<![CDATA[ESP-NOW uiflow callback function not triggering]]>Hello All,
I cannot get the uiflow espnow callback (espnow.recv_cb(recv_cb)) to trigger from espnow messages sent from an Arduino IDE based or none-M5Stack micropython based ESP32. I can send and receive espnow data between 2 Arduino IDE based ESP32s. I can also send and receive espnow data between 2 uiflow M5Stack ESP32s. And I can also send and receive espnow data between an Arduino IDE and none-M5Stack micopython based ESP32.

I using a Core2 and M5StickC Plus for testing.

The message is sent successfully based on esp_now_register_send_cb(OnDataSent); callback function in Arduino IDE. And if I power down the uiFlow ESP32 device the message fails to send, expected behavior. So I believe everything it set up correctly.

I can send data from a uiFlow ESP32 to a Arduino IDE based ESP32. Although there seems to be a data alignment issue.

Has anyone been able to send espnow messages from a non-uiflow ESP32 to a uiflow ESP32?

How this make sense!

Thank you
Austin

]]>https://community.m5stack.com/topic/4165/esp-now-uiflow-callback-function-not-triggeringRSS for NodeWed, 29 Apr 2026 16:18:22 GMTTue, 29 Mar 2022 23:16:29 GMT60<![CDATA[Reply to ESP-NOW uiflow callback function not triggering on Mon, 04 Apr 2022 18:39:18 GMT]]>Hello M5Stack,
Can you please post the function used to create the 10 bytes of preData when sending an espnow message from a device coded with uiFlow?

This will allow us to send espnow messages from devices not coded with uiFlow to devices coded in uiFlow.

Thanks you
Austin

]]>https://community.m5stack.com/post/17091https://community.m5stack.com/post/17091Mon, 04 Apr 2022 18:39:18 GMT<![CDATA[Reply to ESP-NOW uiflow callback function not triggering on Thu, 31 Mar 2022 13:20:37 GMT]]>Hello All,
Me again. After doing some testing I determined that the uiFlow code is adding 10 bytes of information (preData) to the beginning of the text being sent. Maybe some type of checksum. This can be seem here.

Most the preData bytes are constant, either 1 or 0. Below is preData I created in the Arduino IDE and sent to a M5StickC Plus to get the receive callback to be triggered.

// Sent from Arduino IDE, ESP32, #include <esp_now.h>
// The 3 combinations for header3, header5, header6 and cmd after the comment (//) trigger the uiFlow receive callback.
// Changing any of the values causes the uiFlow receive callback not be to triggered
// There must be a some type of checksum calculation within the M5Stack uiFlow code.
data.header1 = 1;
data.header2 = 1;
data.header3 = 0;   // 0, 1, 2  Seems to be a counter, rolling over a 255
data.header4 = 0;
data.header5 = 222; // 222, 249, 144 Seems to be a checksum of some kind
data.header6 = 67;  // 67, 111, 27 Seems to be a checksum of some kind
data.header7 = 0;
data.header8 = 0;
data.header9 = 0;
data.header10 = 0;
strcpy(data.cmd, "on");// on, on, on
esp_now_send(broadcastAddress, (uint8_t *)&data, sizeof(data));

Can someone point me to the code which creates the 10 bytes of information?

Thanks You
Austin

]]>https://community.m5stack.com/post/17063https://community.m5stack.com/post/17063Thu, 31 Mar 2022 13:20:37 GMT