pi, with a fresh install of Ras Pi OS 64-bit and it’s still not seeing anything from the serial output.

This is the sum of the actions I have taken on the new device:
Logged in
Enabled serial port but disabled serial loging
Configured /boot/config.txt for dtoverlay=disable-bt
systemctl disable hciuart
systemctl disable bluetooth

This python script just hangs:

#!/usr/bin/python3
import serial
from time import sleep

ser = serial.Serial ("/dev/serial0", 9600)    #Open port with baud rate
while True:
    received_data = ser.read()              #read serial port
    sleep(0.03)
    data_left = ser.inWaiting()             #check for remaining byte
    received_data += ser.read(data_left)
    print (received_data)                   #print received data
#    ser.write(received_data)                #transmit data serially

But when the HAT is not connected the scripts give me an I/O error.
Following this doesn’t work either:Pi GPS Setup | Adafruit Ultimate GPS HAT for Raspberry Pi | Adafruit Learning System

Does anyone have any ideas please?

1 Like
2

Hi Jarrad, welcome back!

Looks like you’re not the first to have issues with serial on a 64-Bit OS:
https://forums.raspberrypi.com/viewtopic.php?t=335147

I can see you’re aware of the whole mini-uart thing, have you gone through this whole section of the Pi docs to confirm you’ve ticked all the right boxes?

1 Like
3

Hi James,

Thanks for the warm welcome.

So I have had a read of this documentation and it’s probably confused me even more.

If I am not mistaken, the UART I’m trying to enable is the PL011 UART as UART0 and my primary UART which should then in turn be on /dev/serial0 and /dev/ttyAMA0. I want to be disabling the mini-UART because this won’t function correctly.

Looking at this table: https://www.raspberrypi.com/documentation/computers/configuration.html#mini-uart-and-cpu-core-frequency has me entirely confused.

Mini UART set to core clock Result
primary UART variable mini UART disabled
primary UART fixed by setting enable_uart=1 mini UART enabled, core clock fixed to 250MHz, or if force_turbo=1 is set, the VPU turbo frequency
secondary UART variable mini UART disabled
secondary UART fixed by setting core_freq=250 mini UART enabled

This seems to suggest, to me at least, that setting enable_uart=1 will make the mini-UART the primary UART.

The default state of the enable_uart flag depends on which UART is the primary UART:

Primary UART Default state of enable_uart flag
mini UART 0
first PL011 (UART0) 1

But this second table suggests that enable_uart=0 will make the mini-UART set to the primary UART.

Should I take this to the Ras Pi forums perhaps?

I do appreciate the help!

2 Likes
4

Hi Jarrad,

I wouldn’t bother switching off the mini-UART, I didn’t when I implemented Modbus on a Pi.

Have you run a simple loopback test? screen /dev/serial0 9600 with TX shorted to RX and mashing some keys should do the trick.

Do you have access to a logic analyser or oscilloscope?

1 Like
5

Hi James,

I don’t have access to either unfortunately but I can probably create a loopback cable to test. That said, I’d rather hope I haven’t fried serial on 2 separate Pis somehow but I’ll give this a shot and report back.

Thanks

6

Hi James,

So i tried to do a loopback test. Mashing some keys didn’t yield anything but I eventually got dropped to a login screen which I thought was odd given I have disabled the console on serial.

I don’t think the cable I was using was great quality though, so I’ll go get a new one and try again, but it sounds to me like the test has failed?

I was looping pins 8 and 10.

7

Some data from dmesg.

dmesg | grep serial
[    1.603630] uart-pl011 fe201000.serial: there is not valid maps for state default
[    1.606646] uart-pl011 fe201000.serial: cts_event_workaround enabled
[    1.609463] fe201000.serial: ttyAMA0 at MMIO 0xfe201000 (irq = 19, base_baud = 0) is a PL011 rev2
[   45.632750] uart-pl011 fe201000.serial: no DMA platform data
[ 3684.249411] uart-pl011 fe201000.serial: ttyAMA0 (0): invalid RTS setting, using RTS_ON_SEND instead

I’m not sure what I am supposed to be seeing with screen /dev/serial0 9600. When I do this and mash the keyboard, it just kinda sits there and does nothing. Eventually it might clear the screen but thats it.

8

Closing this off as… turns out my poor soldering was the cause. I sorted it out and its now all working properly.

Thanks James.