> Hans-Peter Diettrich <drdiettri...@aol.com> wrote on Tue, 07 Feb 2012 > 09:12:53 +0100 > > > Base / Displacement consists of a 16 bit value, the first 4 bits enumerate a > > register, and the other 12 bits hold a displacement from 0 to 4095. The > > actual > > or Effective address for each storage operand is calculated as the unsigned > > addition of the value held in the base register to the displacement from the > > instruction itself. > > This reminds me of 8086 "real" mode, and 16 bit mode with (far) > addresses splitted into segment:offset. Using an 16 bit compiler and > syntax (near/far pointers and seg:off notation) would be easier to > support a segmented-memory architecture. I also don't see right now how > data structures > 4KB could be addressed, without subroutines to map > virtual into physical (here seg:off) addresses.
There are certain similarities, but System 360 onwards are true 32-bit processors. It's compilers, and there must be hunderds of them by now are 32-bit compilers. (Probably 64 bit too, I have never worked on the 64 bit types, so I don't know) Data structures -> see episode 5! > When I had a first look at the 8086 CPU, decades ago, I didn't > understand how to handle such a memory architecture in an compiler. Only > when I came across the Microsoft compilers and their memory models, I > saw how "hints" in the source code would allow an compiler to create > efficient machine code. But all these syntax externsions have been > stripped from nowadays compilers and languages, so that it will be very > hard to support such a dinosaur architecture in an 32/64 bit compiler. These systems have had had 32 bit compilers since the mid 1960's, it's not rocket science, just computer science. A version of C was implemented on 360 machines at Bell Labs long before it became a portable system. The architecture produces problems, but these are surmountable. I won't have answers to everything; I don't know enough (actually hardly anything) about the internals of the FreePascal code generator. I am confident enough in my abilities to know that these items are soluble; After all VS/Pascal solved them; GCC solved them (and there is a version of GCC available for 370 processors) etc _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
