USB on-the-go full-speed (OTG_FS) RM0008
951/1128 DocID13902 Rev 15
Figure 321. TRDT max timing case
28.17.8 OTG programming model
The OTG_FS controller is an OTG device supporting HNP and SRP. When the core is
connected to an “A” plug, it is referred to as an A-device. When the core is connected to a
“B” plug it is referred to as a B-device. In host mode, the OTG_FS controller turns off V
BUS
to conserve power. SRP is a method by which the B-device signals the A-device to turn on
V
BUS
power. A device must perform both data-line pulsing and V
BUS
pulsing, but a host can
detect either data-line pulsing or V
BUS
pulsing for SRP. HNP is a method by which the B-
device negotiates and switches to host role. In Negotiated mode after HNP, the B-device
suspends the bus and reverts to the device role.
A-device session request protocol
The application must set the SRP-capable bit in the Core USB configuration register. This
enables the OTG_FS controller to detect SRP as an A-device.
12345678
0ns 50ns 100ns 150ns 200ns
HCLK
PCLK
tkn_rcvd
dsynced_tkn_rcvd
spr_read
spr_addr
spr_rdata
srcbuf_push
srcbuf_rdata
5 Clocks
D1
A1
D1
ai15680
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