RM0319 datasheet(131/368 Pages) STMICROELECTRONICS

131 / 368 page

RM0319

USB 2.0 Device ports (UDC)

Doc ID 022640 Rev 3

131/368

Figure 40.

Out transaction flow in slave-only mode

High-bandwidth isochronous (ISO) transfers

In outcase of out packets (that is, coming from USB Host), the data PID received for a high-

bandwidth transaction is available in the Endpoint buffer size (in) and received packet frame

number register (out), specifically in the ISO PID field (bit [17:16]).

This 2 bit field indicates the data PID for the current packet available in the receive FIFO. For

example, if the USB Host sends three packets with a PID sequence of MDATA and DATA2,

when the application receives the interrupt for the first packet, the ISO PID field of the

maximum-size packets, this register will indicate DATA2 (2‘b10).

In case of in packets (that is, transmitted to the USB Host), the transfer is described by the

following example flow:

●

At first, write the initial data PID (bit [17:16]) in the endpoint buffer size in the Endpoint

buffer size and received packet frame number register. For example, to send three

packets in a microframe, write 2’b11 to the ISO PID field (in).

●

Write the data one maximum-size packet at a time. After writing one maximum-size

packet, perform a confirm cycle.

●

Wait for the UDC-AHB subsystem to send the iso in done interrupt, setting the iso in

done (bit [23]) field in the endpoint status register after the entire high-bandwidth

transaction is completed on the USB.

●

To change the packet number to be sent in the next microframe, the application can

now modify the iso pid (in) field in the endpoint buffer size in the Endpoint buffer size

and received packet frame number register.

RxFIFO

available?

Idle

OUT

Transaction

Write the OUT

Data in the

RxFIFO

Wait for Status

Status=Success

or ISO?

Yes

Got Status

Flush data

Yes

Confirm data &

Generate INTR

Send NAK

(for non-ISO)

Excess

read?

Idle

Read data from

RxFIFO

Transfer done

Yes

Assert error

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