Register Map
13-20
13.2.5.7
Transaction Stall (STALL)
Only concerns non-isochronous endpoints.
This status bit is set at the end of a transaction if a STALL handshake packet
was returned to the USB host, and if no interrupt is pending on current buffer.
The core automatically returns a STALL packet if a valid IN token is received
by a halted TX endpoint, if a valid OUT transaction is received by an halted RX
endpoint, or if there is a request error (endpoint 0). The bit is cleared when the
local host has finished handling the corresponding interrupt (at EP_Sel bit
deselection).
0: No STALL handshake was returned.
1: A STALL handshake packet was returned.
Value after local host or USB reset is low.
13.2.5.8
Transmit Non-Acknowledge (NAK)
Only concerns non-isochronous endpoints with the Nak_En bit asserted.
This status bit is set at the end of a transaction if a NAK handshake is returned
to the USB host, and if no interrupt is pending on current buffer. The USB core
automatically returns a NAK handshake to the USB host if a valid IN token is
received by a TX endpoint or if a valid OUT transaction is received by an RX
endpoint and the FIFO_En bit is not set for the endpoint. The bit is cleared
when the local host has finished handling the corresponding interrupt (at
EP_Sel bit deselection).
0: No NAK handshake was returned (the Nak_En bit is set).
1: A NAK handshake packet was returned and the Nak_En bit is set.
Value after local host or USB reset is low.
13.2.5.9
Transaction Acknowledge (ACK)
Only concerns non-isochronous endpoints.
Set at the end of a non-transparent valid IN transaction if the data packet was
sent successfully to the USB host, and the ACK handshake was received, or
at the end of a non-transparent valid OUT transaction if the data packet was
received successfully by the USB device, and the ACK handshake was
returned. The bit is cleared when the local host has finished handling the
corresponding interrupt (at EP_Sel bit deselection).
0: No ACK handshake packet was returned.
1: An ACK handshake packet was returned.
Value after local host or USB reset is low.