I've followed the instructions found in cyusb_mac_user_guide.pdf to build/install CyUSB Suite for Mac OS. I've gotten to the point where I can read/write data to the FX3:
$ ./cybulk_writer 512
The Endpoint address is 0x1
Successfully transferred 512 bytes
However, when trying to program the FX3, I am getting a "Vendor write to FX3 RAM failed":
$ ./download_fx3 -i /Workspace/GpifToUsb/Debug/GpifToUsb.img -t RAM
Error: Vendor write to FX3 RAM failed
Error: Failed to download data to FX3 RAM
Error: FX3 firmware programming failed
I built the GpifToUsb example found in /cyfx3sdk/firmware/basic_examples/cyfxgpiftousb. Plugged the FX3 SuperSpped Explorer Kit via USB and the blue LED is continuously blinking. At that point, I try to flash the GpifToUsb.img file and get that error.
It looks you are operating the FX3 in I2C fallback to Usb Boot Mode. Hence, the bootloader loads the preloaded firmware from EEPROM and LED starts blinking.
If you want to program the FX3 with GpifToUsb example firmware, you need to set the PMODE lines of FX3 to USB Bootloader Mode (PMODE[2:0] = Z11).