How to handle incompatible modems?

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nelson@crynwr.com (Russell Nelson) wrote:
> I want to add support to mgetty+sendfax for modems based on the Cirrus
> MD9624 chipset.  It's possible to automatically identify what modem is
> being used via the ATIn command.  So I would say that the different
> commands/code should be hidden behind variables and pointers to
> functions (as opposed to ifdefs).  Any suggestions on how I should do
> this?

This is something which I will have to do myself to support the
Rockwell voice commands in vgetty. I was thinking about two
separate steps:

- modularize the routines further, I would like to have no 
  explicit modem commands in routines like voice_send_file
  if possible.

- create a structure which contains modem-specific settings.
  This could contain a variety of stuff, i.e. booleans
  to indicate if a feature is available, numeric codes
  (i.e. maximum speaker volume), init strings, etc.

  I'm thinking about putting in function pointers too, this
  way you could replace one of the bottom-level functions
  entirely without having to add tons of conditionals.
  I.e., create a rockwell_do_beep() and zyxel_do_beep()
  and initialize the structures appropiately. This might
  be more readable than having to search through the 
  structure initializations to find out what exactly is
  being sent to the modem.

It would be elegant if a new function, identify_modem(),
could reliably detect the modem type and initialize the
structure appropiately. That way, you wouldn't even
need to mess around with config files for this.

Klaus
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