Debug Usage

If you are doing U-Boot or kernel development, the USB serial adapter (short for USB to serial TTL adapter) is very useful for checking the system startup log, especially when there is no graphical desktop display.

Buy Adapter

There are many USB adapter to serial port on the shop, divided by chip, there are the following:

Serial port	Maximum baud rate	Is it recommended	Evaluation	Purchase link
CP2104	2 Mbps	Yes	Support high baud rate communication, good stability and durability	点击购买
CH340	2 Mbps	No	Firefly and many customers have found in actual use that the actual baud rate of many CH340s on the market cannot reach 1.5 Mbps, which causes a lot of trouble in the development process
PL2303	1.2 Mbps	No	The maximum baud rate is less than 1.5 Mbps

Note

The default baud rate of ROC-RK3568-PC is 1500000, some USB to serial chip baud rate can not reach 1500000. The same chip may have different series, so be sure to confirm whether to support before purchasing.

Hardware Connection

Serial port to USB adapter, there are four pins:

3.3V Power, no need to connect.
GND, Ground, connect to GND pin of the board.
TXD, Transmit, connect to TX pin of the board.
RXD, Receive, connect to RX pin of the board.

Note

If you encounter the problem that TX and RX cannot input and output when using other serial adapters, you can try to exchange TX and RX connections.

ROC-RK3568-PC serial port connection diagram:

Parameter Setting

ROC-RK3568-PC uses the following serial parameters:

Baud rate: 1500000
Data bit: 8
Stop bit: 1
Parity check: none
Flow control: none

Use serial on Windows

Install Driver

Download driver and install:

After the adapter is inserted, the system will prompt for the discovery of new hardware and initialization, and then the corresponding COM port can be found in the device manager:

Install Software

Putty or SecureCRT is generally used on Windows; the free version of MobaXterm is recommended. It is a powerful terminal software, and its usage is similar to the tools above.

Download MobaXterm:

Select session as Serial.
Modify Serial port to the COM port found in the device manager.
Set Speed (bsp) to 1500000.
Click OK button.

Use serial debug on Ubuntu

There are many options available on Ubuntu:

minicom
picocom
kermit

The following shows how to use minicom.

Install minicom

sudo apt-get install minicom

After connecting the serial port line, check the serial port device file. The following example is /dev/ttyUSB0:

$ ls /dev/ttyUSB*
/dev/ttyUSB0

Run:

$ sudo minicom
Welcome to minicom 2.7
OPTIONS: I18n
Compiled on Jan  1 2014, 17:13:19.
Port /dev/ttyUSB0, 15:57:00
Press CTRL-A Z for help on special keys

Based on the above tips: Press Ctrl-a and then press Z again to bring up the help menu.

+-------------------------------------------------------------------+
|                      Minicom Command Summary                      |
|                                                                   |
|              Commands can be called by CTRL-A                     |
|                                                                   |
|               Main Functions                  Other Functions     |
|                                                                   |
| Dialing directory..D  run script (Go)....G | Clear Screen.......C |
| Send files.........S  Receive files......R | cOnfigure Minicom..O |
| comm Parameters....P  Add linefeed.......A | Suspend minicom....J |
| Capture on/off.....L  Hangup.............H | eXit and reset.....X |
| send break.........F  initialize Modem...M | Quit with no reset.Q |
| Terminal settings..T  run Kermit.........K | Cursor key mode....I |
| lineWrap on/off....W  local Echo on/off..E | Help screen........Z |
| Paste file.........Y  Timestamp toggle...N | scroll Back........B |
| Add Carriage Ret...U                                              |
|                                                                   |
|             Select function or press Enter for none.              |
+-------------------------------------------------------------------+

Press O to enter the setting interface, as follows:

           +-----[configuration]------+
           | Filenames and paths      |
           | File transfer protocols  |
           | Serial port setup        |
           | Modem and dialing        |
           | Screen and keyboard      |
           | Save setup as dfl        |
           | Save setup as..          |
           | Exit                     |
           +--------------------------+

Move the cursor to Serial port setup, press enter to enter the Serial port setup interface, then enter the letter prompted earlier, select the corresponding option, and set it as follows:

  +-----------------------------------------------------------------------+
   | A -    Serial Device      : /dev/ttyUSB0                              |
   | B - Lockfile Location     : /var/lock                                 |
   | C -   Callin Program      :                                           |
   | D -  Callout Program      :                                           |
   | E -    Bps/Par/Bits       : 1500000 8N1                               |
   | F - Hardware Flow Control : No                                        |
   | G - Software Flow Control : No                                        |
   |                                                                       |
   |    Change which setting?                                              |
   +-----------------------------------------------------------------------+

Note

Hardware Flow Control and Software Flow Control should be set to No, otherwise you may not be able to input.

After finishing the setting, go back to the previous menu and select Save setup as dfl to save as the default configuration, which will be used by default later.

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