UDP Block with blocking mode

Hi,

I want to use the UDP blocks, that you can download here: http://www.mathworks.com/matlabcentral/fileexchange/12021-udpip

They both work fine, but I want the receiving block to wait for incoming data until the simulation will proceed (e.g. if I pause the send-block). I looked up the C-code and found out, that recvfrom() should be able to block, i.e. it should wait for incoming data before it proceed. But it doesn't and I'm not familiar with C-code, so I have no clue why.

Any suggestions?

(I'm using Matlab 6.5)