Note:
Double-packet buffering is disabled if an endpoint’s corresponding EPn bit is set in the USB Transmit
Double Packet Buffer Disable (USBTXDPKTBUFDIS) register. This bit is set by default, so it must be cleared to
enable double-packet buffering.
17.2.1.1.2 Out Transactions as a Device
When in device mode, OUT transactions are handled through the USB controller receive FIFOs. The sizes of
the receive FIFOs for the configurable OUT endpoints are determined by the USB Receive FIFO Start Address
(USBRXFIFOADD) register. The maximum amount of data received by an endpoint in any packet is determined
by the value written to the USB Maximum Receive Data Endpoint n (USBRXMAXPn) register for that endpoint.
When double-packet buffering is enabled, two data packets can be buffered in the FIFO. When double-packet
buffering is disabled, only one packet can be buffered even if the packet is less than half the FIFO size.
Note:
In all cases, the maximum packet size must not exceed the FIFO size.
Single-Packet Buffering
If the size of the receive endpoint FIFO is less than twice the maximum packet size for an endpoint, only one
data packet can be buffered in the FIFO and single-packet buffering is required. When a packet is received and
placed in the receive FIFO, the RXRDY and FULL bits in the USB Receive Control and Status Endpoint n Low
(USBRXCSRL[
n
]) register are set and the appropriate receive endpoint is signaled, indicating that a packet can
now be unloaded from the FIFO. After the packet has been unloaded, the RXRDY bit must be cleared in order to
allow further packets to be received. This action also generates the acknowledge signaling to the Host controller.
If the AUTOCL bit in the USB Receive Control and Status Endpoint n High (USBRXCSRH[
n
]) register is set and
a maximum-sized packet is unloaded from the FIFO, the RXRDY and FULL bits are cleared automatically. For
packet sizes less than the maximum, RXRDY must be cleared manually.
Double-Packet Buffering
If the size of the receive endpoint FIFO is at least twice the maximum packet size for the endpoint, two data
packets can be buffered and double-packet buffering can be used. When the first packet is received and loaded
into the receive FIFO, the RXRDY bit in the USBRXCSRL[
n
] register is set and the appropriate receive endpoint
interrupt is signaled to indicate that a packet can now be unloaded from the FIFO.
Note:
The FULL bit in USBRXCSRL[
n
] is not set when the first packet is received. It is only set if a second
packet is received and loaded into the receive FIFO.
After each packet has been unloaded, the RXRDY bit must be cleared to allow further packets to be received.
If the AUTOCL bit in the USBRXCSRH[
n
] register is set and a maximum-sized packet is unloaded from the
FIFO, the RXRDY bit is cleared automatically. For packet sizes less than the maximum, RXRDY must be cleared
manually. If the FULL bit is set when RXRDY is cleared, the USB controller first clears the FULL bit, then sets
RXRDY again to indicate that there is another packet waiting in the FIFO to be unloaded.
Note:
Double-packet buffering is disabled if an endpoint’s corresponding EPn bit is set in the USB Receive
Double Packet Buffer Disable (USBRXDPKTBUFDIS) register. This bit is set by default, so it must be cleared to
enable double-packet buffering.
Universal Serial Bus (USB) Controller
1060
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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