NXP Semiconductors K32 L2A Series, Reference Manual, Page: 1336 / 1379

1. Complete all steps to discover a connected device and to configure a connected
device. Write the ADDR register with the address of the peripheral device. Typically,
there is only one other device on the USB bus in host mode so it is expected that the
address is 0x01 and should remain constant.
2. Write 0x1D to ENDPT0 register to enable transmit and receive transfers with
handshaking enabled.
3. Setup the even TX EP0 BDT to transfer up to 64 bytes.
4. Set the USB device address of the peripheral device in the address register
(ADDR[6:0]).
5. Write the TOKEN register with an OUT token to the desired endpoint. The write to
this register triggers the USB-FS transmit state machines to begin transmitting the
token and the data.
6. Setup the odd TX EP0 BDT to transfer up to 64 bytes.
7. Write the TOKEN register with an OUT token as in step 4. Two tokens can be
queued at a time to allow the packets to be double buffered to achieve maximum
throughput.
8. Wait for the TOKDNE interrupt. This indicates that one of the BDTs has been
released back to the processor and the transfer has completed. If the peripheral device
asserts NAKs, the USB-FS continues to retry the transfer indefinitely without
processor intervention unless the ENDPT0[RETRYDIS] is 1. If the retry disable field
is set, the handshake (ACK, NAK, STALL, or ERROR (0xf)) is returned in the BDT
PID field. If a stall interrupt occurs, the pending packet must be dequeued and the
error condition in the peripheral device cleared. If a Reset interrupt occurs (SE0 for
more than 2.5 μs), the peripheral device has detached.
9. After the TOK_DNE interrupt occurs, the BDTs can be examined and the next data
packet queued by returning to step 2.
51.7 On-The-Go operation
The USB-OTG core provides sensors and controls to enable On-The-Go (OTG)
operation. These sensors are used by the OTG driver software to implement the Host
Negotiation Protocol (HNP) and Session Request Protocol (SRP) and give access to the
OTG protocol control signals. The following state machines show the OTG operations
involved with HNP and SRP protocols from either end of the USB cable.
On-The-Go operation
K32 L2A Reference Manual, Rev. 2, 01/2020
1336 NXP Semiconductors