GNOKII Hackers Guide
--------------------


Purpose
-------

Now that we know in some detail the workings of the protocols it makes
sense to organise the gnokii code to fit them better.  This should mean
that when new models come out, it is easier to get the code in place to
support them.  It is hoped that the new structure will also work for other
makes of phone.


Overview:

Application (gnokii/xgnoki)
    |  do_something()
(Middle-layer aka gnokii API)
    |  gsm->function() 
gsm-api
    |  p*_functions()
Phone specific code (eg nk7110.c)
    |  gn_sm_message_send(), gn_sm_wait(), gn_sm_loop()
StateMachine
    |  sm_send_message(), sm_loop()
Link specific code  (eg fbus.c)
    |
Hardware code



Detailed operation
------------------


Initialisation:

The gnokii application (eg gnokii, xgnokii) decides on the phone type and
required connection method from the config file.  It then calls the
gsm-api init code which in turn calls the init code for the correct phone.  
This code is located in a series of files phone/*.c.  This code creates a
gn_state structure (which contains a gn_link structure) and passes this
to the common code for the specific link (eg fbus_initialise, contained in
fbus.c).  The link code fills in the gn_link part of state (and
also stores state to use later).  The phone code chooses the appropriate
link and is free to perform any phone specific init.  It then initialises
the StateMachine by passing it the state struct and a gn_driver struct.


The Link:

The link serves to deal with bits of the phone protocol which are common to
every exchange for that particular phone.

The gn_link structure is used to contain any information about the link
which is required by the StateMachine.  Two vital functions in the link
are sm_send_message and sm_loop:

sm_send_message(u16 messagesize, u8 messagetype, void *message)
   is the function called by the statemachine code to send a message 'down
   the pipe'.  The parameters are intended to be generic (though with 
   obvious origins :-)  For example 'at' commands could be enumerated and 
   passed as messagetype.

sm_loop(struct timeval *timeout)
   is a function which must be called regularly by the statemachine code
   to enable to link code to process date from the phone.  This is due to 
   the code now being single threaded and using select/poll.  The timeout 
   passed can therefore be used to make this function block for a while 
  (or not).

In the loop function, the link code checks for any incoming messages from
the phone.  Any received correctly are passed up to the statemachine code.


The Middle Layer

All common/*.c files contain the code that is general and is used by all
of the phones. The functions within should convert the gnokii internal
structures into the frames (without the header) that can be sent to the
phone and understood by it. It's obvious that this layer should be phone
independent. All the phone specific stuff should be done in the phone layer.
In the case when phone frames are similiar but not the same, the phone layer
can export some help structures to let be the code shared in the middle
layer. Using the middle layer is optional. Currently almost no code does use
it. Although it is recommended to use it to avoid the code duplication and
to keep clean the phone drivers.


The Phone:

The phone/*.c code therefore basically contains code to package up and
unpack information from the phone specific format to generic gnokii
structures (eg gn_bmp).  However, it is also at the top of the tree
and contains functions called by the application.  Generally there are
three types of exchanges that can occur.  Firstly the computer can send
the phone a command and expect no answer (not including acks etc which 
are dealt with by the phone code).  Secondly the computer may send a command
and expect a response within a certain time - often containing useful 
information.  Lastly the phone may send the computer unrequested 
information (ring!).  Therefore the functions in the phone code need to 
process one of these three things:

1) Just sending out is easy - we simply call gn_sm_send_message - which in
turn calls the link sendmessage.

2) Command and response.  There are two ways to do this.  In both cases we
start out by sending a message via the statemachine.  Next we either a)
wait for the reply or b) wait for some other code to process the reply.  
My (*new improved*!!!) suggestion is that the statemachine calls phone
functions (like parts of DispatchMessage) which process the received data
into a generic structure tagged with the data type (one function for each
data type).  This is returned to the statemachine.  The statemachine then
returns this 'baggage' to the other part of the phone code which is
waiting for it.

3) Notification.  Here, as for 2) the statemachine calls some phone code,
but the phone code merely remembers it and does not return any data.


So, the phone file contains two types of functions.  Some are called by
the application (via gn_functions) - and some by the statemachine
(IncomingFunctions[]).  The application ones assemble a request and pass
it on down to the statemachine.  They then block to the statemachine until
the answer is ready.  The statemachine recieves data from the link and
passes it up to the appropriate IncomingFunction in phone, which returns
the answer which is finally passed back to the blocked phone function.


The StateMachine: 

This therefore has the following states:

Startup
Initialised
MessageSent
Waiting
AnswerReady

When gn_sm_send_message is called by the phone (application code), we go to
state MessageSent.  The message is passed on to the link, but stored
internally as well in-case it needs to be resent.

If at any point an message from the link is received this is passed onto
the phone (incoming) code.

If the phone code calls gn_sm_waitfor, we go to state Waiting.  Now if an
answer comes back from the phone code (eg a received logo) we store it
internally in the statemachine and go to state AnswerReady.

When the phone code calls sm_get_answer, we pass up the stored answer and
go back to Initialised.

Note that all of this can, or can not be done as a seperate thread.  For
now, we will have a gn_sm_loop function (which blocks for a required time and
returns the current state) so that we can work within one thread.


PhoneGeneric:

This now contains one handy helper function which serves only to call
gn_sm_waitfor, then gn_sm_loop repeatedly until the state goes to AnswerReady,
and then sm_get_answer.  This is just to save repeating code.


-----------------------

Note that this leaves the phone code very similar to the basic layout of
eg fbus-6110.c but removes all the:

static gn_timestamp	*CurrentAlarm;
static gn_error		CurrentAlarmError;

makes everything well orderd and splits up DispatchMessage into byte
sized chunks!

-----------------------



Other Notes
-----------

Within a phone/*.c or link file the functions should be made static.  It
is therefore not necessary to use prefixes such as FB61_ but this may help
code legibility to distiguish the major functions.


-- 
$Id: gnokii-hackers-howto,v 1.4 2002/12/08 23:10:31 pkot Exp $
Chris Kemp
Pawel Kot
