> On Mar 26, 2015, at 17:26 , Joel Sherrill <joel.sherr...@oarcorp.com> wrote: > >> I think if 16 bit Harvard architecture (64K instruction / 64K data) targets >> are no longer supportable then 16 bit should be deprecated and then >> abandoned. If you can still do a lot with RTEMS in 128K then that useful >> subset of the code should be identified and kept 16 bit clean, that would be >> a good requirement on developers and that part of the code base. > >> That is, if anyone wants to do that, I currently use 4MB instruction / 4MB >> data as my minimal targets that can be comfortably extended during the >> support life time (I want TCP/IP and NFS as part of my minimum, your mileage >> will definitely vary). >> > The original target platform for RTEMS was 1MB RAM that was used for > everything. > I still think this is a very reasonable memory profile for most > applications. > > I am not sure if the 64K instruction/data is that useful but 16-bit > architectures are > not necessarily limited to 64K address spaces. We all remember the 8086 and > variants. The m32c has 24 bit address space. > > I don't know the requirements for what I used to frequently call > Tiny/RTEMS. > If you have a 20+ bit address space, then there isn't much of a code > size issue. > There will be combinations of code that just won't fit. I expect the new > TCP/IP > stack to be a casualty there. But the old TCP/IP stack worked quite well in > a 1MB environment and I would expect LWIP to do even better. > > So my focus is just on being 16-bit integer clean. I don't think we will > shrink > into the smallest AVR CPU models but something like an 8086 in large memory > model or an m32c shouldn't be an issue for most of RTEMS. > > But yes.. we should have some insight into which features are hopeless in > a 16-bit integer environment and maybe some idea of what is really too > small. >
We're talking about different things. I looked quickly at the M32C and see it has 24 bit address registers, and the 8086 is a nightmare. I think of 16 bit architectures as having 16 bit address and data, and not a mixed architecture with larger sized pointers (clean, un-aliased, pointers). I think you want to keep RTEMS 16 bit data clean, but not 16 bit address clean. Peter ----------------- Peter Dufault HD Associates, Inc. Software and System Engineering _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel
