[PATCH] i2c: rk3x: adjust the LOW divison based on characteristics of SCL
addy.ke at rock-chips.com
Thu Sep 25 19:40:41 PDT 2014
On 2014/9/26 10:08, Doug Anderson wrote:
> On Thu, Sep 25, 2014 at 6:40 PM, addy ke <addy.ke at rock-chips.com> wrote:
>> Hi, Doug
>> On 2014/9/26 5:52, Doug Anderson wrote:
>>> On Wed, Sep 24, 2014 at 9:36 PM, Doug Anderson <dianders at chromium.org> wrote:
>>>> On Wed, Sep 24, 2014 at 6:56 PM, addy ke <addy.ke at rock-chips.com> wrote:
>>>>> In my measurement,all paramter but "Data hold time" are match the characteristics of SCL bus line.
>>>>> the measured value is 0.928us("data hold time on RK3X" ~= "the low period / 2")
>>>>> but the maximum value described in table is 0.9us
>>>>> About "Data hold time", there are described in I2C specification:
>>>>> - for CBUS compatible masters for I2C-bus deivices
>>>>> - the maximum data hold time has only be met if the device does not stretch the LOW period of the SCL signal.
>>>>> I have tested on RK3288-Pinky board, there are no error.
>>>>> But I don't known whether this paramter will affect i2c communications.
>>>> I'll have to spend more time tomorrow to really understand this, but
>>>> if changing the code to bias towards slightly longer "high" times
>>>> instead of "low" times helps fix it then that's fine with me.
>>> So what you're saying is that you're seeing a case where the clock
>>> goes low and the data is not valid until .928us. Is this data that is
>>> being driven by the master or data that is being driven by the slave?
>> It is driven by the master and will be release at half of LOW period in our IC design.
> Ah, I didn't know this. Is that in the TRM somewhere?
No, it was my test and confirmed by IC engineer.
You can find that there is a pulse at half of LOW period of the ninth SCL clock each bytes.
> ...so does it work to just replace:
> ideal_low_div = DIV_ROUND_UP(clk_rate * min_low_ns,
> scl_rate * 8 * min_total_ns)
> ideal_low_div = min_low_div
> That will assign all "extra" time to the "high" part.
I Think it is more reasonable.
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