Virtual device drivers are described in a section of "The Palm OS Companion" ,
The New Serial Manager -
Writing a Serial or Virtual Device Driver. This document is part of the Palm OS
3.5 SDK.
What I am trying to do is write a virtual device driver that will be able to
accept packets as they leave the
PPP network interface module, process them, then send them out the serial port.
Here are the results of my quest so far:
Virtual Device Drivers are new to the system circa Palm OS 3.3 or 3.5
They are a stand alone code resource, not an application.
There is no initialization code linked into the resource, i.e. no
StartupCode.lib
The File type of a virtual device driver is 'vdrv' not 'appl'
There is no source code for virtual device drivers currently available to the
public.
My current problem:
At boot up the New Serial Manager in the Palm OS searches the device for all
databases of type
'sdrv' and 'vdrv'. When it finds one it calls the 'DrvEntryPoint' function
which must be the first
function in the resource. ('main' if you will). This function fills in a
structure that is passed to it, with
information that the system needs to use the device driver.
When I load my device driver into the system and do a reset, the unit crashes
with the error message:
"General" 3.5 has just read directly from memory location zero (NULL). When I
attach the debugger
and step through the assembly code, I am in the middle of one of the Palm OS
system functions called
prvGetSerialDriverByCreator().
My real problem is trying to find individuals with information in this area. It
appears that no-one outside
of Palm (3com) has created one of these beasts.
-Ron Mercer
Certicom Inc.
Steve Sabram <[EMAIL PROTECTED]> on 30-03-2000 05:38:02 PM
Please respond to "Palm Developer Forum" <[EMAIL PROTECTED]>
To: "Palm Developer Forum" <[EMAIL PROTECTED]>
cc: (bcc: Ronald Mercer/Certicom)
Subject: Re: Virtual Drivers - Blood from a stone?
That is a pretty vauge statement. Since there is no established term for
"virtual device driver" in the PalmOS, can you elaborate
exactly what you intend?
Steve
Ronald Mercer wrote:
> Has anyone outside of 3com successfully build a virtual device driver? From
the
> questions and
> answers that I have seen so far these are rather dangerous waters I am
entering.
>
> "Here there be dragons" ;-)
>
> Any Comments?
>
> Ron Mercer
> Certicom Inc.
>
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