Troubleshooting COM port issues with the CMOD A7
A few builders have reported issues when communicating with the CMOD A7, so I thought I’d collect a quick troubleshooting guide here.
FTDI drivers
Most FPGA devices do not have any native USB communication capability. In order to obtain it, the CMOD A7 includes a dedicated USB-to-RS232 chip from Future Technology Devices International (hence the FTDI acronym), the FT2232HQ.
This device requires the installation of drivers in your computer, which are used to create a “virtual COM” port. You can get those drivers from here:
https://www.ftdichip.com/FTDrivers.htm
In theory, the Adept software should install those drivers (along with the JTAG one, which it uses). But apparently this isn’t the case for some Windows versions.
I am investigating this, yet the easy solution is to install the drivers manually (it’s a fairly simple process) and reboot your computer.
More info:
https://reference.digilentinc.com/reference/programmable-logic/cmod-a7/reference-manual#usb-uart_bridge
USB port and cable
Some computers offer USB2 and USB3 ports. While installing the firmware, please make sure you use the best USB port available. Also, get a good cable. I have programmed over 50 CMODs and haven’t seen any issues, but I read in the Digilent forums that some users have had cabling issues.
https://forum.digilentinc.com/topic/4769-vivado-hardware-manager-disconnects-cmod-a7-target-in-win7/
XLoad
Once the loader firmware has been uploaded using Adept, please make sure the CMOD isn’t powered down before running XLoad (the loader stays in the FPGA, which is volatile and serves the only purpose of writing the main image into the flash).
If you see XLoad stalling at “Erasing Flash…”, that means that it could effectively open the COM port, but it’s not getting any response from the CMOD. The most common cause of this is that… it’s the wrong port (usually the JTAG port in the CMOD).
It’s totally safe to interrupt the flashing process at any point.
If you have Vivado installed
… which it’s very likely if you had the CMOD A7 around, then the firmware installation is much easer.
Unfortunately, the CMOD A7 does not provide any tool to install a bitstream image directly into the flash memory. They count on the developer having Vivado installed. It somehow makes sense: it’s a development board, and the Vivado license is free.
They also provide the free Adept software, which loads the bitstream directly into the FPGA, but inconveniently it will be gone after power down.
That’s the only purpose of the loader file: it’ll load into the FPGA a program which receives the image from your PC, and writes it into flash.
Now, if you have Vivado, writing the flash with the synth image is a breeze. Please follow this procedure:
https://reference.digilentinc.com/learn/programmable-logic/tutorials/cmod-a7-programming-guide/start#programming_the_cmod_a7_using_quad_spi
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I’ll add to this post as I collect more useful tips and field reports.