Apparatus and method for determining a presence of a stored data frame in a random access memory independent of read and write clock domains

摘要

A network interface device includes a random access memory used as a transmit and receive buffer for transmission and reception of data frames between a host computer bus and a packet switched network. The network interface device includes read and write controllers for each of the transmit and receive buffers, where each write controller operates in a clock domain separate from the corresponding read controller. The memory management unit also includes a synchronization circuit that controls arbitration for accessing the random access memory between the read and write controllers. The synchronization circuit determines the presence of a stored frame in the random access memory by asynchronously comparing write counter and read counter values stored in gray code counters, where each counter is configured for changing a single bit of a counter value in response to an increment signal. Use of gray code counters enables asynchronous comparisons to be made between the two counter values, independent of the host computer bus clock domain and the network clock domain.