NXP Semiconductors K32 L2A Series, Reference Manual, Page: 1322 / 1379

USBx_TOKEN field descriptions
Field Description
7–4
TOKENPID
Contains the token type executed by the USB module.
0001 OUT Token. USB Module performs an OUT (TX) transaction.
1001 IN Token. USB Module performs an In (RX) transaction.
1101 SETUP Token. USB Module performs a SETUP (TX) transaction
TOKENENDPT Holds the Endpoint address for the token command. The four bit value written must be a valid endpoint.
51.4.20 SOF Threshold register (USBx_SOFTHLD)
The SOF Threshold Register is used only in Host mode (CTL[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 when
SOFDYNTHLD=0, or 8 byte times when SOFDYNTHLD=1, before the SOF stops
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 peripheral device 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.
Address: 4005_5000h base + ACh offset = 4005_50ACh
Bit 7 6 5 4 3 2 1 0
Read
CNT
Write
Reset
0 0 0 0 0 0 0 0
Memory map/Register definitions
K32 L2A Reference Manual, Rev. 2, 01/2020
1322 NXP Semiconductors