Not much info in the FCOM, is there. Maybe it's too much info for the non-engineer.
Two independent, identical stall management yaw damper (SMYD) computers determine when stall warning is required based upon:
alpha vane angle of attack outputs
ADIRU outputs
antiice controls
wing configurations
air/ground sensing
thrust
FMC outputs.
mach compensation
The SMYD computers provide outputs for all stall warning to include stick shaker and signals to the pitch limit indicator and airspeed displays and the GPWS windshear detection and alert.
I'd guess it comes from at least part of the list the SMYD uses for stall detection.