The terminal provides a SystemC buffer to model the Rx and a port to model the Tx pins of a serial connection. The visualization is provided by a Linux xterm running in a child process, with communication through a pseudo-TTY^[5].

Two SystemC processes are used, one a method waiting for bytes from the UART in the Rx buffer, the other a thread waiting for bytes from the xterm. When bytes are received in the Rx buffer, they are written to the xterm. When bytes are received from the xterm they are written to the Tx port. The key interfaces are shown in Figure 7.3.

Figure 7.3.  SystemC terminal model using a xterm child process.

The difficulty is in waiting for the xterm. As described above, reading from the pseudo-TTY is an operating system call, and does not use the SystemC wait, so the thread will not yield and the simulation will block. Instead the pseudo-TTY is set up to use asynchronous I/O, which will cause a Linux SIGIO to be raised whenever data is available to read. The event handler for SIGIO will then notify a SystemC event, and it is this SystemC event on which the thread can safely wait.