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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Strict//EN">
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<html><head>
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<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
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<meta http-equiv="Content-Language" content="en-us"><title>Porting eLua</title>
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<link rel="stylesheet" type="text/css" href="../style.css"></head>
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<body style="background-color: rgb(255, 255, 255);">
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<h3>Porting eLua</h3>
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<p>So, you realized how cool <b>eLua</b> is :), and you'd like to give it a try. Unfortunately, <b>eLua</b> doesn't have a port on your CPU of choice.
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The solution is simple: write the port yourself. This might seem as a daunting task at first, but it's actually easier than it sounds. <b>eLua</b> was
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designed to make the task of implementing new ports as easy and intuitive as possible. This section gives an overview of the porting process. It's not
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an exhaustive guide, but it should be enough to point you in the right direction. Before diving into this, it's highly recommended that you take a look
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at the <a href="elua_arch.html">eLua architecture page</a>. </p>
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<h3>Prerequisites</h3>
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<p>Before starting to work on the port, make sure that:
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<ul>
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<li>your CPU has enough resources to run <b>eLua</b>. A very rough estimation (based on ARM Thumb code only) is that you'd need at least 256k
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of program memory and 32k of RAM for a complete <b>eLua</b> image, and 128k of program memory for a basic image. It's possible to run <b>eLua</b> in
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less than 32k of RAM (especially when <a href="arch_ltr.html">LTR</a> is enabled), but you'll probably run out of memory fast.
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64k of RAM (or more) is recommended.</li>
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<li><a target="_blank" href="http://sourceware.org/newlib">Newlib</a> can be compiled for your CPU. <b>eLua</b> depends on Newlib currently
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(although this limitation will be eliminated in a future version), so if Newlib is not available for your CPU, you're out of luck. </li>
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<li>you have a C compiler for your target. Ideally you'd use GCC, but if this isn't possible other compilers might work as well. Keep in mind that
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<a href="arch_ltr.html">LTR</a> needs a C99 C compiler (or at least a partially C99 compliant C compiler than supports C99-style union initialization).
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</li>
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</ul></p>
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<p>If all of the above are true, you should continue reading this document to bring your port to life. If not, we're sorry, but (at least at this point)
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<b>eLua</b> can't be ported to your CPU.</p>
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<h3>Overall structure of a port</h3>
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<p><b>eLua</b> uses the notion of <b>platform</b> to denote a group of <b>CPUs</b> that share the same core structure, although their specific silicon
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implementation might differ in terms of intergrated peripherals, internal memory and other such attributes. An <b>eLua</b> port implements one or
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more CPUs from a given platform. For example, the <b>lm3s port</b> of <b>eLua</b> runs on LM3S8962, LM3S6965 and LM3S6918 CPUs, all of them part of the
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<b>lm3s</b> platform (reffer to <a href="status.html">the status page</a> for a full list of platforms and CPUs on which <b>eLua</b> runs). </p>
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<p>All the source files specific to a platform/port reside in a subdirectory of <i>src/platform</i> that has the same name as the platform (for <b>lm3s</b>
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it would be <i>src/platform/lm3s</i>, for example). Each such platform-specific subdirectory must contain at least these files:</p>
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<ul>
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<li><b>type.h</b>: this defines the "specific data types", which are integer types with a specific size (see <a href="arch_coding.html">coding style</a>
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for details. An example from the <b>i386</b> platform:
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<p><pre><code>typedef unsigned char u8;
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typedef signed char s8;
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typedef unsigned short u16;
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typedef signed short s16;
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typedef unsigned long u32;
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typedef signed long s32;
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typedef unsigned long long u64;
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typedef signed long long s64;</code></pre></p>
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</li>
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<li><b>conf.py</b>: this is the platform specific build configuration file, used by the <a href="building.html">build system</a> for a number of purposes:
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<ul>
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<li>to get the list of platform-specific files that will be compiled in the <b>eLua</b> image. They are exported in the <i>specific_files</i> string,
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separated by spaces, and must be prepended with the relative path to the platform subdirectory. An example from the <b>i386</b> platform:
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<p><pre><code>specific_files = "boot.s common.c descriptor_tables.c gdt.s interrupt.s isr.c kb.c monitor.c timer.c platform.c"
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# Prepend with path
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specific_files = " ".join( [ "src/platform/%s/%s" % ( platform, f ) for f in specific_files.split() ] )</code></pre></p>
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</li>
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<li>to get the full command lines of the different toolchain utilities (linker, assembler, compiler) used to compile <b>eLua</b>. They must be declared
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inside the <i>tools</i> variable, in a separate dictinoary which key is the same as the platform name, and with specific names for each tool in turn:
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<b>cccom</b> for the compiler, <b>linkcom</b> for the linker and <b>ascom</b> for the assembler.
