Serial Debugging

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Buy Adapter

In online shops, there are many USB to serial adapters, which are categorized by the following chips:

  1. PL2303
  2. CH340

Generally speaking, adapters using CH340 chipset, are more stable and expensive.

Hardware Connection

Use Firefly official serial port adapter,there are three wires with different colors:

  • Black: GND,Ground, connect to GND pin of the board.
  • White: TXD,Transmit,connect to TX pin of the board.
  • Green: RXD,Receive, connect to RX pin of the board.

Note: If you use other serial port adapter TX and RX can not input and output problems, you can try to TX and RX link line

Parameter Setting

Firefly-RK3288 use the following serial parameters:

  • Baud rate: 115200
  • Data bit: 8
  • Stop bit: 1
  • Parity check: none
  • Flow control: none

Serial debugging under Windows

Install Driver

Download driver and install:

If PL2303 does not works under Win8, please find drivers with version or before.

Plug in the adapter. OS will prompt that new hardware is found and being initialized. When it finish, you can find the new COM port in the Device Manager: Ch340 com xp devicemanager.png

Install Software

Under Windows, the common softwares with serial port support are putty and SecureCRT. Putty is open source software. We give a brief introduction here. The use of SecureCRT is similar.

Download putty from [3]. We recommend to download, which contains other useful utilities.

Extract and run PUTTY.exe.

  1. Select "Connection type" to "Serial".
  2. Modify "Serial line" to the COM port found in the device manager.
  3. Set "Speed" to 115200.
  4. Click "Open" button.

Putty serial startup.png

Serial debugging under Ubuntu

There are multiple choices under Ubuntu:

  • picocom
  • minicom
  • kermit

picocom is light weight, easy to use. We introduce it here, whereas others share the similar usage.


sudo apt-get install picocom

Connect the serial adapter, and check the corresponding serial device file by checking:

$ ls /dev/ttyUSB*

We use /dev/ttyUSB0 in the following examples.


$ picocom -b 115200 /dev/ttyUSB0
picocom v1.7

port is        : /dev/ttyUSB0
flowcontrol    : none
baudrate is    : 115200
parity is      : none
databits are   : 8
escape is      : C-a
local echo is  : no
noinit is      : no
noreset is     : no
nolock is      : no
send_cmd is    : sz -vv
receive_cmd is : rz -vv
imap is        : 
omap is        : 
emap is        : crcrlf,delbs,

Terminal ready

Messages above say that Ctrl-a is the escape key. Pressing Ctrl-a Ctrl-q can quit the terminal. Besides Ctrl-q, there are several control commands frequently used:

  • Ctrl-u : increase baud rate
  • Ctrl-d : decrease baud rate
  • Ctrl-f : cycle through flow controls (RTS/CTS, XON/XOFF, and none).
  • Ctrl-y : cycle through parity check (even, odd and none).
  • Ctrl-b : cycle throught data bit (5, 6, 7, 8).
  • Ctrl-c : toggle local echo.
  • Ctrl-v : show program options (like baud rate, data bits, etc).