Hi,
On 18-03-15 09:20, Hans de Goede wrote:
Hi,
On 17-03-15 12:15, Hans de Goede wrote:
Hi,
On 17-03-15 11:08, Stefan Roese wrote:
The current implementation for baudrate calculation is incorrect. This part from the formula:
"2 ^ (n + 1)" is not equivalent to (1 << n) but to (2 << n)!
This patch fixes this and moves this calculation to a function instead of using a macro.
Hmm, this does not match with what the Allwinner datasheets say: https://github.com/allwinner-zh/documents/blob/master/A20/A20%20user%20manua...
They say:
Fsamp = F 0 = Fin / 2^CLK_N F1 = F0 / (CLK_M + 1) Foscl = F1 / 10 = Fin / (2^CLK_N * (CLK_M + 1)*10)
With Foscl being the ultimate i2c speed. Notice that they are talking about 2 ^ CLK_N not 2 ^ (CLK_N + 1)
And they have a few examples which match this. Now it could be that a register value of 0 means CLK_N = 1, reg 1 CLK_N = 2, etc. this is not clearly specified ...
This new function is taken from the Linux kernel.
Interesting, because on Allwinnner / sunxi devices we are using the kernel driver formula unmodified, and things seem to work fine despite this. Could be tolerances allowing this, could be the Allwinner datasheet being unclear.
I've send allwinner a mail asking them to clarify this.
I've just gotten an answer from allwinner, and the formula in their datasheet is correct, with the raw register value == CLK_N so the current (before this patch) u-boot code is correct for Allwinner devices and we need a #ifdef here to keep the old formula for sunxi devices, you can use:
p.s.
This means the kernel currently does the wrong thing on Allwinner, I've put fixing this on my todo list.
Regards,
Hans