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12-24 Intel® PXA255 Processor Developer’s Manual
USB Device Controller
12.6.2 UDC Control Function Register (UDCCFR)
The UDC Control Function register (UDCCFR) contains 1 mode bit and 1 enable bit that lets
software delay sending back an ACK response to SET_CONFIG or SET_INTERFACE commands
from the host. The remaining bits are reserved and should not be written.
12.6.2.1 ACK Control Mode
The ACK control mode (ACM) bit enables user control of the ACK response to the status IN
requests of SET_CONFIGURATION and SET_INTERFACE commands. When ACM is set to 0,
the UDC automatically responds to the STATUS IN request following a SET_CONFIGURATION
and SET_INTERFACE with an ACK. When ACM is set to 1, the UDC responds to the STATUS
IN request following a SET_CONFIGURATION and SET_INTERFACE command with a NAK
until AREN is set to 1. When the user sets AREN to 1, the UDC responds with an ACK to the next
STATUS IN request.
12.6.2.2 ACK Response Enable
When ACM = 1, the ACK response enable (AREN) bit enables user control of the ACK response
to the status IN requests of SET_CONFIGURATION and SET_INTERFACE commands. When
ACM is set to 1, the UDC responds to the STATUS IN request following a
SET_CONFIGURAION and SET_INTERFACE command with a NAK until AREN is set to 1.
When the user sets AREN to 1, the UDC responds with an ACK to the next STATUS IN request.
AREN is cleared by the UDC when another SETUP command is received.
Table 12-13. UDC Control Function Register
0h 4060 0008 UDCCFR Read/Write and Read-Only
Bit
31:8 7 6 5 4 3 2 1 0
Reserved AREN Reserved Reserved Reserved Reserved ACM UDA UDE
Reset
X 1 1 0 1 1 1 1 0
Bits Name Description
31:8 — Reserved – Read as unknown and must be written as zero.
7AREN
ACK RESPONSE ENABLE (read/write 1 to set)
0 – Send NAK response to SET_CONFIGURATION and
SET_INTERFACE commands
1 – Send ACK response to SET_CONFIGURATION and
SET_INTERFACE commands
6 — Reserved – Read as unknown and must be written as zero.
5 — Reserved – Read as unknown and must be written as zero.
4 — Reserved – Read as unknown and must be written as zero.
3 — Reserved – Read as unknown and must be written as zero.
2ACM
ACK CONTROL MODE (read/write 1 to set)
0 – Send ACK response to SET_CONFIGURATION and
SET_INTERFACE commands with no user intervention
1 – Send NAK response to SET_CONFIGURATION and
SET_INTERFACE commands until UDCCFR[AREN] = 1
1 — 1 – Reserved – Read as unknown and must be written as zero.
0 — 1 – Reserved – Read as unknown and must be written as zero.