Re: devices not seen, fpgas not getting the clock

[Stefan Spaeth <S.Spaeth@alcatel.de>]

"Marco Brambilla (Wireline)" wrote:
> 
> Hi all,
> 
> As someone else on the list, I too had some issues with clock not seen
> by fpgas.
> 
> In our case we have many HP PCs which are working fine.
> In only one PC (a P3 500) we saw that during the initial boot phase the
> clock is present on all 3 PCI slots on the motherboard.
> 
> After some seconds (5 to 30) the clock remains good on populated slots,
> while it is removed from empty slots.
> At least this is what our lab people told me.
> 
> The PC is thus fully functional, but we have a development board on
> which our chip is implemented in fpga.
> For debugging reasons we cannot program the FPGA from the external
> memory, but from the jtag cable.
> This means that our board can never be seen by the motherboard, because
> at startup it was not operating, so the clock is removed from the slot.
> 
> Has anyone ever heard of such a behaviour ?

yes, this seems to be a common option now for Athlon - and likely
also PIII mainboards. I first read about it in an article in the
computer magazine c't (http://www.heise.de/ct).
It is a feature that is thought to reduce EMI.

> Is this "clock removing" feature really present ? (and can it be
> disabled) ?

You should be able to find an option in your motherboard's BIOS.
Look for: "Clock for Empty PCI Slot/DIMM" or "Clk-Ge for PCI Slot",
or "Stop Un-used PCI Clock"; these were the options listed in the
above mentioned article;
Obviously they also sometimes remove the clock from unused DIMM slots.

Stefan

> Thanks for any advice.
> 
> Marco Brambilla
> 
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> 
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