pinvoke ceddk.dll

[Leela]

I am new to wince and am having various issues trying to do some basic
io routines. From reading the other posts, I have gained a wealth of
information regarding utilizing ceddk for doing this. I am trying to
utilize pinvoke to call READ_PORT_UCHAR() and WRITE_PORT_UCHAR() w/in
CF written in VB. I am using an x86 based platform and I have verified
ceddk.dll in the \windows on the CE device.

So far I have:

<DllImport("ceddk.dll")> _
Public Shared Function READ_PORT_UCHAR( _
ByRef Port As int16 _
) As Byte
End Function

<DllImport("ceddk.dll")> _
Public Shared Function READ_PORT_UCHAR( _
ByRef Port As int16 _
) As Byte
End Function

the io base port address is 0X300 and I am trying to read the lower
nibble at 0X303

and when I pass in an int of 771 ( 0X303) I get a return of 255 from
READ_PORT_UCHAR() when the actual read should be 0X000 or 0
I've verified that the return read should be 0 by booting into dos and
using the inportb function.

As a matter of fact, no matter what I pass in (any int value), I get a
return read value of 255.

Please help.... any help is greatly appreciated. Thanks in advance.

 

[Guest]

A UCHAR is 16 bits, a byte is only 8, so that's going to cause you major
grief with your definitions right there.

 

[Leela]

Well, among other things I've tried port as byte datatype..... but how
do you pass in an address of 0X303 (int of 771) as a byte value? or
am I completely off base here.

 

[Guest]

You can't. You'd need READ_PORT_USHORT, which is a UInt16 (short). I'm no
x86 expert, but addresses are using 32 bits, so you'd probably want to be
passing a full DWORD anyway, not a byte or a short, so maybe READ_PORT_ULONG
is most appropriate for your goal.

 

[Leela]

I've also tried the following function call with integer datatype...

<DllImport("ceddk.dll")> _
Public Shared Function READ_PORT_ULONG( _
ByRef Port As Integer _
) As Integer
End Function

and I returned a value of -1 when passing in an address of 771
(0X303) .... when I was expecting a value of 0X000. Once again no
matter what address I pass in, I am returning a value of -1

 

[Guest]

Should be ByVal, not ByRef - you want the address itself, not a pointer to
it.

-Chris

 

[Leela]

that did the trick...... thank you very much for all the help, I was on
the brink of going mad and you saved me. Kudos to google groups and
Chris.