[DUG] Delphi Digest, Vol 139, Issue 15

[Jolyon Smith]

Based on this your declaration of the API function appears to be incorrect:

Documentation:

int API_PCDRead(HANDLE          commHandle,
                int:            DeviceAddress,
                unsigned char:  mode,
                unsigned char:  blk_add,
                unsigned char:  num_blk,
                unsigned char: *snr,
                unsigned char: *buffer);

Your declaration:

function API_PCDRead(comHandle: Thandle;
                     DeviceAddress: integer;
                     mode:          byte;
                     add_blk,num_blk:integer;
                     snr,buffer:pchar): integer;

Your *add_blk* and *num_blk* parameters are declared of type *Integer* (4
bytes) when the function is expecting parameters of type *unsigned char* (1
byte).  This explains your access violation (the result of the way that
memory used for passing parameters is handled when using 'C' calling
conventions, if the caller of a function, and the function itself, do not
agree on the exact sizes of the parameters being passed).

Change your function declaration to:

*function API_PCDRead(comHandle:       THandle;*
*                     DeviceAddress:   integer; *
*                     mode:            byte;*

*                     add_blk,num_blk: byte;
 snr,buffer:      pchar): integer;*

I would also double check the type declaration for the *Handle* parameter,
just to be certain that the "HANDLE" type expected by the API function does
in fact correspond to what appears to be the Windows API specific *THandle*
type that you have declared it as.

This will almost certainly solve your access violation.  Based on the
documentation it appears that the way that you are handling the result
following the call is correct (though I haven't examined it exhaustively).
You will do yourself an enormous favour by simplifying and tidying this up
as well as the initialization part.

Apart from anything else, it will greatly help someone maintaining the code
in the future if the variables used in the calling code correspond to the
parameters documented for the API.  e.g. if you are passing a buffer in a
parameter called "*snr*" then name your variable "*snr*", or *snrParam*,
and only access it that way.  Don't use a variable and a pointer that
happens to point to that variable (via a side-effect!) or if you absolutely
must then at least ensure that the names involved make this usage clear,
e.g. *snr* and *ptr**snr*.

Finally, the documentation also says that upon calling the function, the
*snr* buffer is expected to hold an *8 byte* key value which you are only
initialising with 7 bytes (6 x $FF and a $00) so I would double check that
this initialization of the *snr* buffer in your code is correct.


Hope this helps.


On 28 May 2015 at 18:27, Marshland Engineering <marshland at marshland.co.nz>
wrote:

> This is running with a USB cable and Windows XP. It installs as a HID
> device.
>
> 4.2    Mifare Appilication Commands
>
> 4.2.1 int
> API_PCDRead(HANDLEcommHandle,int:DeviceAddress,unsignedchar:mode,unsigned
> char:blk_add,unsigned char:num_blk,unsigned char:*snr, unsigned
> char:*buffer);
>
> Description:
> read the appointed length date at the appointed station
> Input Parameter Description
>
> commHandle      the serial port handle
> DeviceAddress   equipment address
> mode            read mode
>         ( Request Idle + Key A    mode=00 ,  Request Idle + Key B
>  mode= 02,
>         Request All  + Key A    mode=01 ,  Request All  + Key B     mode=03
>         the up number is hex）
> blk_add read block address
> num_blk read block amount
> *snr    a finger, transfer eight byte secret key
> *buffer wait receive the variable of output finger
>
> Output Parameter
> If Command success
>         *snr    4 byte card number
>         *buffer the read date (the fact number is num_blk*16)
> If Command Failure
>         buffer[0]       System Error/Status Codes(You can consult the 2.2)
>
> Return value:
>         0x00    Command OK. ( success)
>         0x01    Command FAILURE
>
>
> The full manual is here
> http://www.marshland.co.nz/ftp/Misc/DLL.doc
> Thanks Wallace.
>
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