Huang Changming-R66093 <[email protected]> wrote on 2011/10/27 11:26:04: > > > > > > The above sequence is different than the kernel version, why? > > > > > > > > I don't know the kernel version, but I write the u-boot code > > according > > > > to the Reference Manual of PowerPC, e.g p1022: > > > > 11.5.6 Generation of SCL When SDA Low > > > > It is sometimes necessary to force the I2C module to become the I2C > > bus > > > > master out of reset and drive SCL(even though SDA may already be > > driven, > > > > which indicates that the bus is busy). This can occur when a system > > > > reset does not cause all I2C devices to be reset. Thus, SDA can be > > > > driven low by another I2C device while this I2C module is coming > > out of > > > > reset and stays low indefinitely. The following procedure can be > > used > > > > to force this I2C module to generate SCL so that the device driving > > SDA > > > > can finish its transaction: > > > > 1. Disable the I2C module and set the master bit by setting I2CCR > > to > > > > 0x20 > > > > 2. Enable the I2C module by setting I2CCR to 0xA0 > > > > 3. Read the I2CDR > > > > 4. Return the I2C module to slave mode by setting I2CCR to 0x80 > > > > > > > Compare with kernel version, the difference is one line: > > > Uboot: readb(&dev->dr); > > > Kernel has no any operation. > > > But, I check the comment of kernel, because the 9th clock pulse isn't > > generated, > > > the sequence of function mpc_i2c_fixup is needed to generate 9th > > clock pulse. > > > > Not so, there is more than that if you look closer. The description in > > the kernel > > is a bit misleading(or so I think). I prefer the kernel version for 2 > > reasons: > > 1) It has been there for quite some time so if there were something > > wrong with, > > it should have been noticed by now. > > 2) I have a vauge memory of checking it again the mpc8321 manual and I > > was happy > > with it. > > > These tow part codes are doing the different thing due to the different > reason: > 1. Kernel's code: > because Sometimes 9th clock pulse isn't generated, that code is to generate > the 9th clock pulse.
What code are you looking at? Are you just reading the comment? Look at http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commit;h=0c2daaafcdec726e89cbccca61d576de8429c537 to get a clue. Your code isn't complete, you cannot trust the manual to be the whole truth. Jocke _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
