The Virtual Series 2000 computer programming environment may be extended in two ways. First, the EasyCoder assembler may be extended with "Macro Libraries". Second, the system software may be simulated using "Virtual Runtimes".
When the assdembler encounters the (non-standard) "MAC" directive, it tries to load a java class using the single parameter. When the directive:
MAC <parameter>is encountered, a class is loaded with the name:
MacroLib<parameter>This class's constructor must accept an
Assemblerobject as it's only parameter. The assembler will then call the
boolean handles(String mac)method when it encounters a macro named in 'mac', and if return is 'true' then the assembler will call
int expand(String mac, String tag, String parms)to expand the macro.
Macro expansion typically calls back to the assembler's
int assemble(String line) method to add instructions to the program,
although it may also call the assembler's
and return -1 in case of errors.
Conventional ("native EasyCoder") macros are not (currently) possible due to lack of support for EasyCoder program libraries. This would also require support for job control commands in order to associate and assembler run with external libraries.
A virtual runtime is loaded when a program makes a branch to location '0-1' (the last character in memory). This is trapped by the virtual H2000 and an attempt is made to load a class named by the first parameter after the branch instruction. Additional paramaters are required by the runtime for initializing the program environment, but may vary between runtimes.
For example, a FORTRAN program always starts with:
B 0-1 DCW @FORTRAN@ DCW $FLIB DCW $FLIB1 R DCW $FLIB2Note the RM at the end of the last parameter, which is required. When the virtual H2000 services this branch/trap, it will load a class named
FORTRANRunTimeand call the constructor with the H2000 instance of the running system. The runtime constructor then initializes the communications area(s) in memory based on the additional parameters. This includes configuring traps so that the program may call into the runtime.
The runtime method
boolean doTrap() will be called at the
start of every instruction, and if returns 'true' then it means the trap
was serviced by the runtime (this only ends the system's search for the trap,
the runtime will have altered memory and/or registers, specifically SR, in
order to arrange for the correct program flow).
Since a runtime may persist in the system beyond the end of a program,
there must exist a
void reinit() method which is used to re-configure
an already-loaded runtime for a different program run.
Virtual runtimes are necessary due to the lack of any actual Honeywell systems program images. Without virtual runtimes, things like FORTRAN and MOD1 would be impractical/impossible.