11.4. A JTAG Traffic Generating Class

11.4.1. JtagLoggerSC Module Class Definition
11.4.2. JtagLoggerSC Module Class Implementation

In normal use, a debugger, such as GDB would be connected to the JTAG port. For demonstrating the interface, we use a stripped down JTAG logger class. This uses the debug interface to read the processor's next program counter SPR once per (modeled) second.

With the Or1ksim debug unit (see [2]), this requires the following steps.

Reset the JTAG interface
Shift DEBUG (0x8) into the JTAG instruction register.
Construct a JTAG data register to select module CPU0 so we can access its SPRs and shift that into the JTAG data register.
Construct a JTAG data register for the WRITE_COMMAND debug unit command, specifying that we wish to read the next program counter SPR and shift that into the JTAG data register.
Construct a JTAG data register for the GO_COMMAND debug unit command, to collect the value read from the next program counter SPR and shift that into the JTAG data register.

These last two steps are repeated with a wait of one second between, to give a regular report on the value of the next program counter.

11.3.3. Or1ksimJtagSC Module Class Implementation 11.4.1. JtagLoggerSC Module Class Definition