RE: [oc] Anyone using VHDL procedures with Xilinx Webpack?

["Paul McFeeters" <paul.mcfeeters@ntlworld.com>]

Jim,

here is my biggest and most complicated function to date. Most people will
probably recognise it as a simple function to let me write a byte to an IDE
device's register via the PIO scheme. As the other function contains only
pin assignments and no conditional logic this is the likely cause of
Webpacks failure to process the VHDL properly.

impure function PIO_register_write ( p_DA : std_logic_vector (2 downto 0);
p_cs : integer ;   p_data : std_logic_vector (7 downto 0)  ) RETURN bit is
begin
	DA 		<= p_DA ;
	if (p_cs = 1) then
		-- register is in block 1
		cs1n 		<= '0' ;
		cs3n 		<= '1' ;
	else
		-- register must be in block 3
		cs1n 		<= '1' ;
		cs3n 		<= '0' ;
	end if;
	iocs16n  <= '1' ;	-- only 8 bit register transfers
	hi_byte  <= (others => '0') ;
	lo_byte 	<=	p_data ;
	return '1' ;
end function PIO_register_write ;

If you tell me where in this function the error maybe then I will be so much
the wiser. I'm not using macros or any string substitution system. When
having them as procedures failed miserably I converted them to functions
(then impure functions) and just return a '1' every time to validate them as
functions versus procedures. Even as functions they fail to compile due to
"exceptional errors" reported by Webpack.

I'm going to give up on coding VHDL by hand and just develop my Buffy-C
(working title for my version of Handel-C) then I can write a bloody IDE
interface in 30 minutes not 30 days (plus the C one will work). I've
probably spent %5 of my VHDL time putting new lines into the VHDL file and
the other 95% getting Webpack to allow it to compile. I realise I am a
newbie at VHDL but as I think up all my new projects in C terms so I want to
code it in C as well. Trying to convert mentally from C to VHDL is too much
for my set-in-its-ways brain to handle.

Paul

PS The code generated by Buffy-C doesn't contain any functions/procedures
and it never will until VHDL compilers can happily compile them.




-----Original Message-----
From: owner-cores@opencores.org [mailto:owner-cores@opencores.org]On
Behalf Of Jim Dempsey
Sent: 07 December 2001 16:52
To: cores@opencores.org
Subject: Re: [oc] Any using VHDL procedures with Xilinx Webpack?



----- Original Message -----
From: "Paul McFeeters" <paul.mcfeeters@ntlworld.com>
To: <cores@opencores.org>
Sent: Thursday, December 06, 2001 4:52 PM
Subject: RE: [oc] Any using VHDL procedures with Xilinx Webpack?


> Jim,
>
> if it is a recursion then I can't see it. Each procedure is literally just
> around 5 lines each "pin <= value" format, no special procedure/function
> calls at all. One procedure does have a "if param = value then -- else --
> end if" statement and uses an alias to reference the low byte in a word
but
> nothing more than that, definitely nothing I would even suspect as 'a
little
> dodgy'. All of these statements in their current form were used fine in
the
> expanded code so still clueless as to why Webpack should bomb.

Some times the littlest code segments produce the "can't see the forest for
the trees" effect.

Memory overflows on small code segments are commonly caused by
recursion. An example of this in C/C++ is where a #define macro
somehow rereferences itself or one of it's subordinates.

I am not up on this form of programming (VHDL) however if for example
you have a proceedure (macro?) called "ZooBie" and if the declaration
of macro "ZooBie" contains

    "if param = ZooBie then -- else -- end if"

You can see how this would expand forever.
To help locate this if your VHDL "compiler" has conditional
statement you could enable and disable sections of your code.
*** Note, some compilers expand comments and conditioned
out code. so you may also have to sprinkle in invalid characters
to prevent the recursion from occuring within a comment. e.g.

    #if(TRUE==FALSE)
    "if pa!!!ram = Zoo!!!Bie then -- else -- end if"
    #endif

Hope this leads you to a resolution

Oh, anicdotal information.

Several years ago I used Borland C++ (still do) and the version
of the compiler had a "bug" wherein if a particular token sequence
was split across compiler I/O buffer boundaries that an error would
be introduced into the code. Adding a well place extra space
character in a comment would usualy fix the problem.

Jim Dempsey


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