Texas Instruments OMAP5912 Reference Manual page 1418

USB Device Controller
126 Universal Serial Bus (USB)
Non-autodecoded control read and control write transfers are sets of
transactions that occur on endpoint 0 and have specific USB protocol meaning
but are not handled automatically by the core. The USB device controller block
automatically provides an ACK handshake for the setup stage transaction, but
the data and status stage transaction handshaking is accomplished using the
usual RX and TX control bits that affect transaction handshaking. A general
USB interrupt to the MPU occurs at the end of each transaction of each stage
of a control transfer. The MPU must perform the following actions to act on
non-autodecoded control transfers:
-
Process the setup phase setup USB interrupt. The MPU reads the control
transfer command from the setup FIFO and decodes the command. For
control reads, the MPU fetches the requested read data and places it (or
as much of the read data as fits) into the endpoint 0 FIFO, and then
enables the endpoint 0 FIFO. For control writes, the MPU code only
enables the endpoint 0 FIFO. MPU code also sets any flags needed for
processing endpoint 0 USB interrupts during the control transfer.
-
Process the data phase endpoint 0 general USB interrupt(s). For control
reads, the data phase general USB endpoint 0 TX interrupt indicates that
the previously provided transmit data has been sent. Any additional data
must be written to the endpoint 0 FIFO. For control writes, the write data
must be pulled from the endpoint 0 FIFO, and when all control write data
is available, interpret the write data and act on the write request. After
handling the last data phase interrupt, the MPU must set the endpoint 0
control bits to signal the desired status to the host.
-
Process the status stage endpoint 0 general USB interrupt. The MPU
provides its completion status back to the USB host during this stage,
either via status in the data phase of the transaction (for control write
transfers) or via the handshake phase of the transaction (for control read
transfers).
Autodecoded control read and control write transfers are sets of transactions
that occur on endpoint 0 that have specific USB protocol meaning and are
handled automatically by the USB device controller block without any
intervention by the MPU. The USB device controller block handles all
handshaking automatically and without regard to the endpoint 0 control bits
that affect normal (non-control transfer) transaction handshaking. No interrupt
is asserted to the MPU during autodecoded control transfers.
If no USB1.1 specification defined request is associated with the data of the
setup phase, request is stalled by the core and the MPU is not informed of its
occurrence (autodecoded).
SPRU761A