[pvrusb2] how to change channels using sysfs

[Robert Casper]

Hello,

My question is about using Sysfs to select an analog cable TV channel.  

I understand how to write a value to a cur_val file, and have switched
between television and composite inputs with no problem.

Writing a number to the ctl_channel control doesn't work for me.  If I
echo a 3 to select channel three, there's no error message but the value
remains at 0.

I see there is ctl_frequency and a frequency table, but I am selecting a
cable TV channel, not tuning to a broadcast frequency.  Would I have to
find a frequency number that corresponds to each cable channel?  If so
how would I do that?

Thanks
Robert