In interrupt mode, writes can continue until can.ISR[TXFLL] generates an interrupt.
Messages can be continuously written to the TXFIFO until the TXFIFO is full. When the TXFIFO is full, the can.ISR[TXFLL] and can.SR[TXFLL] are set to 1. When the TXFIFO is empty, can.ISR[TXFEMP] is set to 1.