*** How the I2C protocol on the power board works: ***

Since the Linux driver for the Slug's bit-banged i2c adapter doesn't
support block read or write operations, it's necessary to do some
fudgery to sort out the transfers.  Unfortunately, read is now
different to write:

 * Block Write Operations
   These are pretty straightforward, and their format is the same as
   smbus block writes:
      Address R/W, Command, Length, Data x N, PEC
   This can be hacked up from userspace, including the checksum.

 * Read Commands
   These are more complex, because the number of bytes to be read are
   received during a read operation -- which isn't a supported feature
   from userspace.

   So, rather than implement the block transfer for the kernel, which
   would be a little experimental for this project, 

   It's necessary to set the command that we're doing:
   Address W, Command
   Address R, Length, *Command*, Data * N, PEC

   The important thing is that the read operation contains the command
   byte again -- which verifies that the write operation (which set
   the command) was successful.