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RPi-Distro / pi-gen

Tool used to create the official Raspberry Pi OS images
BSD 3-Clause "New" or "Revised" License
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Unabel to see /dev/ttyAMA0 #745

Closed RosiersRobin closed 8 months ago

RosiersRobin commented 8 months ago

Hi,

I compiled the image and it worked out of the box, no biggy, however it seems I cannot see the /dev/ttyAMA0 device. It's a RPI hat plugged in (qibixx). Anyone an idea? I normally can access it via minicom and run some serial command. Now, I cannot. /dev/TTYS0 doesn't do much either.

Any ideas here?

XECDesign commented 8 months ago

I seem to have the same issue on my pi400, which only has tty[0-9]+ nodes.

What pi model are you using?

XECDesign commented 8 months ago

@pelwell

pelwell commented 8 months ago

Have you enabled the UART in the usual way (enable_uart=1 in config.txt)?

Be careful with Bookworm - config.txt has moved to /boot/firmware/config.txt; there is a symbolic link from /boot/config.txt to /boot/firmware/config.txt, but it's quite easy (with the wrong editor) to end up overwriting the symbolic link with the new, modified config.txt and leaving /boot/firmware/config.txt untouched.

pelwell commented 8 months ago

You will also not see /dev/ttyAMA0 (or whatever the Bluetooth UART is - ttyS0 if you're using the miniuart-bt overlay) because we are allowing the kernel to configure Bluetooth. The magic mechanism it is using effectively says "this is an HCI device, not a UART, so it shouldn't have a /dev/ttywhatever".

XECDesign commented 8 months ago

Using enable_uart=1 comes up with /dev/ttyS0 and then adding dtoverlay=miniuart-bt comes up with /dev/ttyAMA0 as expected.

I'll close it since it's not a pi-gen issue either way.

@RosiersRobin, if you're still having problems after setting up /boot/firmware/config.txt appropriately, let us know.

pelwell commented 8 months ago

Confirmed working as expected on a Pi 400.

To explain a bit more, the UART is not enabled by default on most (*) Bluetooth-equipped Pis. This is because UART0 (normally ttyAMA0, when not being an HCI device) is reserved for Bluetooth, leaving UART1 (ttyS0). Unfortunately the clock rate (and hence baudrate) of UART1 varies with the core clock, so to get a stable baudrate you need to stop the core clock changing, which either uses a bit more power than usual or reduces your performance, depending on whether you peg it high or low - neither of which is ideal if you don't care about the UART. That's why it's opt-in.

(*) Pi 5 is different because there are many UARTs, none of which change speed with the VPU core, so it is safe and convenient to enable the debug UART (the one on the 3-pin header) by default. To enable UART0 on the 40-pin header use dtparam=uart0=on, and to also move the boot console there use dtparam=uart0_console instead.