open-source-silicon.dev

Q01: Is /dev/ttyUSB0 accessible? If I try to connect it with minicom -D /dev/ttyUSB0 with a setting of 115200 8N1, I get nothing. I tried with lower baud rate settings.

Q02: Is there a link that shows how to get started with programming the FPGA? Is there a default image and bistream available for this board? Should I reprogram this board with a bitstream everytime?

Hi <@U07JC2KT0RX>, have you tried checking out the <https://github.com/efabless/clear|CLEAR repo> and in particular <https://github.com/efabless/clear#steps-for-using-openfpga-to-generate-bitstream-for-sofa-fpga-fabric|the steps for generating a bitstream>? There's also the <#C076M1W2M7G|> channel here, and I believe you can also <https://discord.gg/3mx4ADh|join the QWERTY Embedded Discord server> where there is <https://discord.com/channels/728101453071384647/1253788991095050240|their own >`#clear`<https://discord.com/channels/728101453071384647/1253788991095050240| channel>. The UART I believe is hard set to 9600 baud, and I seem to recall that _one_ of the Linux tty utils (minicom, picocom, or similar) might be expecting flow control and not respond by default, but besides that the UART will only respond if the CLEAR chip's "Caravel" SoC is running firmware that actually configures and uses the UART -- and by default I don't think that would be the case. It's there if you WANT to use it for something but I don't think (or don't know) it has a specific required function for CLEAR as-is.

The Linux device driver sees an FTDI chip and automatically generates `/dev/ttyUSB0`, but that assumes that the FTDI is talking to something on the other end that is a UART.  The default configuration on the board has the FTDI talking to the housekeeping SPI, which can't be done with a UART-based serial communcation program like `minicom`, but as far as I know, can only be accessed through `pyftdi`  (which is what our scripts like `caravel_hkdebug.py` and `caravel_hkflash.py` are doing).  There are some electronic switches up in the top right-hand corner of the board (U2 and U3 on my board rev.) that can be driven by the FTDI's bit-bang bus and can be used to switch the FTDI chip output from the housekeeping SPI to the UART.  Since `minicom` is unlikely to drive the FTDI bit-bang bus, I expect it's still only accessible through `pyftdi`.  Somebody wrote a script for accessing the UART from a terminal (Jeff likely knows about it?). (The pyftdi site has a script `pyterm.py` that might be useful for that.)