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> Ok, thanks. I'll try everything else first, then try this if I get
> desperate. The main thing I hit a wall with was when I switched to
> floating-point, which increased my .lx filesize by about 2k, so if I go
> back to fixed-point, turn sound off in config.h, and watch my stack sizes
> in my execi I'll probably be ok. If I do happen to try -Os, I'll certainly
> write back and say how it went.
Having written a few embedded-systems compilers, I must say that using
floating point on an 8-bit chip like the H8 is generally considered crazy.
The values eat memory, and the libraries drawn in can get really large (at
least for a production compiler that has to support full ANSI).
The H8/300 is a mightly little chip: 16 Mhz and 32kB of RAM is a VERY
POWERFUL computer, far better than my first home computer back in 1985. But
floating point has no place here. Try to approximate using integers.
A problem is that gcc has a poor linker that only resolves on a module
level, and not a per-function basis. This means that if any function in a
certain file is needed, the code for the whole file will be linked in.
In general, it is a good idea on smaller chips to:
* Use 8-bit variables, i.e. char and unsigned char, wherever possible.
* Avoid pointers.
* Avoid function pointers.
* Avoid dynamic memory allocation.
* Avoid floating point like it was the black plague. Including floating-
point constants.
* Send large data by reference rather than by copy (pointers to structs)
* Set the compiler to maximal size optimization. You do not have a speed
problem normally, the outside world is far slower than your code.
* Use the minimal number of tasks, since the tasking model used in LegOS is
quite wasteful of the stack (one stack per task, "while(1)" task bodies,
is a very bad way to use data memory).
/jakob
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Message is in Reply To:
 | | Re: Memory Usage
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| (...) Ok, thanks. I'll try everything else first, then try this if I get desperate. The main thing I hit a wall with was when I switched to floating-point, which increased my .lx filesize by about 2k, so if I go back to fixed-point, turn sound off (...) (24 years ago, 15-Oct-00, to lugnet.robotics.rcx.legos)
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