Pedantically Pi 5 definitely uses USB-PD negotiation to negotiate with the power supply. All standards compliant USB-PD sources advertise their power modes. Some USB-C sources are PD, some (many) are not.Pi5 likely relies on USB-C Power Delivery (PD) protocol for power negotiation. Standard USB-C chargers advertise their power capabilities, allowing the Pi5 to adjust its power draw. Bypassing the adapter's internal controls might not provide a reliable 5A output. User control is limited, but some boot options might exist to override the PD negotiation.
If the Pi is powered via the GPIO pins it does not use USB-PD negotiation and will limit the max USB port current, unless this is over ridden.
The Pi 5 does not adjust its power draw per say, it does limit the maximum per USB port current it will supply if it does not successfully negotiate for a 5V/5A power mode, or if this behaviour is not overridden/disabled by the appropriate software config/switch. Limiting the max USB current will reduce the max current draw indirectly, but the Pi is not directly managing the input power.
Statistics: Posted by bjtheone — Thu Mar 14, 2024 7:29 pm