usrp1: Add SPI transaction command to FX2 firmware

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

1 files changed, 7 insertions, 0 deletions

diff --git a/firmware/fx2/include/usrp_commands.h b/firmware/fx2/include/usrp_commands.h
index 20c28e264..02778c7e3 100644
--- a/firmware/fx2/include/usrp_commands.h
+++ b/firmware/fx2/include/usrp_commands.h
@@ -54,6 +54,13 @@
 							// wIndexL:	format
 							// len: how much to read
 
+#define	VRQ_SPI_TRANSACT		0x83		// wValueH:  OUT byte 0
+							// wValueL:  OUT byte 1
+							// wIndexH:  OUT byte 2
+							// wIndexL:  OUT byte 3 
+							// wLengthH: enables 
+							// wLengthL: transaction length
+
 // OUT commands
 
 #define	VRQ_SET_LED			0x01		// wValueL off/on {0,1}; wIndexL: which {0,1}