You have to go round the houses a bit to get the information, but it's not too difficult.
First logon to the router and then select this address:
http://192.168.0.1/setup.cgi?todo=debugwhich should result in a screen which just says 'Debug enable'.
(That's assuming that you haven't changed the router's IP address from the default).
Then exit from the web interface and open a command-line window. Type:
telnet 192.168.0.1
You should get a BusyBox welcome message to confirm that your telnet connection is established.
Now type:
cat /proc/avalanche/avsar_modem_stats
This will give you a stream of information about the ADSL connection. Scroll up and find a section something like this:
[Upstream (TX) Interleave path]
CRC: 0 FEC: 0 NCD: 1
LCD: 0 HEC: 0
[Downstream (RX) Interleave path]
CRC: 0 FEC: 0 NCD: 0
LCD: 0 HEC: 0
[Upstream (TX) Fast path]
CRC: 1 FEC: 68 NCD: 0
LCD: 0 HEC: 0
[Downstream (RX) Fast path]
CRC: 49 FEC: 0 NCD: 0
LCD: 0 HEC: 0
In this example the interleave figures are all zero, apart from the first NCD value, which always seems to be 1, so this router is in fast mode. If you see zeros in the fast path sections and other figures in the interleave sections, then interleave is on.
Eric