USB Controller Host and Peripheral Modes Operation | www.ti.com |
3.1.2.2.3Error Handling
If the software wants to shut down the Bulk OUT pipe, it should set the SENDSTALL bit (bit 5 of PERI_RXCSR). When the controller receives the next packet it will send a STALL to the host, set the SENTSTALL bit (bit 6 of PERI_RXCSR) and generate an interrupt.
When the software receives an interrupt with the SENTSTALL bit (bit 6 of PERI_RXCSR) set, it should clear this bit. It should however leave the SENDSTALL bit set until it is ready to
Note: If the host failed to receive the STALL packet for some reason, it will send another packet, so it is advisable to leave the SENDSTALL bit set until the software is ready to
3.1.3Interrupt Transactions
An Interrupt IN transaction uses the same protocol as a Bulk IN transaction and can be used the same way. Similarly, an Interrupt OUT transaction uses almost the same protocol as a Bulk OUT transaction and can be used the same way.
Tx endpoints in the USB controller have one feature for Interrupt IN transactions that they do not support in Bulk IN transactions. In Interrupt IN transactions, the endpoints support continuous toggle of the data toggle bit.
This feature is enabled by setting the FRCDATATOG bit in the PERI_TXCSR register (bit 11). When this bit is set, the controller will consider the packet as having been successfully sent and toggle the data bit for the endpoint, regardless of whether an ACK was received from the host.
Another difference is that interrupt endpoints do not support PING flow control. This means that the controller should never respond with a NYET handshake, only ACK/NAK/STALL. To ensure this, the DISNYET bit in the PERI_RXCSR register (bit 12) should be set to disable the transmission of NYET handshakes in
Though DMA can be used with an interrupt OUT endpoint, it generally offers little benefit as interrupt endpoints are usually expected to transfer all their data in a single packet.
40 | Universal Serial Bus (USB) Controller |
