Texas Instruments TMS320DM357 - Manual (Page 28)

3.1.1.3 Read Requests
USB Controller Host and Peripheral Modes Operation www.ti.com
If the length of the data associated with the request (indicated by the wLength field in the command) is
greater than the maximum packet size for endpoint 0, further data packets will be sent. In this case,
PERI_CSR0 should be written to set the SERV_RXPKTRDY bit, but the DATAEND bit should not be set.
When all the expected data packets have been received, the PERI_CSR0 register should be written to set
the SERV_RXPKTRDY bit and to set the DATAEND bit (indicating that no more data is expected).
When the host moves to the status stage of the request, another endpoint 0 interrupt will be generated to
indicate that the request has completed. No further action is required from the software, the interrupt is
just a confirmation that the request completed successfully.
If the command is an unrecognized command, or for some other reason cannot be executed, then when it
has been decoded, the PERI_CSR0 register should be written to set the SERV_RXPKTRDY bit (bit 6) and
to set the SENDSTALL bit (bit 5). When the host sends more data, the controller will send a STALL to tell
the host that the request was not executed. An endpoint 0 interrupt will be generated and the SENTSTALL
bit of PERI_CSR0 (bit 2) will be set.
If the host sends more data after the DATAEND has been set, then the controller will send a STALL. An
endpoint 0 interrupt will be generated and the SENTSTALL bit of PERI_CSR0 (bit 2) will be set.
Read requests have a packet (or packets) of data sent from the function to the host after the 8-byte
command. Examples of Read Standard Device Requests are:
•
GET_CONFIGURATION
•
GET_INTERFACE
•
GET_DESCRIPTOR
•
GET_STATUS
•
SYNCH_FRAME
The sequence of events will begin, as with all requests, when the software receives an endpoint 0
interrupt. The RXPKTRDY bit of PERI_CSR0 (bit 0) will also have been set. The 8-byte command should
then be read from the endpoint 0 FIFO and decoded. The PERI_CSR0 register should then be written to
set the SERV_RXPKTRDY bit (bit 6) (indicating that the command has read from the FIFO).
The data to be sent to the host should then be written to the endpoint 0 FIFO. If the data to be sent is
greater than the maximum packet size for endpoint 0, only the maximum packet size should be written to
the FIFO. The PERI_CSR0 register should then be written to set the TXPKTRDY bit (bit 1) (indicating that
there is a packet in the FIFO to be sent). When the packet has been sent to the host, another endpoint 0
interrupt will be generated and the next data packet can be written to the FIFO.
When the last data packet has been written to the FIFO, the PERI_CSR0 register should be written to set
the TXPKTRDY bit and to set the DATAEND bit (bit 3) (indicating that there is no more data after this
packet).
When the host moves to the status stage of the request, another endpoint 0 interrupt will be generated to
indicate that the request has completed. No further action is required from the software: the interrupt is
just a confirmation that the request completed successfully.
If the command is an unrecognized command, or for some other reason cannot be executed, then when it
has been decoded, the PERI_CSR0 register should be written to set the SERV_RXPKTRDY bit (bit 6) and
to set the SENDSTALL bit (bit 5). When the host requests data, the controller will send a STALL to tell the
host that the request was not executed. An endpoint 0 interrupt will be generated and the SENTSTALL bit
of PERI_CSR0 (bit 2) will be set.
If the host requests more data after DATAEND (bit 3) has been set, then the controller will send a STALL.
An endpoint 0 interrupt will be generated and the SENTSTALL bit of PERI_CSR0 (bit 2) will be set.
Universal Serial Bus (USB) Controller 28 SPRUGH3 – November 2008
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