v7 USB CDC serial data

In this document I will describe my research to make a USB serial demo.

Hardware considerations

v7 Has USB + / - exposed in the headers so you need to use an USB adapter that exposes the pins to give power to the board (VIN / GND) and connects the data to the USB+ and - data pins. OR you need to design a version which has a second USB-C port with that routed.

First example

First let's install something to send Serial data communication. In Linux I use picocom

In my branch s3_color_implementation check the example: https://github.com/vroland/epdiy/tree/s3_color_implementation/examples/tinyusb-serial

That is a very simple example that will just make v7 present itself as an "USB device" and retype characters from your keyboard in the epaper display. To do that first we need to flash the Firmware and then connecting it through this built in USB port we need to check that appears correctly using list usb:

lsusb

Bus 001 Device 00X: ID 303a:4001 Espressif Systems Espressif Device

If something like this appears, that is your S3, presenting itself as USB device. Congrats you build a USB device!

Now let's send some characters. If you check the device list:

 ls /dev/ttyA*

You should see something like /dev/ttyAC0 well that is the pipe or device file pointer to talk to this USB device. Let's open picocom and send some characters:

 picocom /dev/ttyACM0

Then just type something and it should appear in the display.

Second example (under construction)

Let's in this more advanced example receive a binary file. Since we are already decoding JPGs in another examples, let's set our mission to receive a small JPG to decode it, so we can send it "as is" to the display.

In order to do that you need to install an additional package (Only Linux example here, no idea how to do it in Windows)

  sudo apt install lrzsz

Using picocom again like in last example we can press first CRTL + A and then CTRL + S and a file prompt will appear:

Type [C-a] [C-h] to see available commands Terminal ready

*** file: martin.jpg

 $ sz -vv martin.jpg

That is supposedly opening the file with the sz program and sending it via USB serial. More to be written in this page soon!