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

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:
> 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
> 

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?

>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?

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

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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'.

tnx for that.

Shreyas Kulkarni wrote:
> 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

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.