Re: [FFADO-devel] Am I just really bad at math or is something wrong here.

[Daniel W. <wa...@mo...>]

> When I look at what I am asking for, I see this
> 
> 48000 samples/second  32 bits/sample  8 channels  4 units
> 
> One unit gives me 12,288,000 bits/second
> Four units give me 49,152,000 bits/second which is sooooo far south of 400Mbits/second that I
> don't think protocol overhead is going to be a major factor here.

The default configuration of a firepod is something like this:

8 Line In
2 S/PDIF In
1 Mini In

8 Line Out
2 S/PDIF Out
1 Mini Out

makes together 2*11 channels. Each channel is 1 quadlet (32 bits) on the 
bus.

With the protocol overhead (8 events are group into on packet):
1 ISO header  (1 quadlet)
1 CRC header  (1 quadlet)
2 CIP headers (2 quadlets)
8 Samples     (8 quadlets)
1 CRC payload (1 quadlet)

Size of one packet is 13 quadlets (52 bytes).

2 streams (PC->device, device->PC):
2 * 6000 packets per second = 12000 packets per second

One device gives me: 12000 * 52 bytes = 624000 bytes/s = 4992000 bits/s
Four devices gives me: 19968000 bits/s

So it still should fit on one bus, though about 50% of the bandwidth is 
used.

> Am I just stupid or is there a bug in libiec61883 or freebob?

 From the error message it looks like libiec61883 reports it is unable 
to allocate the bandwidth. Could you try with one device first and then 
add the second then the third?

daniel