Re: [pci] PCI target

[Duane Clark <dclark@leewardfpga.com>]

Miha Dolenc wrote:

> Hi all,
> it's been a while since we last talked here!
> 
> In fact, I did PCI master already and I'm resolving problems regarding
> timing for three weeks now. It's the problem that Duane is talking about - I
> want it generic and therefore problematic ;-( . I don't know anything about
> PCILOGIC yet - I will try and find it on the internet. Duane - do you know
> if this PCILOGIC block can be force used by specifying some constraints. If
> so - is this user, synthesys or physical constraint?
> Some syntax example would be nice also ;-) .
> 
> Thanx for your interest!
> 


It is a Xilinx primitive that you instantiate. Xilinx does not mention 
it in their library guide, but if you look at a Virtex or Spartan II 
chip with fpga_editor, look along the left and right sides, near the 
pins, about half way up. It is a very small block with six pins, so look 
carefully! There you will see a special block with dedicated wiring to a 
bunch of the IO blocks, and if you click on it, you will see that it is 
called PCILOGIC, along with the pin names.

I figured out what was in it by instantiating it into a small test 
design as a black box, then doing synthesis and place and route. Then I 
ran ngd2vhd, and the result was a VHDL model of the PCILOGIC. It turns 
out to be simple combinatorial logic. The key feature is the dedicated 
routing resources it has. The logic is something like this:

entity pcilogic is
	port(
		IRDY	:in  std_logic;
		TRDY	:in  std_logic;
		I1	:in  std_logic';
		I2	:in  std_logic;
		I3	:in  std_logic;
		PCI_CE	:out std_logic
		);
end entity pcilogic;

architecture primitive of pcilogic is
    signal nand_irdy: std_logic := '1';
    signal nand_trdy: std_logic := '1';
begin
    nand_irdy <= not IRDY nand not I1;
    nand_trdy <= not TRDY nand not I3;
    PCI_CE <= not ((not I2) and nand_irdy and nand_trdy);
end architecture primitive;

The I1, I2, and I3 pins are controlled depending on whether you are 

currently acting as a master or target.


Duane




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