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diff --git a/doc/nimc.rst b/doc/nimc.rst index cc8d0875c..c1c418e01 100644 --- a/doc/nimc.rst +++ b/doc/nimc.rst @@ -542,26 +542,44 @@ for further information. Nim for embedded systems ======================== -The standard library can be avoided to a point where C code generation -for 16bit micro controllers is feasible. Use the `standalone`:idx: target -(``--os:standalone``) for a bare bones standard library that lacks any -OS features. +While the default Nim configuration is targeted for optimal performance on +modern PC hardware and operating systems with ample memory, it is very well +possible to run Nim code and a good part of the Nim standard libraries on small +embedded microprocessors with only a few kilobytes of memory. -To make the compiler output code for a 16bit target use the ``--cpu:avr`` -target. +A good start is to use the ``any`` operating target together with the +``malloc`` memory allocator and the ``arc`` garbage collector. For example: -For example, to generate code for an `AVR`:idx: processor use this command:: +``nim c --os:any --gc:arc -d:useMalloc [...] x.nim`` - nim c --cpu:avr --os:standalone --genScript x.nim +- ``--gc:arc`` will enable the reference counting memory management instead + of the default garbage collector. This enables Nim to use heap memory which + is required for strings and seqs, for example. -For the ``standalone`` target one needs to provide -a file ``panicoverride.nim``. -See ``tests/manyloc/standalone/panicoverride.nim`` for an example -implementation. Additionally, users should specify the -amount of heap space to use with the ``-d:StandaloneHeapSize=<size>`` -command line switch. Note that the total heap size will be -``<size> * sizeof(float64)``. +- The ``--os:any`` target makes sure Nim does not depend on any specific + operating system primitives. Your platform should support only some basic + ANSI C library ``stdlib`` and ``stdio`` functions which should be available + on almost any platform. +- The ``-d:useMalloc`` option configures Nim to use only the standard C memory + manage primitives ``malloc()``, ``free()``, ``realloc()``. + +If your platform does not provide these functions it should be trivial to +provide an implementation for them and link these to your program. + +For targets with very restricted memory, it might be beneficial to pass some +additional flags to both the Nim compiler and the C compiler and/or linker +to optimize the build for size. For example, the following flags can be used +when targeting a gcc compiler: + +``--opt:size --passC:-flto --passL:-flto`` + +The ``--opt:size`` flag instructs Nim to optimize code generation for small +size (with the help of the C compiler), the ``flto`` flags enable link-time +optimization in the compiler and linker. + +Check the `Cross compilation` section for instructions how to compile the +program for your target. Nim for realtime systems ======================== |