[pbnjeh]

I don't have Pi 5 to check this, but from what I've read, it does not support PPS. And such support is required; otherwise, even with a source that supports PPS, the connection will behave in a non-PPS fashion.

Apparently, cable quality is also demonstrating itself to be a significant factor in the Pi 5 power supply environment.

Regarding both these points:

https://github.com/raspberrypi/rpi-eeprom/issues/497

[Dylan16807]

What??

Then how the hell does it negotiate the power and know if it's attached to 3A or 5A?

[gorkish]

Well, as it turns out, although a lot of stuff out there implies that the Pi uses USB-PD, it actually doesn't negotiate anything; it's just a dumb 5V peripheral. It can measure its own power (current/voltage) and has a current limit setting that the PMC will use to adjust clocks, etc. and alert on overcurrent conditions. If you hook up a higher amperage supply you have to change your boot config to the higher current limit. Everything is on you to make it work its weird not-quite-standards-compliant way.

The "Official Pi 5 USB-C Power Supply" is USB-PD compliant and as it is advertised as such in conjunction with the Pi5, I think that is where the confusion originates

[Dylan16807]

I thought the boot config was just an override.

The things I've been searching in the last few minutes suggest that the Pi can negotiate 5A but only if the power supply explicitly offers it as a PDO, which almost nothing does.

But even if that's right, it's almost as bad as not doing PD at all.

Edit: The documentation states "If the Raspberry Pi 5 firmware detects a supported 5A-capable supply, it increases the USB current limit for peripherals to 1.6A, providing 5W of extra power for downstream USB devices, and 5W of extra onboard power budget."

It also confirms no PPS, but it's not entirely dumb.

[gorkish]

That may indeed be correct at least in some circumstances; maybe it at least works with some capability of the offical supply. In my experience I have had to use usb_max_current_enable=1 and PSU_MAX_CURRENT=5000 to get it to shut up and work.

Here's the thing though; the simple fact that we have to even have this discussion because the Rpi5 continues to be super damn weird is enough evidence for me that the platform has jumped the shark. I don't know whether to blame Broadcom or the Pi Foundation, but the Pi 5 suuuuuucks. Man, I wanted to love it though; it's the only board I have even been been able to buy from them in the last FOUR YEARS

[Dylan16807]

Agreed, I'm very annoyed it doesn't support PPS. A whole host of issues made me buy a small pc instead recently and the price difference was negligible.