USBPD EPR Request

[KamilB]

Hi! I'm working on a Power Delivery Sink using an STM32G484RETx MCU. I managed to get SPR Power Delivery working without any issues, but I'm having trouble handling the EPR handshake.

I'm using the latest USB-PD library from ST's GitHub:

https://github.com/STMicroelectronics/stm32-mw-usbpd-core

I can successfully enter EPR Mode, but the PD stack automatically calls Evaluate Capabilities and sends an SPR Request (Data Object[2] == 0). I can’t find any option to prevent the stack from running Evaluate Capabilities when Extended PDOs are received from the source.

I’ve read @FBL's post on the ST Community, which states that the latest stack should support EPR:

https://community.st.com/t5/stm32-mcus-embedded-software/update-about-usb-pd-stack-to-support-epr-mode/td-p/829168

Do you have any solutions or examples that show how to properly handle EPR using the ST USB-PD stack?

In the second screenshot, you can see that the stack incorrectly sends an EPR Request (Data Object[2] = 00000000h) because it still triggers the SPR Evaluate Capabilities callback.

Thanks.

[FBL]

Hi @KamilB 

Indeed, the stack supports it but we don't have an example to showcase the extended power range and the hardware supporting it.

[KamilB]

Hi.

I'm only interested in the communication layer. I've built my own hardware that should handle voltages up to 48V. Do you mean the STM32G4 can't handle this?

[FBL]

No @KamilB 

I mean the HW setup to manage power around the STM32 like TCPP protections provided.

[KamilB]

Hi.

Don't worry about HW. We have build our own PCB and protections on our company which are compatible with ~48V EPR voltage range. 

Can you just tell me how to send proper EPR request front STM32 to Source using ST PD Stack?

Thanks.

[FBL]

Hi @KamilB 

To create EPR request STM32 as source, here is some guidelines

1. Initialize EPR PDOs Properly : Create your EPR Source PDO PORT0_PDO_ListEPRSRC following the USB PD 3.1 AVS PDO format (voltage in 25 mV units, current in 50 mA units).

2. Assign this PORT0_PDO_ListEPRSRC and its count to the EPR PDO storage in USBPD_PWR_IF_Init.

3. Enable EPR Source support in DPM_Settings for the port to inform the PE and stack

   .Is_EPR_Supported_src=USBPD_TRUE,

4. Ensure USBPD_PWR_IF_GetPortPDOs supports USBPD_CORE_DATATYPE_SRC_PDO_EPR to handle PDO retrieval for EPR.
5. In USBPD_PWR_IF_SearchRequestedPDO, check if the requested RDO position corresponds to an EPR PDO.
6. In USBPD_PWR_IF_SetProfile,  set voltage/current to process the selected PDO type when the device receives a power contract request RDO to handle EPR voltages and currents properly (up to ~48 V).

For further details, you can refer to your ticket 00249068.

[KamilB]

Hi. I need to send a request as a sink.

Regarding point 3: If I understand correctly, you cannot notify the stack by setting something inside DPM_Settings. I can’t find any function in the examples that passes the DPM_Settings structure to the stack.