TCP provides a simple interface to the lower layers of the system. During
system initialization, the function tcp_init() has to
be called before any other TCP function is called. When the system is
running, the two timer functions tcp_fasttmr() and
tcp_slowtmr() must be called at regular intervals. The
tcp_fasttmr() should be called every
TCP_FAST_INTERVAL milliseconds (defined in tcp.h,
and currently 250ms) and
tcp_slowtmr() should be called every
TCP_SLOW_INTERVAL milliseconds, currently 500ms.