nRF52832: Setting NRF_SDH_BLE_GATT_MAX_MTU_SIZE to more than 30 cause boot failure

[x_arrange]

Hello,

I'm trying to write BLE app that talks to Android phone. sometimes I need to set MTU more than 23 bytes so I decided to increase NRF_SDH_BLE_GATT_MAX_MTU_SIZE.

But as soon as I strt debugging app stucks in the middle of nowhere:

and do not run further.

I have feeling that ihas something to do with RAM, but may be I'm wrong.

Does anybody have experience with that?

[Amanda Hsieh]

Hi, 

When you change your MTU size you should also change the RAM allocation since the RAM usage for the stack will depend on certain things, like the GATT table size, MTU and TX-buffering settings, and similar.

If you modify NRF_SDH_BLE_GATT_MAX_MTU_SIZE you should adjust RAM start and RAM size for your project. 

Please see this post. 

-Amanda H.

[x_arrange]

Thanks, looks like I fodun how to change RAM start but it's still unclear how to calculate it.

If I have 0x200022f0 for  MAX_MTU=23, what is the value for 250 bytes?

[Amanda Hsieh]

Hi, 

You should check the log. Please enable the log in the sdk_config.h as

// <h> nRF_Log 

//==========================================================
// <e> NRF_LOG_BACKEND_RTT_ENABLED - nrf_log_backend_rtt - Log RTT backend
//==========================================================
#ifndef NRF_LOG_BACKEND_RTT_ENABLED
#define NRF_LOG_BACKEND_RTT_ENABLED 1
#endif

// <e> NRF_LOG_ENABLED - nrf_log - Logger
//==========================================================
#ifndef NRF_LOG_ENABLED
#define NRF_LOG_ENABLED 1
#endif

It will indicate the correct address as:

<warning> nrf_sdh_ble: Change the RAM start location from 0x2000XXXX to 0x2000XXXX.
<warning> nrf_sdh_ble: Maximum RAM size for application is 0xXXXX

Please modify the address as the log suggest.

If this cannot help you, please provide the log. 

-Amanda H. 

[x_arrange]

I already have log enabled but I don't see such messages.

What is the equation to calculate RAM offset?

[Amanda Hsieh]

There is no equation to calculate the RAM offset, but the log will indicate that.   

Could you provide the log?

-Amanda H.

[x_arrange]

I don't have any log - it just don't print it

[Amanda Hsieh]

If you couldn't see the log with Segger, enable UART log in sdk_config. 

// <e> NRF_LOG_BACKEND_UART_ENABLED - nrf_log_backend_uart - Log UART backend
//==========================================================
#ifndef NRF_LOG_BACKEND_UART_ENABLED
#define NRF_LOG_BACKEND_UART_ENABLED 1
#endif

Start a terminal emulator like PuTTY and connect to the used COM port with the following UART settings:

• Baud rate: 115.200
• 8 data bits
• 1 stop bit
• No parity
• HW flow control: None

If you still cannot see the log, please upload your project. 

-Amanda H.