ESP32-S3 stuck at 3 simultaneous connections despite CONFIG_BT_NIMBLE_MAX_CONNECTIONS=4

[HerveGagnon]

Hello @h2zero,

I’m running NimBLE-Arduino on an ESP32-S3 (PlatformIO, Arduino framework) and I’m trying to support 5 simultaneous BLE peripheral connections (4 actuator nodes + 1 level node).

Here is my code, here is what I tried, here is the output.

The problem is that the server consistently stops accepting connections after the 3rd connection.

Runtime output shows:

NimBLE max connections = 3
NIMBLE_MAX_CONNECTIONS=3

When the 3rd client connects:

BLE connected handle=3
Connections=3
E NimBLEAdvertising: Error enabling advertising; rc=6
Restart advertising result=0 Advertising=0

After that, advertising stops and no additional clients can connect.

Things I’ve already tried:

1. Created my own nimconfig.h:

#define CONFIG_BT_NIMBLE_MAX_CONNECTIONS 4
#define CONFIG_BT_NIMBLE_MAX_BONDS 3
#define CONFIG_BT_NIMBLE_MAX_CCCDS 9
#define CONFIG_BT_NIMBLE_ATT_PREFERRED_MTU 100

#define MYNEWT_VAL_BLE_MAX_CONNECTIONS 4
#define MYNEWT_VAL_BLE_ATT_PREFERRED_MTU 100
#define MYNEWT_VAL_BLE_MAX_CCCDS 9

2. Included it before NimBLEDevice.h:

#include “nimconfig.h”
#include <NimBLEDevice.h>

3. Added runtime diagnostics:

Serial.printf(“NIMBLE_MAX_CONNECTIONS=%d\n”, NIMBLE_MAX_CONNECTIONS);

Result is still:

NIMBLE_MAX_CONNECTIONS=3

4. Grep results show NimBLE-Arduino’s internal nimconfig.h still contains:

#define CONFIG_BT_NIMBLE_MAX_CONNECTIONS 3

The final system requires:

• 4 Arduino Nano 33 BLE clients (actuators)
• 1 Arduino Nano 33 BLE client (level sensor)

All connect to a single ESP32-S3 NimBLE server.

Question:

What is the correct way to override CONFIG_BT_NIMBLE_MAX_CONNECTIONS when using NimBLE-Arduino under PlatformIO on ESP32-S3?

Should this be done through build_flags, sdkconfig.defaults, a custom nimconfig.h, or by modifying the library’s nimconfig.h directly?

Also, are there any ESP32-S3-specific limits that would prevent 4 or 5 simultaneous peripheral connections?

Thanks.

[h2zero]

If you are using platformio I suggest these values to be set in the build flags,.