PCI doubt

hi there,

i have a (probably very fundamental) doubt regarding PCI - what is the difference between a PCI master, arbiter and initiator? they all look same to me.

TIA, Shreyas

Reply to
Shreyas Kulkarni
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That is a very good question, because at least my PCI standard Rev 2.1 has none of these in the index, and only lists master in the Glossary. master = an agent that initiates a bus transaction agent = an entity that operates on a computer bus Entity and bus are not defined, but an entity is apparently a bus device bus device = A bus device can be either a master or a target I love standards ;-)

Seriously, Master and Initiator are the same. An arbiter is something completely different. It exists once per bus and resolves confliicts if multiple masters request acces to the bus. See the REQ# and GNT# signals of each master are connected to the arbiter.

Kolja Sulimma

Shreyas Kulkarni wrote:

Reply to
Kolja Sulimma

does it mean that a target only PCI device can be master as well as slave? master when initiating data trasnfer and slave when on the receiving end?

Reply to
Shreyas Kulkarni

target == slave the end that responds to a read/write from someplace else initiator == master

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Reply to
Hal Murray

In PCI, masters are called initiators and slaves are called targets. A target only device can never initiate a transfer on the bus. It may be read or written by other initiators.

A PCI device can be both a master and a slave but it wouldn't be called 'target only'.

Reply to
pdstroud

tnx for that.

Reply to
Shreyas Kulkarni

The arbiter is a seprate function that decides which initiator gets the bus. Initiators request the bus and the arbiter grants the bus to one initiator at a time. Every PCI bus must have one and only one arbiter.

Reply to
RobJ

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