37.12.2 Host Start-of-Frame Control

During a very short period just before transmitting a Start-of-Frame, this register is locked. Therefore, after writing, it is recommended to check the register value, and write this register again if necessary. This register is cleared upon a USB reset.

Name:	HSOFC
Offset:	0x0A
Reset:	0x00
Property:	PAC Write-Protection


Bit	7	6	5	4	3	2	1	0
	FLENCE				FLENC[3:0]
Access	R/W				R/W	R/W	R/W	R/W
Reset	0				0	0	0	0

Bit 7 – FLENCE Frame Length Control Enable

When this bit is '1', the time between Start-of-Frames can be tuned by up to +/-0.06% using FLENC[3:0].

Note: In Low Speed mode, FLENCE must be '0'.


FLENCE	Frame Timing	Internal Frame Length Down-Counter Load Value
0	Internal Frame Length (Full Speed)	11999 (1ms frame rate at 12MHz)
0	Internal Frame Length in Low and Full speed	59999 (1ms frame rate at 60MHz)
0	Internal Frame Length in High speed	7499 (0.125ms micro-frame rate at 60MHz)
1	Beginning of Frame	FLENC[3:0]
1	Internal Frame Length with Frame correction	11999 + FLENC[3:0] at all speeds.

Value	Description
0	Start-of-Frame is generated every 1ms.
1	Start-of-Frame generation depends on the signed value of FLENC[3:0]. USB Start-of-Frame period equals 1ms + (FLENC[3:0]/12000)ms

Bits 3:0 – FLENC[3:0] Frame Length Control

These bits define the signed value of the 4-bit FLENC that is added to the Internal Frame Length when FLENCE is '1'. The internal Frame length is the top value of the frame counter when FLENCE is zero.