Re: 64-bit on-board devices on 32-bit PCI bus

[ANAND KURIAKOSE <Anand.Kuriakose@smartm.com> (by way of Daniel Weaver <dan.weaver@znyx.com>)]

	Hi venkatesh,

	>>U should not provide any on-board pull-ups, incase if u use same
extension board for 64-bit connector, there are pull-ups for all the data
lines on mother-board also, due to two pull-ups on each data line, there
will be more pull-up current. So upper 32-bits must be unconnected.

	When i meant on-board pull-ups, i meeant on the motherboard and not
on the add-on card.

	>>Configure Ur device in output mode(upper 32-bits), when u insert
it in 32-bit slots(according to REQ64# logic), drive zero/one onto the upper
32-bit bus.

	I looked up the register set of the devices,could not locate any
register where i can do the seting mentioned above. 

	Thanks,
	Anand.



	From:	Venkateshwarlu V <venkateshwarluv@myw.ltindia.com> on
07/31/2002 11:14 AM
	To:	ANAND KURIAKOSE/Apex Data Inc/01@Apex Data Inc,
pci-sig@znyx.com@SMTP@Exchange
	cc:	Gopal Savanur <GopalS@myw.ltindia.com>@SMTP@Exchange 

	Subject:	Re: 64-bit on-board devices on 32-bit PCI bus

	** Proprietary **

	Hello Mr.Anand,
	I will try to answer ur questions here.

	Should i provide on-board pull-ups on the upper 32-bit extension or
just leave
	them unconnected?
	U should not provide any on-board pull-ups, incase if u use same
extension board for 64-bit connector, there are pull-ups for all the data
lines on mother-board also, due to two pull-ups on each data line, there
will be more pull-up current. So upper 32-bits must be unconnected.
	 I personnaly feel that the 32-bit extension of these individaul
devices should
	be left unconnected (hoping that the devices will take care of
preventing the
	bus from floating).
	The device cannot take care of preventing from floating
	 The other thing i thought if i provided a common on-board
	pull-up for the 32-bit extension of both these devices is that there
could be
	probable data contention, because at any time and on any of the
upper 32-bit
	signals, the two devices could be driving opposite levels. Am i
right in
	thinking in this direction?
	Sol'n: Configure Ur device in output mode(upper 32-bits), when u
insert it in 32-bit slots(according to REQ64# logic), drive zero/one onto
the upper 32-bit bus.



	>>> <Anand.Kuriakose@smartm.com> 07/30/02 11:00PM >>>


	Hi,

	As per the PCI spec 2.2, sec 3.8.1, the 32-bit PCI extension has to
be pulled on
	the  motherboard, to prevent them from floating. Heres a situation
where the
	motherboard has a 32bit PCI bus . There are two on-board 64-bit PCI
devices (LAN
	and SCSI) on the 32-bit bus. Again, as per the PCI spec 2.2, sec
3.8., we see
	that these PCI devices monitors the REQ64# signals during PCI reset
de-assertion
	to determine the width of the PCI bus. In the above case, these
devices will see
	that the REQ64# signals is de-asserted during reset de-assertion and
hence
	conclude that the bus width is only 32-bit. Upon determining that
the bus width
	is 32-bit, these devices will start driving valid bit patterns on
the upper
	32-bit extension in order to prevent the bus from floating. So heres
the
	question.

	Should i provide on-board pull-ups on the upper 32-bit extension or
just leave
	them unconnected?
	 I personnaly feel that the 32-bit extension of these individaul
devices should
	be left unconnected (hoping that the devices will take care of
preventing the
	bus from floating). The other thing i thought if i provided a common
on-board
	pull-up for the 32-bit extension of both these devices is that there
could be
	probable data contention, because at any time and on any of the
upper 32-bit
	signals, the two devices could be driving opposite levels. Am i
right in
	thinking in this direction?

	Thanks in advance.

	Anand.