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In lugnet.robotics.rcx.legos, Mark Riley wrote:
> Also, if you're going to use inline assembly code, the compiler needs to be
> aware that variables can be changed by your code. One way is to declare the
> total variable as "volatile" like so:
>
> volatile unsigned char total;
Oh, I see. That's nifty. So a 'volatile' keyword ensures that it's reloaded
every time?
> FYI, I believe there are other ways (besides the volatile keyword) to tell the
> compiler about what your assembly code is doing, but I haven't delved that far
> into the docs yet (look under the __asm__ keyword for more info).
Which doc is this? The only ones I have are the BrickOS command reference (it's
a shorter HTML one), and the software manual from Hitachi.
> BTW, Kevin's suggestion of using the "-S" option with gcc is a good one, you can
> learn a lot about H8 assembly just by seeing what the C compiler produces (you
> can also learn what *not* to do! ;-) A simple way to get the source file is to
> type "make program.s" if your program is named program.c (I think you'll have to
> modify the Makefile if you're using C++, though).
Yeah, I'll check that out. I couldn't get it to work when I tried it at first,
but I'll give a more sustained attempt tonight.
One final thing is about accessing local variables. I didn't have a problem
using offsets on a global array, but what about a local one? I could change the
structure of my program so that all the vars that need to be accessed in this
way are globals, but it would be much more straight forward to do it this way.
Particularly since the specific procedure is part of a recursive function.
Mike
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Message has 1 Reply:
 | | Re: BrickOS Assembler
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| (...) Volatile tells the compiler that should assume the value can change without the compiler's knowledge. So yes, it gets reloaded every time. (...) To find this stuff, you need to read through documentation for GCC. It has been a few years since (...) (20 years ago, 21-Jan-04, to lugnet.robotics.rcx.legos)
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Message is in Reply To:
| | Re: BrickOS Assembler
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| (...) Glad to help! (...) However, it *does* work for bytes... See the program below. In your example program, you declared the "total" variable as an unsigned short (which is a 16-bit word), but accessed it using an 8-bit move instruction. Instead, (...) (20 years ago, 20-Jan-04, to lugnet.robotics.rcx.legos)
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