Building eLua

If you decide to build your own eLua binary image (instead of downloading one) you need to download the source code (see here for details) and follow the platform specific eLua build instructions (provided for Linux and Windows) to setup your build environment. Then follow the instructions below to build your eLua binary image.

Configuring the build image

eLua has a very flexible build system that can be used to select the components that are going to be part of the eLua binary image and to set the compile time (static) configuration. To use it, you need to edit a single configuration file (platform_conf.h) located in the platform specific directory (src/platform/<platform name>/platform_conf.h). The configuration parameters are described in detail in the next paragraphs.

Configuring components

An eLua component is a feature that can be enabled to add functionality to eLua itself, without modifying its API (which is the part that the programmer uses to write eLua programs). An example of component configuration from platform_conf.h is given below:

// *****************************************************************************
// Define here what components you want for this platform

#define BUILD_TERM
#define BUILD_UIP
#define BUILD_DNS
#define BUILD_ADC
#define BUILD_RPC

The components that can be configured in eLua are:

Name Meaning
BUILD_XMODEM Define this to build support for XMODEM receive. If enabled, you can use the "recv" command from the shell to receive a Lua file (either source code or precompiled byte code) and run in on the target. Works only over RS-232 connections (although in theory it's possible to make it work over any kind of transport). To enable:
Static configuration data dependencies: CON_UART_ID, CON_UART_SPEED, CON_TIMER_ID
BUILD_SHELL This build the eLua shell (see using eLua for details on the shell). If the shell is not enabled, the code looks for a file called /rom/autorun.lua and executes it. If this file is not found, a regular Lua intepreter is started on the target.
To enable the shell over a serial connection:
To enable the shell over a TCP/IP connection:
BUILD_ROMFS Enable the eLua read-only filesystem. See the ROMFS documentation for details about using the ROM file system. To enable:
BUILD_MMCFS Enable the eLua SD/MMC FAT filesystem support. To enable:
Static configuration data dependencies: MMCFS_TICK_HZ, MMCFS_TICK_MS, MMCFS_CS_PORT, MMCFS_CS_PIN, MMCFS_SPI_NUM
BUILD_TERM Enable ANSI terminal support. It allows eLua to interact with terminals that support ANSI escape sequences (more details here). Currently it works only over RS-232 connections, although this is not a strict requirement. You need to enable this if you want to use the term module. To enable:
#define BUILD_TERM
Static configuration data dependencies: CON_UART_ID, CON_UART_SPEED, CON_TIMER_ID, TERM_LINES, TERM_COLS
BUILD_UIP Enable TCP/IP networking support. You need to enable this if you want to use the net module. Also, your platform must implement the uIP support functions (see the platform interface documentation for details). To enable:
#define BUILD_UIP
Static configuration data dependencies: ELUA_CONF_IPADDR0..3, ELUA_CONF_NETMASK0..3, ELUA_CONF_DEFGW0..3, ELUA_CONF_DNS0..3
BUILD_DHCPC If BUILD_UIP is enabled, you can enable this to include a DHCP client in the TCP/IP networking subsystem. To enable:
#define BUILD_UIP
BUILD_DNS If BUILD_UIP is enabled, you can enable this to include a minimal DNS resolver in the TCP/IP networking subsystem. To enable:
#define BUILD_UIP
#define BUILD_DNS
BUILD_CON_GENERIC Generic console support (details here). Enables console access (stdio/stdout/stderr) via a serial transport (currently RS-232, but others can be supported). Enable this if you want to use console input/output over your RS-232 connection. Don't enable this if you need console input/ouput over Ethernet (see the next option). To enable:
Static configuration data dependencies: CON_UART_ID, CON_UART_SPEED, CON_TIMER_ID
BUILD_CON_TCP Console input/output over TCP/IP connections only (details here). Use this if you want to use your eLua board over a telnet session. Don't enable this if you need console input/output over serial transports (see the previous option). To enable:
#define BUILD_UIP
BUILD_ADC Define this to build support for ADC peripherals. This must be enabled to use the adc module, or the adc platform interface. To enable:
#define BUILD_ADC
BUILD_RPC Define this to build support for LuaRPC. This must be enabled to use the rpc module. To enable:
#define BUILD_RPC
Static configuration data dependencies (ONLY if built with boot=luarpc): RPC_UART_ID, RPC_TIMER_ID

Configuring modules

You can also choose the modules that are going to be part of the eLua image. Unlike components, the modules have a direct impact on the eLua API, so choose them carefully. Disabling a module will save Flash space (and potentially RAM) but will also completely remove the possibility of using that module from eLua.

The modules included in the build are specified by the LUA_PLATFORM_LIBS_ROM macro. An example is given below:

  _ROM( AUXLIB_PIO, luaopen_pio, pio_map )\
  _ROM( AUXLIB_TMR, luaopen_tmr, tmr_map )\
  _ROM( AUXLIB_PD, luaopen_pd, pd_map )\
  _ROM( AUXLIB_UART, luaopen_uart, uart_map )\
  _ROM( AUXLIB_TERM, luaopen_term, term_map )\
  _ROM( AUXLIB_PWM, luaopen_pwm, pwm_map )\
  _ROM( AUXLIB_PACK, luaopen_pack, pack_map )\
  _ROM( AUXLIB_BIT, luaopen_bit, bit_map )\
  _ROM( AUXLIB_CPU, luaopen_cpu, cpu_map )\
   ROM( LUA_MATHLIBNAME, luaopen_math, math_map )

Each module is defined by a _ROM( module_name, module_init_function, module_map_array ) macro, where:

Please note that this notation is specific to LTR (the Lua Tiny RAM patch) and it's not the only way to specify the list of modules included in the build (although it is the most common one). Check the LTR section for more information about LTR.

For the full list of modules that can be enabled or disabled via platform_conf.h check the eLua reference manual.

Static configuration data

"Static configuration" refers to the compile-time configuration. Static configuration parameters are hard-coded in the firmware image and can't be changed at run-time. The table below lists the static configuration parameters and their semantics.

Name Meaning
Used to configure console input/output over UART. The specified UART id will be used for console input/output, at the specified speed. The data format is always 8N1 (8 data bits, no parity, 1 stop bits) at this point. The specified timer ID will be used for the console subsystem. These variables are also used by the XMODEM and TERM implementations.
Used to configure the ANSI terminal support (if enabled in the build). Used to specify (respectively) the number of lines and columns of the ANSI terminal.
Used by the TCP/IP implementation when the DHCP client is not enabled, or when it is enabled but can't be contacted. Specifies the IP address, network mask, default gateway and DNS server. Only needed if BUILD_UIP is enabled.
Specify the virtual timers configuration for the platform (refer to the timer module documentation for details). Define VTMR_NUM_TIMERS to 0 if this feature is not used.
Specify the rate at which SD/MMC timer function disk_timerproc() are being called by the platform. On most platforms MMCFS_TICK_HZ will match VTMR_FREQ_HZ. Only needed if MMCFS support is enabled.
Specify the port and pin to be used as chip select for MMCFS control of an SD/MMC card over SPI. Only needed if MMCFS support is enabled.
MMCFS_SPI_NUM Specify the SPI peripheral to be used by MMCFS. Only needed if MMCFS support is enabled.
PLATFORM_CPU_CONSTANTS If the cpu module is enabled, this defines a list of platform-specific constants (for example interrupt masks) that can be accessed using the cpu.<constant name> notation. Each constant name must be specified instead of a specific costruct (_C(<constant name>). For example:
After compilation, you can access these constants using cpu.INT_GPIOx. Note that the implementation of this feature needs virtually no RAM at all, so you can define as many constants as you want here.
BUF_ENABLE_ADC If the adc module is enabled, this controls whether or not the ADC will create a buffer so that more than one sample per channel can be held in a buffer before being returned through adc.getsample or adc.getsamples. If disabled, only one conversion result will be buffered. This option does NOT affect the behavior of the moving average filter.
ADC_BUF_SIZE If the adc module is enabled, and BUF_ENABLE_ADC is defined, this will define the default buffer length allocated at startup. This does not limit buffer sizes, it only defines the default length. Appropriate values range from BUF_SIZE_2 to BUF_SIZE_32768, with the numeric component at the end being in powers of 2.
ADC_BIT_RESOLUTION If the adc module is enabled, this will define the number of bits per adc conversion result. This is used to determine the maximum conversion value that can be returned by the ADC.
RPC_UART_ID If the rpc module is enabled and boot mode is set to luarpc, this selects which uart luarpc will listen on for incoming client connections.
RPC_TIMER_ID If the rpc module is enabled and boot mode is set to luarpc, this selects which timer will be used with the uart selected with RPC_UART_ID.
(version 0.7 or above) Configure the default (compile time) operation mode and memory limit of the emergency garbage collector (see here for details about the EGC patch). If not specified, EGC_INITIAL_MODE defaults to EGC_NOT_ACTIVE (emergency garbage collector disabled) and EGC_INITIAL_MEMLIMIT defaults to 0.

The rest of the static configuration data parameters are meant to be modified mainly by developers and thus they're not listed here.
One more thing you might want to configure for your build is the contents of the ROM file system. See the
ROMFS documentation for details on how to do this.

Invoking the build system

Once you have everything in place, all you have to do is to invoke the build system (scons) with the right arguments. This is a fairly easy step, although it might look intimidating because of the multitude of options than can be given to scons. They are used to fine tune the final image to your specific needs, but unless your needs are very special you won't need to modify them, so don't worry about the aparent complexity. The examples at the end of this section will show how easy it is to use the build system in practice.

$ scons 
[target=lua | lualong]
[cpu=at91sam7x256 | at91sam7x512 | i386 | str912fw44 | lm3s8962 |
lm3s6965 | lm3s6918 | lpc2888 | str711fr2 | at32uc3a0512 | stm32f103ze
[board=ek-lm3s8962 | ek-lm3s6965 | eagle-100 | str9-comstick | sam7-ex256 |
lpc-h2888 | mod711 | pc | atevk1100 | stm3210e-eval ]
[cpumode=arm | thumb]
[allocator = newlib | multiple | simple]
[toolchain = <toolchain name>]
[optram = 0 | 1]
[romfs = verbatim | compress | compile]

Your build target is specified by two paramters: cpu and board. "cpu" gives the name of your CPU, and "board" the name of the board. A board can be associated with more than one CPU. This allows the build system to be very flexible. You can use these two options together or separately, as shown below:

For board/CPU assignment look at the beginning of the SConstruct file (the platform_list array), it's self-explanatory.
The other options are as follows:

The output will be a file named elua_[target]_[cpu].elf (and also another file with the same name but ending in .bin/.hex if "prog" was specified for platforms that need these files for programming).
If you want the equivalent of a "make clean", invoke "scons" as shown above, but add a "-c" at the end of the command line. "scons -c" is also recommended after you reconfigure your build image, as scons seems to "overlook" the changes to these files on some occasions.

A few examples:

$ scons cpu=at91sam7x256 -c 

Clear previously built intermediate files.

$ scons cpu=at91sam7x256

Build eLua for the AT91SAM7X256 CPU. The board name is detected as sam7-ex256.

$ scons board=sam7-ex256

Build eLua for the SAM7-EX256 board. The CPU is detected as AT91SAM7X256.

$ scons board=sam7-ex256 cpu=at91sam7x512

Build eLua for the SAM7-EX256 board, but "overwrite" the default CPU. This is useful when you'd like to see how the specified board would behave (in terms of resources) with a different CPU (in the case of the SAM7-EX256 board it's possible to switch the on-board AT91SAM7X256 CPU for an AT91SAM7X512 which has the same pinout but comes with more Flash/RAM memory).

$ scons cpu=lpc2888 prog 

Build eLua for the lpc2888 CPU. The board name is detected as LPC-H2888. Also, the bin file required for target programming is generated. The allocator is automatically detected as "multiple".

$ scons cpu=lm3s8962 toolchain=codesourcery prog

Build the image for the Cortex LM3S8962 CPU, but use the CodeSourcery toolchain instead of the default toolchain (which is a "generic" ARM GCC toolchain, usually the one built by following the tutorials from this site.