[GEM Development] More driver updates

[John Elliott]

  I've now done quite a big update to my FreeGEM drivers page at
<http://www.seasip.info/Gem/drivers.html>:

- The 256-colour driver has been updated with some bugfixes. It now
 shouldn't get collywobbles if you move the mouse to the extreme bottom or
 extreme right of the screen. I've also increased the sizes of some buffers 
 and removed some left-over OUT instructions which may have caused crashes.

- There are now twenty-one drivers with all the latest FreeGEM codepage
support. I've divided them into five categories:

  * The 256-colour driver, which is sui generis.

  * Pack 1, "preferred" drivers - basically FreeGEM versions of the three
    ViewMAX/2 drivers. SDUNI9 supports EGA and VGA, SDCAT9 supports CGA and
    the "AT&T" 640x400 mode, and SDHRC9 supports Hercules.

  * Pack 2, "alternative" drivers - any other drivers for standard
    hardware. This includes things like a reverse-video CGA driver 
    (inspired by Jaroslaw Binczaowski), a 640x200 EGA driver (in case you've
    got an EGA with a CGA monitor), and the old favourite SDPSC9.

  * Pack 3 covers less-common hardware. It's got three drivers - one for
    the AT&T 6300, one for the Amstrad PC1512, and one for the IBM 3270 PC.
    The latter two are new drivers; these systems were not previously 
    supported by FreeGEM or GEM/3, only by GEM/2.

  * Pack 4 contains drivers I can't test because I don't have the hardware
    to hand. If anyone's got a working system with a Wyse, Genius, 
    AT&T Display Enhancement Board or Quadram Prosync, then feel free to 
    test them.
 
- I've also been on a little journey back in time (which is where I got the 
 PC1512 and 3270 PC drivers). At the bottom of the page is reconstructed 
 8086 source for the drivers supplied with GEM/3.1, GEM/2.2, GEM/2.1 and 
 GEM/2.0. 
   Many times on this journey, my thoughts have often been along the lines of
 "What *were* they thinking?" For example, the GEM/2.1 drivers only have
 half the font - but the complete font is there in both 2.0 and 2.2. The 
 GEM 2.2 8x16 font has much bigger button glyphs (see
 <http://www.seasip.info/Gem/History/gem2.html#sdpsc7> which aren't present
 in any earlier or later version.
   And another thing: GEM 2.1 added some functions so you could calibrate
 your Summagraphics tablet. These functions are also present in GEM 2.2, but
 in GEM 3.0 and later they disappear. Most of the code's still present in
 the driver, but you can't call it.

-- 
John Elliott