b/w reflective mode for monitor

[Mitch Bradley]

David W Hogg wrote:
> Perhaps this is a question for hardware folks, not devel folks, but
> could someone out there tell me if the reflective, b/w mode for the
> monitor will be 8-bit greyscale or 1-bit on-off pixels?  I am writing
> an application for the laptop, but it is *essential* that it run
> completely in the reflective mode if that is possible; I need to know
> if I can use "greys" or only strict "black" and "white".
It is greyscale, but not a simple 8 bit-per-pixel mode.  I don't 
completely understand all the details, but I do know that if you are in 
monochrome mode and you write color values of different luminance, you 
see different shades of gray.  For example, you can generate a 
monotonically increasing brightness ramp as follows:

  a) Set the display controller to RGB565 mode (the mode that we use in 
most cases)
  b) With the R and B components set to 0, increment G from 0 to 63
  c) With G at 63, increment B from 0 to 31
  d) With G at 63 and B at 31, increment R from 0 to 31.

That gives you 128 distinct grays, which my eye can distinguish for the 
most part (although the darkest 10 or so look essentially black to me).

I presume that one could improve on that by using more subtle combinations.
>
> Also, are there *software* handles for the reflective vs transmissive
> modes, or is that always controlled by hardware and/or the user?
Both the backlight and the color/monochrome modes can be controlled in 
software.

You can convince yourself of all these assertions with simple tests from 
the firmware (it helps to use a recent firmware release like 
http://wiki.laptop.org/go/OLPC_Firmware_Q2B61 , because the logo in 
versions Q2B34 and later is multicolored, so it shows the different 
shades of gray).

ok  stdout @ iselect
ok 0 set-color
ok 0 bright!

The "set-color" command goes into monochrome mode, while the "bright!" 
command turns the backlight all the way down.

There are ways to do this from Linux, but I don't have the details handy.
>
> Thanks very much in advance for any help you can give.
>
> Hogg
>
> ps. If you want to know *why* I need to work in the reflective mode:
> my application is for backyard/schoolyard astronomy and we must
> maintain dark adaptation.  See
>   http://howdy.physics.nyu.edu/index.php/OLPC_planetarium
>
> pps. Hey you Media Lab types:  I was Lego Lab 1989-1992.