Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Keil/AT32F407xx_v2/CAN1/RF1#0x0
Receive FIFO 1 register
Receive FIFO 1 message num
Receive FIFO 1 full flag
Receive FIFO 1 overflow flag
Receive FIFO 1 release
https://github.com/cmsis-svd/cmsis-svd-data