Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Atmel/ATSAM3S1C/TC1/QISR#0x0
QDEC Interrupt Status Register
InDeX
DIRection CHanGe
Quadrature ERRor
DIRection
https://github.com/cmsis-svd/cmsis-svd-data