The quality of service (QoS) requirements limit the probability of losing received packets to 1%. How do we determine whether the design has enough memory to satisfy this requirement? To answer this question we need to model behaviors such as packet loss from the receive buffer and its relation to the size of the shared memory.
Figure 5 shows the SimEvents model of this system. The upper part of the model describes a receive buffer, where messages arrive from an I/O device such as a universal asynchronous receiver transmitter (UART). The lower part of the model describes a transmit buffer, where messages wait before transmission.
Both receive and transmit buffers model the following processes:
Generation of variable-size messages: The traffic-generation process generates messages with variable size.
Regulation of the messages that cannot be stored in the buffer: When a buffer size crosses a user-defined threshold, the Message Flow Regulation subsystems begin to drop incoming messages.
Storage of messages in a buffer: The receive and transmit buffers share memory, and the receive buffer is given a preference. The memory available for transmitting messages is limited to that which is unused by the receive buffer.
Service of messages: The block labeled Rx Message Server models the delay in forwarding messages over the I/O bus that connects to other components. The block labeled Tx Message Server models the delay in transmitting messages.