On Sun, Jul 13, 2008 at 5:13 PM, Jean Delvare <[EMAIL PROTECTED]> wrote: > On Sun, 13 Jul 2008 16:53:19 +0800, eric miao wrote: >> >> 3. for chips like max732x, actually, the range of 0x50 - 0x5F will be >> >> monitored by the I2C chips at startup to decide the connections of >> >> AD2/AD0 pins to GND/VCC/SCL/SDA, so actually, even if the chip >> >> is finally decided at, say 0x56, no sane hardware designers will put >> >> another chip whose address falls between 0x50-0x5F together with >> >> such a max732x chip, ugly, but true. >> > >> > Why do these chips have a selectable address at all then, if they >> > virtually use all the range of possible addresses? I don't buy this >> > point at all. I see no reason why putting another chip in the same >> > range would cause any problem. >> >> Selectable address is used to decide the initial state of each >> pin (especially the output level). Due to the fact that SCL/SDA >> are initially held high, the chip has to monitor the first I2C activity >> to decide if AD2/AD0 is tied to one of GND/VCC/SCL/SDA. > > Ah, OK. I had missed the fact that the address had an impact on the > initial pin states. This sounds a bit weird to me, BTW, as the chip > doesn't know its address before the first transaction on the I2C bus, > it also can't set the pins to their "initial" state before the first > transaction on the I2C bus. This is a strange definition of "initial > state" if you ask me. > > Anyway, this still doesn't prevent other I2C chips from using other > addresses in the 0x50-0x6f range on the same bus.
OK, I see. > >> So , do you see any chance of this getting merged during this >> window? If that's possible, please consider merge, thanks. > > You probably want to read MAINTAINERS again, to find out that I am not > the maintainer of the gpio subsystem. Ask David Brownell, or Andrew > Morton. Well, I don't mind your optional Acked-by to the I2C part :-) And David, apart from my misunderstanding of the I2C address, which I don't think have impact to the patch itself, can I have you Acked-by so I'll mail Andrew Morton to see his willingness to include this into -mm tree? (Or you have a plan to have a dedicated gpiolib tree, which I don't mind either) > > -- > Jean Delvare > -- Cheers - eric _______________________________________________ i2c mailing list [email protected] http://lists.lm-sensors.org/mailman/listinfo/i2c
