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0 pointspbnjeh1y ago0 comments

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

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Dylan168071y ago

What??

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

gorkish1y ago

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

Dylan168071y ago

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.

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0 pointspbnjeh1y ago0 comments

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

0 comments

Dylan168071y ago

What??

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

gorkish1y ago

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

Dylan168071y ago

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.

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

1 more reply

j / k navigate · click thread line to collapse