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Fri Nov 2 04:27:04 CET 2007

poke

i'm taking a day off.. so technically i'm not allowed to write in this
log. however, i got into PF today, and wrote a rant on the PF list
about mapping and partial evaluation.

maybe it's time to start writing poke, or nailing down the
requirements. the idea behind poke is to have a machine model for DSP
like tasks that can be setup (metaprogrammed) by say a scheme
system. the idea behind an application is this:

	1. a program is compiled for a VM.

	2. a new VM is instantiated (on a separate core/machine)

	3. the VM now runs in real-time: doing its own scheduling and
  	   stack based memory management, being able to communicate
  	   with its host system and other VMs

each VM is a linear tree stack/tree machine.


i'd like to do this without writing a single line of C code: have it
all generated. that's the only way to be serious about generating
*some* code.

it should have an s-expression interface with which it talks to a host
scheme system. this acts as message passing: no shared state
allowed. this syntax should have an easy extension for binary data.

it should be 'ready' for multiprocessing. what i mean with this is:
each processing core should be able to run a single machine instance,
so instances should be able to talk among each other in a simple way,
and there should be a schedulure available on the VMs to handle the
message passing.

i was thinking about a 'binary s-expression' approach to limit
inter-machine communication parsing overhead. data should still be
list-structured though, and word-aligned. for human interface, a
simple front-end could be constructed. arrays can be allowed for ease
of wrapping binary data.

internally, cons based lists are used for all representation. cdr
coding is used to be able to represent programs linearly. memory
inside the machine consists of stacks only. each machine uses a
limited set of data types, making re-use lists efficient.

aim for the highest possible gcc code generation efficiency: i see no
point in targeting anything else than gcc, so all extensions are
allowed. i just checked (see doc/gcc/tail.c) for tail call support and
it seems to work when putting functions in a single file. it also
works putting the functions in different files apparently. that's good
news. state passed: 3 stacks: DS/RS/AS

the target language should be a pointer-free safe language. this is
going to be a bit more difficult, probably have to split in safe /
unsafe parts.

the 'system' language and the 'inner loop' language are different and
should be treated as such. i probably should start with the latter and
build the control language as a layer on top. the former is a
forth-like language extended with linear tree memory and the latter is
a multi-in-multi-out language to be combined with combinators.


  1. all C code generated: need a generator.
  2. message passing interface using s-expressions.
  3. run-time memory (stacks/trees) is locally managed
  4. other (code) memory is static/readonly, loaded by host
  5. safe target language (from a certain point up)

so poke seems like a really straightforward extension to
forth. getting it compatible with PF will be quite something
though.. all this is pretty low priority. the only difficulty is how
to deal with pointers for optimizing the linear stack/tree data
structures. 'safe poke' :)



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