Classical Bluetooth SPP send throughput is very slow to Android (IDFGH-466)

[copercini]

When sending data using esp_spp_write() at more than ~ 5KB/s to an Android phone, it triggers a lot of ESP_SPP_CONG_EVT events and the communication slow down, this problem doesn't occur in other systems, like a Windows PC with the same ESP code

Commenting out this line as proposed by Markus Becker, this issue seems less frequent and no more ESP_SPP_CONG_EVT events with a high throughput

More discussion about this problem, and workaround: https://www.esp32.com/viewtopic.php?t=5613

[blueMoodBHD]

Hi @copercini , There is one thing that needs attention here. We can't call esp_spp_write() multiple times in succession. We should wait for ESP_SPP_WRITE_EVT, then call esp_spp_write() again.
So, when do you call esp_spp_write()？If you call it multiple times in succession, please change it and test again.
Thanks.

[copercini]

@blueMoodBHD it's already implemented here and here, the packets are queued and only written after get the previous packet ESP_SPP_WRITE_EVT and check if ESP_SPP_CONG_EVT is free to send

If you use arduino core for ESP32, you can test it using this simple code:

#include "BluetoothSerial.h"

BluetoothSerial SerialBT;

void setup() {
  Serial.begin(115200);
  SerialBT.begin("ESP32test"); //Bluetooth device name
  Serial.println("The device started, now you can pair it with bluetooth!");
}

void loop() {
  SerialBT.printf("abcdefghjklmnopqrstuvxwyz");
  delay(10); //If this delay is lower, the data rate if faster, causing a lot of transmission issues to Android, but not to others systems like Windows
}

Hi @copercini

Please pull the latest IDF and have a try. We have merged two MR related to SPP flow control. It will take several days to sync on Github.

Thanks
Weitianhua

[Alvin1Zhang]

Thanks for reporting and sorry for slow turnaround, the fix has been available at 8e4b919, feel free to reopen if the issue still happens. Thanks.