* Re: About RK3288 i2c scl duty cycle
[not found] ` <CAD=FV=VEUVxxZ8ZP89qhSOmvX_LgMvnczNx17qdMTGCapZj3uw@mail.gmail.com>
@ 2014-09-18 1:26 ` addy ke
2014-09-18 4:17 ` Doug Anderson
0 siblings, 1 reply; 2+ messages in thread
From: addy ke @ 2014-09-18 1:26 UTC (permalink / raw)
To: dianders
Cc: max.schwarz, heiko, wsa, huangtao, cf, linux-i2c, linux-kernel,
linux-kernel, linux-arm-kernel, linux-rockchip
Add public list
On 2014/9/17 23:17, Doug Anderson wrote:
> Addy,
>
> On Tue, Sep 16, 2014 at 6:30 PM, addy.ke@rock-chips.com
> <addy.ke@rock-chips.com> wrote:
>> hi, all
>
> Any reason why you didn't add some public lists? It seems like this
> is a perfect discussion for linux-i2c.
>
>
>> According to i2c-bus specification(version2.1, page 32, Table5, FAST-MODE):
>> The minimum LOW period of the scl clock is <1.3us>, and the minimum HIGH
>> period of the scl clock is <0.6us>.
>> T(min_low) : T(min_high) ~= 2 : 1
>>
>> If <DIVH = DIVL> in fast mode(scl rate = 400Khz)
>> 1)Under ideal conditions, T(scl_low) = T(scl_high) = <1.25us>
>> 2)Our measurement, T(scl_low) = <1.3us>, T(scl_high) = <1.25us>
>>
>> The low period of the scl clock is critical.
>>
>> Do we need set <DIVL:DIVH = 1 : 2> to increase T(scl_low)? // T(scl_low )
>> : T(scl_High) = 2 : 1
>
> I can't say I've ever looked at that pat of the i2c spec before, but
> what you say seems reasonable to me. ...well for 400kHz, at least.
> At 100kHz you shouldn't use the same 2:1 ratio.
Yes, in normal-mode(100K) we can be only used 1:1 ratio.
But in FAST-MODE maybe we must use 2:1 ratio.
----
In Table 5(Characteristics of the SDA and SCL bus lines for F/S-mode I2C-bus devices)
1)FAST-MODE(400K):
The minimum LOW period of the scl clock 1.3us
the minimum HIGH period of the scl clock 0.6us
T(min_low) : T(min_high) ~= 2 : 1
But I can't see any ratio about In FAST-mode(400k) and Normal-mode(100k).
2)Normal-MODE(100K):
The minimum LOW period of the scl clock 4.7us
the minimum HIGH period of the scl clock 4.0us
T(min_low) : T(min_high) ~= 1 : 1
3) HS-mode(3.4M)
ratio of 1 to 2 is required, decribed as follows:
Hs-mode master devices generate a serial clock signal with a HIGH to LOW ratio of 1 to 2
>
> I'm sure other drivers have solved this problem too, so maybe you can
> copy some code. In i2c-designware-core.c you can see them doing all
> the calculations you need, I think.
>
>
> -Doug
>
>
>
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: About RK3288 i2c scl duty cycle
2014-09-18 1:26 ` About RK3288 i2c scl duty cycle addy ke
@ 2014-09-18 4:17 ` Doug Anderson
0 siblings, 0 replies; 2+ messages in thread
From: Doug Anderson @ 2014-09-18 4:17 UTC (permalink / raw)
To: addy ke
Cc: Max Schwarz, Heiko Stübner, