SSI interface - need good programming advice

I need to use 3 (of the 4 available on the RCM3000) SSI interfaces and I want to use the SSI.lib but I have the following doubts:
1-How do you calculate the clock frequency? According to TN200 the time constant register should be definded as: 4x(N+1) but there is no explanation anywhere of how it works.
2-How do you setup different clock frequencies for every port?
3-Do you need to run the sp_init() function for every port everytime you are going to read/write a different SSI device?