Subject:
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Re: anyone know how to check free space on RCX?
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Newsgroups:
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lugnet.robotics.rcx.legos
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Date:
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Fri, 12 Jul 2002 02:40:14 GMT
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Viewed:
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2335 times
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On Thu, 11 Jul 2002, Joseph Woolley wrote:
> That is very interesting Jason. It is interesting that mm_free_mem()
> returns a 16bit value using a 32bit return code. Both int and long are
> 32bit value on most computers/compilers these days; short would be a 16bit
> value; and char would be an 8bit value. Maybe mm_free_mem() should return
> an unsigned short instead.
int is defined as the natural width of the processor, which on a 16-bit
processor is 16 bits. longs are 64 bits on some machines as well, so you
can't assume it is always 32 bits -- if your code cares, use sizeof.
> I have used lcd_int and cputw to display 32bit values (although I am not
> sure if lcd_int displays the value in hex or dec. I may be wrong about it
> displaying hex). So lcd_int is looking only at the first word, whereas
> cputw is looking at the second word.
>
> Thank you for pointing this out! I guess the next step is to check the
> instruction timing for using 16bit values vs 32bit values. If the
> instruction timing is roughly the same, it may be worth updating some of the
> code to use unsigned short instead of int or unsigned int. On the other
> hand, if a new RCX is released with more memory, we could run into problems.
32-bit math on the H8 is substantially slower than 16-bit as it requires
multiple instructions. Any new version of the RCX that added more memory
would be so different that worrying about portability to a hypothetical
machine is wasted effort.
John A. Tamplin jat@jaet.org
770/436-5387 HOME 4116 Manson Ave
770/431-9459 FAX Smyrna, GA 30082-3723
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