HCS08 datasheet(320/374 Pages) NXP

320 / 374 page

Universal Serial Bus Device Controller (S08USBV1)

MC9S08JM60 Series Data Sheet, Rev. 5

320

Freescale Semiconductor

2. Create BDT entries for Endpoint 0 OUT, and set the DTS and OWN bits to 1.

3. Wait for interrupt TOKDNE.

4. Read STAT register.

— The status register must show Endpoint 0, RX. If it does not, then assert the EPSTALL bit in

the endpoint control register.

5. Read Endpoint 0 OUT BD.

— Verify that the token type is a SETUP token. If it is not, then assert the EPSTALL bit in the

endpoint control register.

6. Decode and process the setup packet.

— If the direction field in the setup packet indicates an OUT transfer, then process the out data

phase to receive exactly the number of bytes specified in the wLength field of the setup packet.

— If the direction field in the setup packet indicates an IN transfer, then process the in data phase

to deliver no more than the number of bytes specified in the wLength field. Note that it is

common for the host to request more bytes than it needs, expecting the device to only send as

much as it needs to.

7. After processing the data phase (if there was one), create a zero-byte status phase transaction.

— This is accomplished for an OUT data phase (IN status phase) by setting the BC to 0 in the next

BD, while also setting OWN=1. For an IN data phase (OUT status phase), the host will send a

zero-byte packet to the device.

— Firmware can verify completion of the data phase by verifying the received token in the BD on

receipt of the TOKDNE interrupt. If the data phase was of type IN, then the status phase token

will be OUT. If the data phase was of type OUT, then the status phase token will be IN.

17.4.4.3

Endpoint 0 Exception Conditions

The USB includes a number of error checking and recovery mechanisms to ensure reliable data transfer.

One such exception occurs when the host sends a SETUP packet to a device, and the host never receives

the acknowledge handshake from the device. In this case, the host will retry the SETUP packet.

Endpoint 0 request handlers on the device must be aware of the possibility that after receiving a correct

SETUP packet, they could receive another SETUP packet before the data phase actually begins.

17.4.5

Start of Frame Processing

The USB host allocates time in 1.0 ms chunks called “Frames” for the purposes of packet scheduling. The

USB host starts each frame with a broadcast token called SOF (start of frame) that includes an 11-bit

sequence number. The TOKSOF interrupt is used to notify firmware when an SOF token was received.

Firmware can read the current frame number from the FRMNUML/FRMNUMH registers.

In general, the SOF interrupt is only monitored by devices using isochronous endpoints to help ensure that

the device and host remain synchronized.

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