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From: Antti on 12 Oct 2006 05:46
Hi,

Virtex-4 has many new things, one of them is access to CCLK as output
after configuration. CCLK control is required to readback data from XCF
devices, this approuch is described in Xilinx Application note XAPP482.
Until today I did live in believe that this was the reason why startup
primitive was modified in Virtex-4, but today I was about to check the
pinout for XCF data read able design, and uuuuups - CCLK access is
added in Virtex-4 but at the same time input access to DIN has been
removed!? Or at least I cant see how to read the DIN pin from FPGA
fabric. So if for Spartan-3 the XAPP482 solution suggested a FPGA I/O
pin to be routed parallel to CCLK, then well this wire is not required
in Virtex-4, but now we need another FPGA I/O to be routed to DIN
because DIN is no longer accessible?

I cant belive this to be true ! But I also fail to see any other
solution for XCF data read with Virtex-4. Of course a solution would be
using Virtex-5 where the DIN is again made accessible with the modified
again STARTUP primitive.

I am too glad that I did not trust me belives that the CCLK fix in the
Virtex-4 fixed the additional wiring requirement as per XAPP482 and
checked the design before submitting to PCB fabrication.

I wish Xilinx would update XAPP482 with wiring diagram for all
families. The DIN no access thing was really an almost unbelivable
surprise for me :(

Antti

From: "Sylvain Munaut SomeOne@SomeDomain.com>" on 12 Oct 2006 06:43
Hi

> Virtex-4 has many new things, one of them is access to CCLK as output
> after configuration. CCLK control is required to readback data from XCF
> devices, this approuch is described in Xilinx Application note XAPP482.
> Until today I did live in believe that this was the reason why startup
> primitive was modified in Virtex-4, but today I was about to check the
> pinout for XCF data read able design, and uuuuups - CCLK access is
> added in Virtex-4 but at the same time input access to DIN has been
> removed!? Or at least I cant see how to read the DIN pin from FPGA
> fabric. So if for Spartan-3 the XAPP482 solution suggested a FPGA I/O
> pin to be routed parallel to CCLK, then well this wire is not required
> in Virtex-4, but now we need another FPGA I/O to be routed to DIN
> because DIN is no longer accessible?
>
> I cant belive this to be true ! But I also fail to see any other
> solution for XCF data read with Virtex-4. Of course a solution would be
> using Virtex-5 where the DIN is again made accessible with the modified
> again STARTUP primitive.
>
> I am too glad that I did not trust me belives that the CCLK fix in the
> Virtex-4 fixed the additional wiring requirement as per XAPP482 and
> checked the design before submitting to PCB fabrication.
>
> I wish Xilinx would update XAPP482 with wiring diagram for all
> families. The DIN no access thing was really an almost unbelivable
> surprise for me :(

Isn't this what the USE_ACCESS_VIRTEX4 is for ?

Sylvain

From: "Sylvain Munaut SomeOne@SomeDomain.com>" on 12 Oct 2006 06:45

> Isn't this what the USE_ACCESS_VIRTEX4 is for ?

sorry, it's
USR_ACCESS_VIRTEX4
(typo)

From: Antti on 12 Oct 2006 06:56
Sylvain Munaut <SomeOne(a)SomeDomain.com> schrieb:

> > Isn't this what the USE_ACCESS_VIRTEX4 is for ?
>
> sorry, it's
> USR_ACCESS_VIRTEX4
> (typo)

No.
USR_ACCESS is nice thing but has nothing todo with missing access to
DIN pin on V-4

Antti

From: Antti on 12 Oct 2006 07:05
Antti schrieb:

> Sylvain Munaut <SomeOne(a)SomeDomain.com> schrieb:
>
> > > Isn't this what the USE_ACCESS_VIRTEX4 is for ?
> >
> > sorry, it's
> > USR_ACCESS_VIRTEX4
> > (typo)
>
> No.
> USR_ACCESS is nice thing but has nothing todo with missing access to
> DIN pin on V-4
>
> Antti

Hm after thininking - well USR_ACCESS doesnt allow direct access to the
DIN, but if the configuration memory has appended a specially formatted
bitstream block with USR ACCESS commands in it, then seeking the memory
to correct position and toggling the CCLK with the help of STARTUP_V4
then the data from configuration memory will appear on USR_ACCESS
outputs (And that data comes from DIN). But this indirect way is not
useable in the current design.

Antti

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