This articles was published on 2012-06-02
Due to the reason that I paused for a moment my activities on improving the testing platform for mruby (the reason is already clarified *happy*) I took a look at some hardware which was available at my place. I found a small embedded device with the following specification:
Atheros SoC AR9331, this means a 400Mhz MIPS CPU, with USB, Ethernet and 802.11n interface. Additionally there is 4MB Flash available on the device:
Porting mruby to this little device consisted of three steps
I’m a huge fan of OpenWRT. Many people know that OpenWRT is an awesome embedded Linux Distribution. But what many people don’t know is, that OpenWRT has an awesome implementation of a Cross Compiling toolchain. They didn’t really invented something by themselves but they build up a nice environment in which you can just cross-compile stuff even if you don’t want to use it on their platform. Writing an OpenWRT specific Makefile is as easy as this:
include $(TOPDIR)/rules.mk include $(INCLUDE_DIR)/kernel.mk PKG_NAME:=mruby PKG_REV:=b2d0f22dee87651bca4e16e287cab61dc303db19 PKG_VERSION:=0.1 PKG_RELEASE:=1 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2 PKG_SOURCE_SUBDIR:=$(PKG_NAME)-$(PKG_VERSION) PKG_SOURCE_PROTO:=git PKG_SOURCE_URL:=git://github.com/mruby/mruby.git PKG_SOURCE_VERSION:=$(PKG_REV) include $(INCLUDE_DIR)/package.mk define Package/mruby SECTION:=language CATEGORY:=Base system TITLE:=Embeddable Ruby Language URL:=http://github.com/mruby/mruby endef define Package/mruby/description mruby is an embeddable version of the Ruby Programming language. endef define Package/mruby/install $(INSTALL_DIR) $(1)/usr/sbin $(INSTALL_BIN) $(PKG_BUILD_DIR)/bin/mruby $(1)/usr/sbin endef $(eval $(call BuildPackage,mruby))
There is one small trap in the mruby compile process. Parts of mruby are written in Ruby itself. During the compilation process a tool called mrbc will be compiled which then compiles all Ruby files under mrblib. The result is some C-Code which then will be again compiled to the final object. The problem for cross-compiling is now that we need to compile mrbc for the host machine but the result of mrbc has to be compiled for the target machine. Our cmake branch of mruby has already some features to support that but the default Makefiles aren’t able to do that. Due to the reason that I don’t want to mess around with cmake inside of the OpenWRT toolchain I decided to just compile the mrbc static on my machine up-front. Then I deleted everything except the bin/mrbc file. Afterwards I could bootstrap the complete compile. The Makefiles are smart enough to recognize that they don’t need to compile mrbc again. So they just skip that process and they use my host compatible version of mrbc to prepare all Ruby files for the target machine.
matz is using LL inside of his Makefiles to prepare the final libmruby. I’m not sure if this is very standard conform. Nevertheless my default toolchain doesn’t recognize this abbreviation. So I had to change the Makefile there too.
As you will see, compiling for MIPS in a proper toolchain and with a little bit of stripping you can bring down the mruby binary to a size of 429K. I bet I can make it even smaller in the future:
root@OpenWrt:~# ls -lah /usr/bin/mruby -rwxr-xr-x 1 root root 429.4K Jan 1 00:05 /usr/bin/mruby root@OpenWrt:~# uname -a Linux OpenWrt 3.2.5 #3 Wed Feb 15 13:46:20 SGT 2012 mips GNU/Linux root@OpenWrt:~# cat /proc/cpuinfo system type : Atheros AR9330 rev 1 machine : TP-LINK TL-WR703N v1 processor : 0 cpu model : MIPS 24Kc V7.4 BogoMIPS : 265.42 wait instruction : yes microsecond timers : yes tlb_entries : 16 extra interrupt vector : yes hardware watchpoint : yes, count: 4, address/irw mask: [0x0000, 0x0060, 0x03c0, 0x0280] ASEs implemented : mips16 shadow register sets : 1 kscratch registers : 0 core : 0 VCED exceptions : not available VCEI exceptions : not available root@OpenWrt:~# mruby -v mruby - Embeddable Ruby Copyright (c) 2010-2012 mruby developers puts "Hello World" NODE_SCOPE: local variables: NODE_BEGIN: NODE_CALL: NODE_SELF method='puts' (276) args: NODE_STR "Hello World" len 11 irep 110 nregs=4 nlocals=2 pools=1 syms=1 000 OP_LOADSELF R2 001 OP_STRING R3 'Hello World' 002 OP_LOADNIL R4 003 OP_SEND R2 'puts' 1 004 OP_STOP Hello World root@OpenWrt:~#