I'm working with the FX3 DVK, following the application notes AN65974 to perform stream_in, stream_out and loopback transfer with my Xilinx FPGA. When performing stream_in and stream_out transfer, it seems quite ok.
However, during loopback transfer, after transfer data out, when I was trying to read data back from bulk in endpoint, it shows that zero length data transfered. I think the communication betwwen FX3 and FPGA failed. So I tried to capture how each control signal data react from FPGA side during transfer. I found that my flagd is always 1 and never changed to 0 and my flagc once changed from 0 to 1, never changed back to 0. As a result, SLRD# keeps asserted during the whole process. Btw, I used the firmware code provided by Cypress and the flag configuration is just same.