GD32VF103 USB to UART bridge

This project shows how to use GD32VF103 board as USBtoUART bridge.

The project is intended to be run on Longan Nano board.
If testing on another board (without a display), edit lib/usbcdc/include/cdc_acm_core.h to remove display and/or LED support.

Features:

• The project implements USB CDC/ACM device with some additional features.
• Bridging USB to two UARTS is supported.
• Display support, displays status and statistics.
• Baudrates from 2400 ~ 4000000 Bd are supported
• Python CDC driver with examples included

Pins used for UARTs:

UART0:

• PA9 Tx
• PA10 Rx
• PA13 RTS
• PA14 DTR

UART1:

• PB10 Tx
• PB11 Rx
• PB13 RTS
• PB14 DTR

Details

After the board is connected to PC it will be enumerated as USB device 28e9:018a.

Bus 003 Device 028: ID 28e9:018a  
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            2 Communications
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  idVendor           0x28e9 
  idProduct          0x018a 
  bcdDevice            1.00
  iManufacturer           1 GigaDevice
  iProduct                2 GD32VF USB CDC ACM in FS Mode
  iSerial                 3 GD32VF-3.0.0-012020
  bNumConfigurations      1
...

The device can be accessed for serial communication as /dev/ttyACMn, for example via Minicom, Putty etc.

[24377.013615] usb 3-9: new full-speed USB device number 28 using xhci_hcd
[24377.167007] usb 3-9: New USB device found, idVendor=28e9, idProduct=018a, bcdDevice= 1.00
[24377.167011] usb 3-9: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[24377.167013] usb 3-9: Product: GD32VF USB CDC ACM in FS Mode
[24377.167015] usb 3-9: Manufacturer: GigaDevice
[24377.167017] usb 3-9: SerialNumber: GD32VF-3.0.0-012020
[24377.168506] cdc_acm 3-9:1.0: ttyACM0: USB ACM device

As the device has some non-standard CDC features, it is recommended to use it via the provided Python driver cdc_driver.py.

Switching UARTS

GD32VF103 does not have enough USB endpoints to implement a composite CDC device.
The UART ports can be changed using one of two methods:

• sending a break condition, this is usually used from standard communication program
• sending a special CDC command, this is fully supported and described in cdc_driver.py

Notes

If Longan Nano is used and USE_LEDS is enabled in configuration, green LED will be active when UART1 is selected.

If Longan Nano is used and USE_DISPLAY is enabled in configuration, UART format and DTR/RTS status will be shown on display.
Special CDC command can be used to display the communication statistics (USB number of sent/received bytes, UART number of sent/received byted, number of UART receive errors,...).

DTR and RTS outputs can be configured as push-pull or open colector (UARTn_RTS_DTR_MODE define in lib/usbcdc/include/cdc_acm_core.h).

Using break for UART change can be disabled/enabled using UART_USE_BREAK_TO_CHANGE define in lib/usbcdc/include/cdc_acm_core.h.

Functions supported in cdc_driver.py:

# -------------------------------------------------------
# Show the current status on the device display (if used)
# If the 'reset' argument is 1, reset the counters
# -------------------------------------------------------
showStatus(reset = 0)

# -----------------------------------
# Set DTR and RTS line state
# -----------------------------------
setLineState(dtr=1, rts=1)

# ------------------------------------------------------
# Set active device UART, 0 or 1 can be used as argument
# ------------------------------------------------------
setUART(uartno=0)

# -----------------------------------------------------------
# Set the UART communication format
#    bdr: baudrate, 2400 - 4000000
#   bits: 8 or 7
# parity: 0 - None; 2 - Even, 3 - Odd
#   stop: number of stop bits; 0 = 1, 1 = 0.5, 2 = 2, 3 = 1.5
# -----------------------------------------------------------
setFormat(bdr=115200, bits=8, parity=0, stop=0)

# ----------------------------------------------------------
# Get the current UART communication format from the device
# If 'prn' argument is True, prints the format
# Returns tuple: (bdr, stop, parity, bits)
# ----------------------------------------------------------
getFormat(prn=False)

# --------------------------------------------
# Get the current transmition status
# If 'prn' argument is True, prints the status
# Returns tuple:
#   (
#    active_uart,
#    dtr_state,
#    rts_state,
#    usb_sent,
#    usb_received,
#    uart_sent,
#    uart_received,
#    uart_receive_errors
#   )
# --------------------------------------------
getStatus(prn=False)

# -------------------------------------------------
# Return number of received bytes in receive buffer
# -------------------------------------------------
received()

# ----------------------------------
# Read data from receive buffer
# count: max number of bytes to read
# Returns array of bytes
# ----------------------------------
read(count=1)

# -------------------------------------------------
# Read data from receive buffer converted to string
# count: max number of bytes to read
# -------------------------------------------------
readString(count=1)

# --------------------
# Write data
# --------------------
write(data)