hardfault on an sd_ble_gatts_hvx call in sdk 14.2.0

Question

Referencing another trouble ticket 
 https://devzone.nordicsemi.com/f/nordic-q-a/22621/hardfault-on-an-sd_ble_gatts_hvx-call-in-sdk12-3 
 I am experiencing the same issue as listed in the reference issue. Using SDK 14.2.0, FreeRTOS project built off of FreeRTOS example. 
 Battery service can send notifications just fine, but my custom service cannot. I am using the FreeRTOS xTimer to send out a 20 byte packet on a periodic base. Call to this function fails on first call. I have seen other that have had the same issue, or similar, and perhaps it is a priorities issue but I cannot fix this. 
 Cheers

Susheel Nuguru · Answer

Hi Sensorian, 
 If it is exactly the SVC call you mentioned that causes the hardfault , then it most likely looks like the issue with priority settings in your project or calling SVC at at the wrong place 
 As you can see that for nRF52 devices using our BLE softdevice, the SVC priority is set to 4. If you are calling any sd_xxx functions from a context that has interrupt priority set to 4 or lower in number (3,2 1 or 0) then the call would hardfault. 
 Also FreeRTOS uses BASEPRI/PRIMASK (nrf52/nrf51) register to mask interrupts to execute code in critical section. You cannot call any softdevice API in this critical region of code. 
 I would see no other issue as many customers are using FreeRTOS to implelment their custom services without any issues. 
 BTW, new SDK release SDk15 have upgraded FreeRTOS kernel from 8.0.0 to 10.0.0, may be you would like to use it (not to solve this problem, but to get benefited from the newer RTOS version)