Re: Estimating bus load

[<kr...@bi...>]

Damien Douxchamps wrote:
> Hi all,
> 
> I'd like to estimate the load of a set of 1394 cameras on the bus in
> order to warn users when saturation is near. Does someone know how to do
> this? Or maybe briefly tell me what are the constrains governing the bus
> load? I'm a bit confused about how to relate packets, cycles, devices,
> bandwidth,...

You could just read out the contents of the BANDWIDTH_AVAILABLE 
register.  It is offset 0xfffff0000220 at the IRM node.  The contents of 
this register gives the amount of remaining bandwidth on the bus, 
measured in bandwith units.  A bandwidth unit is the time it takes to 
send a quadlet at S1600 - for example, sending 11 quadlets at S400 
requires 11 * 4 bandwidth units.  Of course, this only works if the 
applications that initiate isochronous streams allocate bandwidth as 
required.

Initially 4915 bandwith units are available: 1600 Mbit/s gives 6144 
quadlets/cycle (1600 Mbit/s * 125 us/cycle = 6144 quadlets/cycle), but 
only 80% of those can be reserved for isochronous traffic, 80% of 6144 = 
4915.

Kristian