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Registers
1698
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Universal Serial Bus 2.0 (USB) Controller
34.4.6 Auto Request Register (AUTOREQ)
The auto request register (AUTOREQ) allows the CPU to enable an automatic IN token request
generation for host mode RX operation per each RX endpoint. This feature has the DMA set the REQPKT
bit in the control status register for host receive endpoint (HOST_RXCSR) when it clears the RXPKTRDY
bit after reading out a packet. The REQPKT bit is used by the core to generate an IN token to receive
data. By using this feature, the host can automatically generate an IN token after the DMA finishes
receiving data and empties an endpoint buffer, thus receiving the next data packet as soon as possible
from the connected device. Without this feature, the CPU will have to manually set the REQPKT bit for
every USB packet.
There are two modes that auto request can function in: always or all except an EOP. The always mode
sets the REQPKT bit after every USB packet the DMA receives thus generating a new IN token after each
USB packet. The EOP mode sets the REQPKT bit after every USB packet that is not an EOP (end of
packet) in the CPPI descriptor. For RNDIS, CDC, and Generic RNDIS modes, the auto request stops
when the EOP is received (either via a short packet for RNDIS, CDC, and Generic RNDIS or the count is
reached for Generic RNDIS), making it useful for starting a large RNDIS packet and having it auto
generate IN tokens until the end of the RNDIS packet. For transparent mode, every USB packet is an
EOP CPPI packet so the auto request never functions and acts like auto request is disabled.
The AUTOREQ is shown in
and described in
Figure 34-32. Auto Request Register (AUTOREQ)
31
16
Reserved
R-0
15
8
7
6
5
4
3
2
1
0
Reserved
RX4_AUTREQ
RX3_AUTREQ
RX2_AUTREQ
RX1_AUTREQ
R-0
R/W-0
R/W-0
R/W-0
R/W-0
LEGEND: R/W = Read/Write; R = Read only; -
n
= value after reset
Table 34-36. Auto Request Register (AUTOREQ) Field Descriptions
Bit
Field
Value
Description
31-8
Reserved
0
Reserved
7-6
RX4_AUTREQ
0-3h
Receive endpoint 4 auto request enable
0
No auto request
1h
Auto request on all but EOP
2h
Reserved
3h
Auto request always
5-4
RX3_AUTREQ
0-3h
Receive endpoint 3 auto request enable
0
No auto request
1h
Auto request on all but EOP
2h
Reserved
3h
Auto request always
3-2
RX2_AUTREQ
0-3h
Receive endpoint 2 auto request enable
0
No auto request
1h
Auto request on all but EOP
2h
Reserved
3h
Auto request always
1-0
RX1_AUTREQ
0-3h
Receive endpoint 1 auto request enable
0
No auto request
1h
Auto request on all but EOP
2h
Reserved
3h
Auto request always