Table 402. Double-Buffering Buffer Flag Definition; Table 403. Bulk Double-Buffering Memory Buffers Usage - ST STM32G4 Series Reference Manual

Universal serial bus full-speed device interface (USB)
Buffer flag
The memory buffer which is currently being used by the USB peripheral is defined by DTOG
buffer flag, while the buffer currently in use by application software is identified by SW_BUF
buffer flag. The relationship between the buffer flag value and the used packet buffer is the
same in both cases, and it is listed in the following table.
Endpoint
type
IN
OUT
1. Endpoint in NAK Status.
Double-buffering feature for a bulk endpoint is activated by:
•
Writing EP_TYPE bit field at '00 in its USB_EPnR register, to define the endpoint as a
bulk, and
•
Setting EP_KIND bit at '1 (DBL_BUF), in the same register.
The application software is responsible for DTOG and SW_BUF bits initialization according
to the first buffer to be used; this has to be done considering the special toggle-only property
that these two bits have. The end of the first transaction occurring after having set
DBL_BUF, triggers the special flow control of double-buffered bulk endpoints, which is used
for all other transactions addressed to this endpoint until DBL_BUF remain set. At the end of
each transaction the CTR_RX or CTR_TX bit of the addressed endpoint USB_EPnR
register is set, depending on the enabled direction. At the same time, the affected DTOG bit
in the USB_EPnR register is hardware toggled making the USB peripheral buffer swapping
completely software independent. Unlike common transactions, and the first one after
1976/2083

Table 402. Double-buffering buffer flag definition

DTOG DTOG_TX (USB_EPnR bit 6)
SW_BUF USB_EPnR bit 14

Table 403. Bulk double-buffering memory buffers usage

DTOG SW_BUF
ADDRn_TX_0 / COUNTn_TX_0
0 1
Buffer description table locations.
ADDRn_TX_1 / COUNTn_TX_1
1 0
Buffer description table locations
0 0
1 1
ADDRn_RX_0 / COUNTn_RX_0
0 1
Buffer description table locations.
ADDRn_RX_1 / COUNTn_RX_1
1 0
Buffer description table locations.
0 0
1 1
'Transmission' endpoint
Packet buffer used by
USB peripheral
(1)
None
(1)
None
(1)
None
(1)
None
RM0440 Rev 1
'Reception' endpoint
DTOG_RX (USB_EPnR bit 14)
USB_EPnR bit 6
Packet buffer used by
Application Software
ADDRn_TX_1 / COUNTn_TX_1
Buffer description table locations.
ADDRn_TX_0 / COUNTn_TX_0
Buffer description table locations.
ADDRn_TX_0 / COUNTn_TX_0
Buffer description table locations.
ADDRn_TX_0 / COUNTn_TX_0
Buffer description table locations.
ADDRn_RX_1 / COUNTn_RX_1
Buffer description table locations.
ADDRn_RX_0 / COUNTn_RX_0
Buffer description table locations.
ADDRn_RX_0 / COUNTn_RX_0
Buffer description table locations.
ADDRn_RX_1 / COUNTn_RX_1
Buffer description table locations.
RM0440