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<h1>Compiling hello world program with the ZPU GCC toolchain</h1>
The ZPU comes with a standard GCC toolchain and an instruction set simulator. This allows compiling, running & debugging simple test programs. The Simulator has
some very basic peripherals defined: counter, timer interrupt and a debug output port.
<h1>Installation</h1>
<ol>
<li>Install Cygwin. http://www.cygwin.com
<li>Start Cygwin bash
<li>unzip zputoolchain.zip
<li>Add install/bin from zputoolchain.zip to PATH.<br>
export PATH=$PATH:<unzipdir>/install/bin
</ol>
<h1>Hello world example</h1>
The ZPU toolchain comes with newlib & libstdc++ support which means that many C/C++ programs can be compiled without modification.
<p>
<code>
zpu-elf-gcc -Os -zeta hello.c -o hello.elf -Wl,--relax -Wl,--gc-sections<br>
zpu-elf-size hello.elf<br>
</code>
<h1>Optimizing for size</h1>
The ZPU toolchain produces highly compact code.
<ol>
<li>Since the ZPU GCC toolchain supports standard ANSI C, it is easy to stumble across
functionality that takes up a lot of space. E.g. the standard printf() function is a beast. Some compilers drop e.g. floating point support
from the printf() function and thus boast a "smaller" printf() when in fact they have a non-standard printf(). newlib has a standard printf() function
and an alternative iprintf() function that works only on integers.
<li>The ZPU ships with default startup code that works across various configurations of the ZPU, so be warned that there is some overhead that will
not occurr in the final application(anywhere between 1-4kBytes).
<li>Compilation and linker options matter. The ZPU benefits greatly from the "-Wl,--relax -Wl,--gc-sections" options which is not used by
all architectures(e.g. GCC ARM does not implement/need -Wl,--relax).
</ol>
<h2>Small code example</h2>
<code>
zpu-elf-gcc -Os -abel smallstd.c -o smallstd.elf -Wl,--relax -Wl,--gc-sections<br>
zpu-elf-size small.elf<br>
<br>
$ zpu-elf-size small.elf<br>
text data bss dec hex filename<br>
2845 952 36 3833 ef9 small.elf<br>
<br>
</code>
<h2>Even smaller code example</h2>
If the ZPU implements the optional instructions, the RAM overhead can be reduced significantly.
<p>
<code>
zpu-elf-gcc -Os -abel crt0_phi.S small.c -o small.elf -Wl,--relax -Wl,--gc-sections -nostdlib <br>
zpu-elf-size small.elf<br>
<br>
$ zpu-elf-size small.elf<br>
text data bss dec hex filename<br>
56 8 0 64 40 small.elf<br>
<br>
</code>
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