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The existing SPI read command is set for half-duplex 8-bit
or 16-bit writes followed by an equivalent sized read.
This patch adds a new command, VRQ_SPI_TRANSACT, which
performs a full-duplex transaction up to 4-bytes. Since the
data buffer of the USB control transfer is not available
for outbound data on IN requests, the 4 bytes of write data
are sent through the request parameters. Enables are sent
in the previsouly unused high byte of the length parameter.
The USB field mappings are shown below. Only rising edge
and MSB operation is supported.
Field (8-bit) Description
===== =====
bmRequestType 0x80 (USB Device IN request)
bRequest 0x83 (VRQ_SPI_TRANSACT)
wValueH OUT data(0)
wValueL OUT data(1)
wIndexH OUT data(2)
wIndexL OUT data(3)
wLengthH SPI enables
wLengthL Number of bytes to transfer (1-4)
EP0BUF IN data
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