Virtual serial communication using esp-idf.
Long ago, most PCs had D-SUB serial ports.
When PCs had D-SUB serial ports, serial communication between two PCs was very easy.
Communication was possible with only one RS232C cross cable.
+------------+ +------------+
| PC1 | D-SUB RS232C Cross-Cable D-SUB | PC2 |
| |<-------------------------------------------->| |
| | | |
+------------+ +------------+
Before I knew it, the D-SUB serial port had disappeared from my PC, and it had changed a USB port.
Using the USB port, serial communication between two PCs looks like this.
+------------+ +------------+ +------------+ +------------+
| PC1 | USB | USB-UART | UART | USB-UART | USB | PC2 |
| | | Adapter | | Adapter | | |
| | | | | | | |
| |<--->| RX |<-------| TX |<--->| |
| | | TX |------->| RX | | |
+------------+ +------------+ +------------+ +------------+
ESP32S2/S3 has TinyUSB Serial Device function.
It can communicate with the host via USB.
By using this, serial communication can be made wireless.
+------------+ +------------+ +------------+ +------------+
| PC1 | USB | ESP32S2/S3 | WiFi | ESP32S2/S3 | USB | PC2 |
| | | | | | | |
| |<--->| |<------>| |<--->| |
| | | | | | | |
+------------+ +------------+ +------------+ +------------+
ESPNOW eliminates the need for a router.
+------------+ +------------+ +------------+ +------------+
| PC1 | USB | ESP32S2/S3 | ESPNOW | ESP32S2/S3 | USB | PC2 |
| | | | | | | |
| |<--->| |<------>| |<--->| |
| | | | | | | |
+------------+ +------------+ +------------+ +------------+
Since this application performs unicast communication, there is no limit to the order in which ESP32 is started.
The number of characters that can be read at once with tinyusb_cdcacm_read() is limited to 64 bytes.
Changing CONFIG_TINYUSB_CDC_RX_BUFSIZE does not work around this limitation.
If anyone knows a workaround, please let me know.
I (30304) tinyusb_cdc_rx_callback: CONFIG_TINYUSB_CDC_RX_BUFSIZE=256 rx_size=64
I (30304) tinyusb_cdc_rx_callback: Data from channel=0 rx_size=64
I (30304) tinyusb_cdc_rx_callback: 0x3fca6944 24 47 50 52 4d 43 2c 30 31 34 34 30 34 2c 41 2c |$GPRMC,014404,A,|
I (30314) tinyusb_cdc_rx_callback: 0x3fca6954 33 35 34 30 2e 38 38 39 35 34 36 2c 4e 2c 31 33 |3540.889546,N,13|
I (30324) tinyusb_cdc_rx_callback: 0x3fca6964 39 34 36 2e 31 38 34 35 34 30 2c 45 2c 31 36 2e |946.184540,E,16.|
I (30344) tinyusb_cdc_rx_callback: 0x3fca6974 33 2c 32 35 2e 33 2c 30 35 30 33 32 33 2c 2c 2c |3,25.3,050323,,,|
I (30354) tinyusb_cdc_rx_callback: CONFIG_TINYUSB_CDC_RX_BUFSIZE=256 rx_size=6
I (30374) tinyusb_cdc_rx_callback: 0x3fca6944 41 2a 37 42 0d 0a |A*7B..|
Data exceeding 64 bytes is divided and arrives at the other party.
Here is an example of an NMEA message over 64 bytes.
I (291393) MAIN: Wireless-->USB [$GPRMC,021613,A,3540.909988,N,13946.196413,E,16.3,25.3,050323,,,]
I (291393) MAIN: Wireless-->USB [A*7A
]
ESP-IDF V4.4/V5.0.
-
ESP32-S2/S3 Development board
Because the ESP32-S2/S3 does support USB OTG. -
USB Connector
I used this:
ESP32-S2/S3 BOARD USB CONNECTOR
+--+
| || VCC
[GPIO 19] --------> | || D-
[GPIO 20] --------> | || D+
[ GND ] --------> | || GND
+--+
git clone https://github.com/nopnop2002/esp-idf-virtual-serial-port
cd esp-idf-virtual-serial-port
idf.py set-target {esp32s2/esp32s3}
idf.py menuconfig
idf.py flash
The two ESPs must use the same port.
In order to perform UDP unicast communication, the IP address of the other party is required.
This app uses mDNS to look up peer IP addresses with the same port number.
When providing two or more sets of communication circuits, it is necessary to change the port numbers.
+------------+ +------------+ +------------+ +------------+
| PC1 | USB | ESP32S2/S3 | WiFi | ESP32S2/S3 | USB | PC2 |
| | | | PORT#1 | | | |
| |<--->| |<------>| |<--->| |
| | | | | | | |
+------------+ +------------+ +------------+ +------------+
+------------+ +------------+ +------------+ +------------+
| PC3 | USB | ESP32S2/S3 | WiFi | ESP32S2/S3 | USB | PC4 |
| | | | PORT#2 | | | |
| |<--->| |<------>| |<--->| |
| | | | | | | |
+------------+ +------------+ +------------+ +------------+
The two ESPs must use the same channel.
In order to perform ESPNOW unicast communication, the MAC address of the other party is required.
This app uses PING communication to look up peer MAC addresses with the same channel number.
When providing two or more sets of communication circuits, it is necessary to change the channel numbers.
The range of the channel of paired devices is from 1 to 14.
+------------+ +------------+ +------------+ +------------+
| PC1 | USB | ESP32S2/S3 | ESNOW | ESP32S2/S3 | USB | PC2 |
| | | | CH#1 | | | |
| |<--->| |<------>| |<--->| |
| | | | | | | |
+------------+ +------------+ +------------+ +------------+
+------------+ +------------+ +------------+ +------------+
| PC3 | USB | ESP32S2/S3 | ESPNOW | ESP32S2/S3 | USB | PC4 |
| | | | CH#3 | | | |
| |<--->| |<------>| |<--->| |
| | | | | | | |
+------------+ +------------+ +------------+ +------------+
ESPNOW's official example is here, but there are some defects.
The most egregious defect is the inability to communicate using channels other than 0 and 1.
This app solved that problem.