38.6.2.10 STALL Request

For each endpoint, the STALL management is performed using:

• the STALL Request (USBHS_DEVEPTIMRx.STALLRQ) bit to initiate a STALL request,
• the STALLed Interrupt (USBHS_DEVEPTISRx.STALLEDI) bit, which is set when a STALL handshake has been sent.

To answer the next request with a STALL handshake, USBHS_DEVEPTIMRx.STALLRQ has to be set by writing a one to the STALL Request Set (USBHS_DEVEPTIERx.STALLRQS) bit. All following requests are discarded (USBHS_DEVEPTISRx.RXOUTI, etc. is not be set) and handshaked with a STALL until the USBHS_DEVEPTIMRx.STALLRQ bit is cleared, which is done when a new SETUP packet is received (for control endpoints) or when the STALL Request Clear (USBHS_DEVEPTIMRx.STALLRQC) bit is written to one.

Each time a STALL handshake is sent, the USBHS_DEVEPTISRx.STALLEDI bit is set by the USBHS and the PEP_x interrupt is set.

Special Considerations for Control Endpoints

If a SETUP packet is received into a control endpoint for which a STALL is requested, the Received SETUP Interrupt (USBHS_DEVEPTISRx.RXSTPI) bit is set and USBHS_DEVEPTIMRx.STALLRQ and USBHS_DEVEPTISRx.STALLEDI are cleared. The SETUP has to be ACKed.

This simplifies the enumeration process management. If a command is not supported or contains an error, the user requests a STALL and can return to the main task, waiting for the next SETUP request.

STALL Handshake and Retry Mechanism

The retry mechanism has priority over the STALL handshake. A STALL handshake is sent if the USBHS_DEVEPTIMRx.STALLRQ bit is set and if no retry is required.