xc6lx45 Posted November 29, 2018 Share Posted November 29, 2018 Hi, as I may not have time for FPGA work for a while - just started in a fascinating new role related to high-speed digital diaper changing - I decided to post this now. Here's the Github repo (MIT-licensed) The project provides a very fast (compared to UART) interface via the ubiquitous FTDI chip to a Xilinx FPGA via JTAG. Most importantly, it achieves 125 us response time (roundtrip latency), which is e.g. 20..1000x faster than a USB sound card. It also reaches significantly higher throughput than a UART, since it is based on the MPSSE mode of the FTDI chip. Finally, it comes with a built-in bitstream uploader, which may be useful on its own. I implemented only the JTAG state transitions that I need but in principle this can be easily copy-/pasted for custom JTAG interfacing. So what do you get: On the software side an API (C#) that bundles transactions, e.g. scattered reads and writes, executes them in bulk and returns readback data On the RTL side a very basic 32 bit bus-style interface that outputs the write data and accepts readback data, which must be provided in time. See the caveats. In general, a significant increase in complexity over a UART. The performance comes at a price. In other words, if a UART will do the job for you, DO NOT use this project. For more info, please see the repo's readme file. For CMOD A7-35, it should build right out-of-the-box. For smaller FPGAs, comment out the block ram and memory test routines, or reduce the memory size in top.v and Program.cs. I hope this is useful. When I talked to the FTDI guys at Electronica last week I did not get the impression that USB 3.0 will make FT2232H obsolete any time soon for FPGA: They have newer chips and modules but it didn't seem nearly as convenient, e.g. the modules are large and require high density connectors. In FPGA-land, I think USB 2.0 is going to stay... Cheers Markus jpeyron 1 Link to comment Share on other sites More sharing options...
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