Retro1.org codex

GPR                                                            DEBUG subcommand

Use the GPR subcommand to display the contents of one or more general registers
at the console.

The format of the GPR subcommand is:
+----------+------------------------------------------------------------------+
| GPR      | reg1 [reg2]                                                      |
+----------+------------------------------------------------------------------+

where:

reg1     is a decimal number (from 0-15 inclusive) indicating the first or only
         general register whose contents are to be displayed.

reg2     is a decimal number (from 0-15 inclusive) indicating the last general
         register whose contents are to be displayed.  "reg2" must be larger
         than "reg1."