_hw_usb_softhld Union Reference

HW_USB_SOFTHLD - SOF Threshold register (RW) More...

#include <MK64F12_usb.h>

Detailed Description

HW_USB_SOFTHLD - SOF Threshold register (RW)

Reset value: 0x00U

The SOF Threshold Register is used only in Host mode (HOSTMODEEN=1). When in Host mode, the 14-bit SOF counter counts the interval between SOF frames. The SOF must be transmitted every 1ms so therefore the SOF counter is loaded with a value of 12000. When the SOF counter reaches zero, a Start Of Frame (SOF) token is transmitted. The SOF threshold register is used to program the number of USB byte times before the SOF to stop initiating token packet transactions. This register must be set to a value that ensures that other packets are not actively being transmitted when the SOF time counts to zero. When the SOF counter reaches the threshold value, no more tokens are transmitted until after the SOF has been transmitted. The value programmed into the threshold register must reserve enough time to ensure the worst case transaction completes. In general the worst case transaction is an IN token followed by a data packet from the target followed by the response from the host. The actual time required is a function of the maximum packet size on the bus. Typical values for the SOF threshold are: 64-byte packets=74; 32-byte packets=42; 16-byte packets=26; 8-byte packets=18.

Definition at line 2620 of file MK64F12_usb.h.