linux-kernel - n900 led compiler (was Re: [PATCH] Add LED pattern trigger)

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Date:	Sun, 5 Jan 2014 23:23:46 +0100
From:	Pavel Machek <pavel@....cz>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	pali.rohar@...il.com, sre@...g0.de, milo.kim@...com,
	linus.walleij@...aro.org
Cc:	Bryan Wu <cooloney@...il.com>, David Lang <david@...g.hm>,
	Joe Xue <lgxue@...mail.com>,
	"rpurdie@...ys.net" <rpurdie@...ys.net>,
	"rob@...dley.net" <rob@...dley.net>,
	"milo.kim@...com" <milo.kim@...com>,
	"linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: n900 led compiler (was Re: [PATCH] Add LED pattern trigger)

Hi!

> > IMHO, firstly we should take this trigger into kernel, most time it
> > works as a module. But we need to define a good interface between
> > kernel and user space.
> 
> You need the interface defined first. To do that it needs to reflect the
> actual hardware accelerated devices, and also to deal with resource
> management for those devices if necessary (eg if they can only manage one
> led of a set at a time).

Hardware can do quite a lot:

http://wiki.maemo.org/LED_patterns#Lysti_Format_Engine_Patterns_and_Commands

(and more).

I implemented compiler for it (should we put it into tools/ somewhere?)

https://gitorious.org/tui/tui/source/5b3f5cacf8e208d3ea50d6066e549940d85e55be:maemo/notcc.py

It can do quite a lot, including prime number computation. This uses
33% of program memory and only one of three execution units; but it
does not work, maybe I made mistake somewhere or maybe our kernel
can't take program this long. It only has 3 writable variables, which
is quite limiting.

start()
a = 1
next_number: a += 1
b = 1
next_divisor: b += 1
br = b
if (b==a) goto is_prime
c = 0
c = c+b
test_prime: if (c==a) goto not_prime
if (a<c) goto not_divisor
c = c+b
goto test_prime
not_divisor: goto next_divisor
not_prime: goto next_number
is_prime: b = 0
show_prime: c = 255
br = c
ramp_up_long(30,0)
c = 0
br = c
ramp_up_long(30,0)
b += 1
if (b == a) goto next_number2
goto show_prime
next_number2: goto next_number

> So the starting point has to be the hardware accelerated devices, whether
> you then support software emulation in kernel or user space is a follow
> on discussion. What the kernel/user API is also has to be a follow on

Well... this one is turing complete, and I have a compiler, but I
don't think it is good interface, either for library or kernel.

I believe series of RGB values might be good interface, maybe with
additional "want interpolation between these".
     		      	  	      	     	      	      	     Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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