AM1808 PRU SUART INSMOD

I am using the PRU of AM1808,I have builded the suart_emu.ko.

NOW ,I found a qustion :

when the system start, the  soft uart  run ok,can receive and send data ;

but when the system run a time, the  soft uart  may can not receive and send data; 

so,I take steps:

modprobe -r suart_emu

insmod suart_emu.ko

Then ,I used the uart ,it run ok 

I do not know why?