How to achieve a long burst?

[Henry Gong <henry.gong@radiata.com>]

Dear all,


There is a popular view that if you want a long burst, you have to be a
bus master.  It sounds reasonable but nobody can tell me why. Can
anybody explain please?

If the PC has a large block of data to send to the PCI card, here is
what an experienced PCI engineer likes to do:
    1. The host sends a message to the PCI card informing the starting
address;
    2. The PCI card starts a "Mater Read".

In this way, the transfeer is done in two steps. This is certainly not
efficient for short bursts. It is supposed to be good for long burst.
But why cannot the host simply start a master write. Then the PCI card
responds in "Slave Read"? People beleive that the host does not like to
use long
bursts. It normaly separates a long burst into many short bursts. Is
this true? Why?

If the host sends a block of data to a PCI card, how long burst in data
can it
normally achieve, 20, 200 or 2000?

If a PCI card sends a block of data to the host, how long burst in data
can it
normally achieve, 20, 200 or 2000?

How can device driver control the burst? For example, why do people say
3D graphic normally uses many short bursts?

Sorry to ask so many questions. Any explanation and comment, even blame,
is appreciated.
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