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3.7.1
Autodecoded Control Write Transfers
Autodecoded Control Write Transfer Handshaking
SPRU761A
When a setup token is identified, the USB decode module must monitor the
setup stage data packet, decode it, and determine whether it is an
autodecoded or a non-autodecoded transfer and a control read or a control
write. If it is a valid non-autodecoded request, the setup FIFO is immediately
cleared and control of the FIFO is immediately taken away from the MPU (if
the MPU had control of the FIFO). New setup data are placed into the setup
FIFO, and the setup interrupt flag is set (IRQ_SRC.setup).
In response to the setup interrupt, the MPU must select the setup FIFO by
setting the EP_NUM.SETUP_SEL bit. This clears the IRQ_SRC.SETUP flag.
The MPU must then read 8 bytes from the setup FIFO, clear the
EP_NUM.SETUP_SEL bit, and confirm that IRQ_SRC.SETUP bit has not
been reset by a new setup transaction. If the IRQ_SRC.SETUP flag is
asserted, the MPU must discard the previously read data and handle the new
setup packet as explained above. Thus the MPU never misses a new
occurring setup transaction (per USB 1.1 specification).
For set address control write transfers, the USB address provided in the setup
token is captured to the USB module device address register. If new address
is different from 0, the device moves into addressed state (DEVSTAT.ADD set)
if it was not already addressed.
For set and clear feature control writes, the appropriate feature information bit
is set or cleared. When a set or clear feature transfer occurs to set or clear the
device remote wake-up feature, the DEVSTAT.R_WK_OK bit is set or cleared,
as appropriate. If a set or clear interface feature occurs, the request is
automatically stalled by the core because no feature is defined for interface
(see the USB 1.1 specification).
Per the USB 1.1 specifications, a SET_ADDRESS request is effective after the
status stage of the request, even if the status stage does not end with an ACK
handshake. SET/CLEAR_FEATURE requests are effective after setup stage,
even if no status stage occurs.
The USB device controller module automatically provides ACK handshaking
for all transactions of all stages of autodecoded control write transfers, except
if a corrupted packet is received, which the USB module ignores. The
CTRL.SET_FIFO_EN and SYSCON2.STALL_CMD bits have no effect on
handshaking.
USB Device Controller
Universal Serial Bus (USB)
127
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