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For example, this is how the <i>tools</i> variable is defined for the <b>i386</b> platform:
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<p><pre><code># Toolset data
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tools[ 'i386' ] = {}
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tools[ 'i386' ][ 'cccom' ] = "%s %s %s -march=i386 -mfpmath=387 -m32 -ffunction-sections -fdata-sections -fno-builtin -fno-stack-protector %s -Wall -c $SOURCE -o $TARGET" % ( toolset[ 'compile' ], opt, local_include, cdefs )
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tools[ 'i386' ][ 'linkcom' ] = "%s -nostartfiles -nostdlib -march=i386 -mfpmath=387 -m32 -T %s -Wl,--gc-sections -Wl,-e,start -Wl,--allow-multiple-definition -o $TARGET $SOURCES -lc -lgcc -lm %s" % ( toolset[ 'compile' ], ldscript, local_libs )
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tools[ 'i386' ][ 'ascom' ] = "%s -felf $SOURCE" % toolset[ 'asm' ]</code></pre></p>
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Note how the definition of <b>tools</b> uses the definition of <b>toolset</b>, a dictionary with the names of the tools in the current toolchain. This
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is also part of the <b>eLua</b> build system and is documented <a href="toolchains.html">here</a>.</li>
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<li>to get the name of a <b>programmning function</b> which receives the name of the <b>eLua</b> executable file (the result of the build step) and
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produces a file suitable for programming on the corresponding hardware platform. The name of this function should also be set in the <i>tools</i>
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dictionary, as shown below (example taken from the <b>str7</b> platform):
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<p><pre><code># Programming function for STR7
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def progfunc_str7( target, source, env ):
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outname = output + ".elf"
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os.system( "%s %s" % ( toolset[ 'size' ], outname ) )
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print "Generating binary image..."
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os.system( "%s -O binary %s %s.bin" % ( toolset[ 'bin' ], outname, output ) )
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tools[ 'str7' ][ 'progfunc' ] = progfunc_str7</code></pre></p>
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Note, once again, how this function uses the same <i>toolset</i> variable mentioned in the previous paragraph.
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</li>
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</ul>
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</li>
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<li><b>stacks.h</b>: by convention, the stack(s) size(s) used in the system are declared in this file. An example taken from the <b>at91sam7x</b> platform is given below:
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<p><pre><code>#define STACK_SIZE_USR 2048
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#define STACK_SIZE_IRQ 64
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#define STACK_SIZE_TOTAL ( STACK_SIZE_USR + STACK_SIZE_IRQ )</code></pre></p></li>
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<li><b>platform.c</b>: by convention, the <a href="">##platform interface</a> is implemented in this file. It also contains the platform-specific
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initialization function (<i>platform_init</i>, see the description of the <a href="elua_arch.html#boot">eLua boot process</a> for details).</li>
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<li><b>platform_conf.h</b>
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</ul><p>
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<p>
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</p>
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<h3>Prerequisites</h3>
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<p>The very first thing to do before starting a new port is to verify if you can use one of the already existing <b>platforms</b>. A <b>platform</b> groups
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CPUs that share the same core structure, although their specific silicon implementation might differ in terms of integrated peripherals, internal memory,
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package size and other such attributes. For a list of ports currently supported by <b>eLua</b> check the <a href="status.html">status page</a>. If you
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find
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</p>
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</body></html>
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