RM0367 Rev 7 949/1043
RM0367 Universal serial bus full-speed device interface (USB)
955
Bits 5:4 STAT_TX [1:0]: Status bits, for transmission transfers
These bits contain the information about the endpoint status, listed in Tab le 16 9. These bits
can be toggled by the software to initialize their value. When the application software writes
‘0, the value remains unchanged, while writing ‘1 makes the bit value toggle. Hardware sets
the STAT_TX bits to NAK, when a correct transfer has occurred (CTR_TX=1) corresponding
to a IN or SETUP (control only) transaction addressed to this endpoint. It then waits for the
software to prepare the next set of data to be transmitted.
Double-buffered bulk endpoints implement a special transaction flow control, which controls
the status based on buffer availability condition (Refer to Section 32.5.3: Double-buffered
endpoints).
If the endpoint is defined as Isochronous, its status can only be “VALID” or “DISABLED”.
Therefore, the hardware cannot change the status of the endpoint after a successful
transaction. If the software sets the STAT_TX bits to ‘STALL’ or ‘NAK’ for an Isochronous
endpoint, the USB peripheral behavior is not defined. These bits are read/write but they can
be only toggled by writing ‘1.
Bits 3:0 EA[3:0]: Endpoint address
Software must write in this field the 4-bit address used to identify the transactions directed to
this endpoint. A value must be written before enabling the corresponding endpoint.
Table 166. Reception status encoding
STAT_RX[1:0] Meaning
00 DISABLED: all reception requests addressed to this endpoint are ignored.
01
STALL: the endpoint is stalled and all reception requests result in a STALL
handshake.
10 NAK: the endpoint is naked and all reception requests result in a NAK handshake.
11 VALID: this endpoint is enabled for reception.
Table 167. Endpoint type encoding
EP_TYPE[1:0] Meaning
00 BULK
01 CONTROL
10 ISO
11 INTERRUPT
Table 168. Endpoint kind meaning
EP_TYPE[1:0] EP_KIND meaning
00 BULK DBL_BUF
01 CONTROL STATUS_OUT
10 ISO Not used
11 INTERRUPT Not used
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