smb(4): address format

M. Warner Losh imp at
Thu Jan 15 10:09:00 PST 2009

In message: <FC7CC7A3-18D5-4408-8F52-62B9DF189A74 at>
            Stefan Bethke <stb at> writes:
: Am 13.01.2009 um 13:43 schrieb Andriy Gapon:
: > So, in practice, there two conventions of specifying a slave address:
: > either as 0XXXXXXXb or XXXXXXX0b.
: Device datasheets generally specify the hard-wired or configurable  
: address as a bit string, with a slight preference to format that as  
: bbbb bbb.
: > In wider world 0XXXXXXXb format seems to be preferred, Linux also  
: > sticks
: > to it.
: I personally find having the address right-aligned a sensible choice.   
: I think of the address as logical unit, and normally would rather have  
: the SMBus bit banging abstracted away by the driver/hardware.

The format that is preferred on FreeBSD is xxxxxxxx0b.  That's the
format that the existing IIC bridge drivers use and deal with.  I've
not looked at the SMB drivers, but I went through all the iic bridge
drivers in the 6.x time frame and made sure they were all consistent.
If I missed the smb drivers, that's my bad.

I could find no evidence that there was a format that was more
preferred apart from the dozen data sheets that I'd read at the time
which used the xxxxxxx0b.


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