[quote user="Li Wen"]
Is that because of the UART speed? Did you configure the UART at 57600bps?
[/quote]
No, it is not. I have configured the UART at 115,200 and I'm also using SPI at 4 MHz (which is slightly faster). Same effective notification speed. Some of it has to do with the extra processing done by the slow core, and some of it by the fact that most data packets go alone, not two or three every interval.