ST STM32F423 Reference Manual page 1187

RM0430
Bits 5:2 BESL[3:0]: Best effort service latency
Bit 1 LPMACK: LPM token acknowledge enable
Note: Accessible only in device mode.
Bit 0 LPMEN: LPM support enable
Host mode:
The value of BESL to be sent in an LPM transaction. This value is also used to initiate
resume for a duration T
L1HubDrvResume1
Device mode (read-only):
This field is updated with the received LPM token BESL bmAttribute when an ACK, NYET,
or STALL response is sent to an LPM transaction.
BESL[3:0]T (μs)
BESL
0000: 125
0001: 150
0010: 200
0011: 300
0100: 400
0101: 500
0110: 1000
0111: 2000
1000: 3000
1001: 4000
1010: 5000
1011: 6000
1100: 7000
1101: 8000
1110: 9000
1111: 10000
Handshake response to LPM token preprogrammed by device application software.
1: ACK
Even though ACK is preprogrammed, the core device responds with ACK only on
successful LPM transaction. The LPM transaction is successful if:
– No PID/CRC5 errors in either EXT token or LPM token (else ERROR)
– Valid bLinkState = 0001B (L1) received in LPM transaction (else STALL)
– No data pending in transmit queue (else NYET).
0: NYET
The preprogrammed software bit is over-ridden for response to LPM token when:
– The received bLinkState is not L1 (STALL response), or
– An error is detected in either of the LPM token packets because of corruption (ERROR
response).
The application uses this bit to control the OTG_FS core LPM capabilities.
If the core operates as a non-LPM-capable host, it cannot request the connected device or
hub to activate LPM mode.
If the core operates as a non-LPM-capable device, it cannot respond to any LPM
transactions.
0: LPM capability is not enabled
1: LPM capability is enabled
USB on-the-go full-speed (OTG_FS)
for host initiated resume.
RM0430 Rev 8 1187/1324
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