Nordic Thingy 52 FW Source Code Query

Hello,

I have a question related to the Nordic Thingy 52 FW source code that's been posted at https://github.com/NordicSemiconductor/Nordic-Thingy52-FW/blob/master/source/ble_services/ble_tms.c

I was just wondering if I could be pointed to the file that contains the definition of the sd_ble_gatts_hvx() function that is called at line 1164. 

For a bit of context, what I'm trying to achieve is to track the flow of the 9-axis points that are assigned in the file https://github.com/NordicSemiconductor/Nordic-Thingy52-FW/blob/master/source/modules/m_motion.c from lines 351-361. The end of that function results in a call to the ble_tms_raw_set function in ble_tms.c (see first link). Additionally, I tried tracking down the chain of #include files to find out where the definition of the function resides, but for some reason I'm unable to find certain header files in the github repo. I'm thinking that the definition of the function I'm looking for could be in those files that I'm unable to access, but I'm unsure as to what the case actually is.

Any help with this matter would be much appreciated! Thank you.