Re: Code Generation Question

["DuckE" <nospam_steved94@home.com>]

I have worked with one VME device that required 16 bit reads and writes, but
only returned/stored 8 bits at a time.  To make things even more difficult
the data was in the high order byte of the 16 bit word.

This device was one that was built in-house.  Apparently it was much easier
for the hardware designer to build it this way.

On an application developed using GCC on VxWorks I access 16 bit memory by
defining a pointer to a 16 bit value, assigning a memory address to the
pointer, and then accessing the memory through the pointer.

I hope this helps,

SteveD

"Charles H. Sampson" <claveman@cod.nosc.mil> wrote in message
news:98ug7e$9oj$1@newpoisson.nosc.mil...
>      This is not strictly an Ada issue but, since this group has one of
> the best signal to noise ratios in USENET, I'll post it here anyhow.  In
> my defense, it did arise in an Ada project that I'm currently working
> on.
>
>      Our project uses a heavily populated VME rack with a PowerPC as the
> CPU.  I certainly don't understand all of the VME arcania but it seems
> obvious to me that VME is at its root byte oriented.  One of the cards
> in the rack requires 16-bit reads and writes to its memory.  If you at-
> tempt an 8-bit read or write there is no indication of error; instead
> the board silently zeros the other byte of the 16-bit word.
>
>      This causes quite a bit of problem, as you might guess when you re-
> flect on it for a minute.  Whenever the module is modified (fortunately,
> it's now pretty stable), we have to investigate the code generated by
> the compiler to verify that there are no byte reads or writes to the
> board's memory.  If there are, we have to figure out a way to trick the
> compiler into not doing it.
>
>      I consider this wildly unreasonable.  My question is this: Are
> there compilers, for any language, that give the user the ability to
> subset the hardware instruction set used for a compilation?  I don't
> know of any and I've had experience with 20-30 compilers in my career.
> Other people, particularly those in academic settings, might have seen
> many more.
>
>                     Charlie
>
>
> --
> ******
>
>      For an email response, my user name is "sampson" and my host
> is "spawar.navy.mil".