Hi JL46,
1. What I have understood from your question is the 4 unused data bits of GPIF has to be initialized as HIGH and kept HIGH throughout the transfer. If its correct, GPIO4-7 can be pulled up using a resistor externally.
Also other GPIOs apart from DQ0-DQ7 can be used and initialized in the firmware.
2. There are two methods for reading the sampled data through control center,
a. You could declare a global flag, and change its value only when a particular vendor command is received by the firmware. Then you can check for this flag in the GpifToUsbDmaCallback and depending on the value of the flag, you could either discard or commit the buffer accordingly.
b. In the GPIF state machines, in the transition equations, there is FW_TRG. You could use (!DRDY&FW_TRG) in the GPIF transition equation (STATE0 -> STATE1) and in the firmware, call the CyU3PGpifControlSWInput() API when a particular vendor command is received. For more information on this API, refer to Pg No. 263 of the FX3APIGuide.
3. When you double-click on a state, you can set how many times the state has to be repeated. So for the GpifToUsb project which I have shared with you, I have specified this value to be 32 for STATE1. I have attached a snapshot for your reference. So yes, 32 bits will be read from a GPIO synchronously with clk and drdy.
Best Regards,
AliAsgar
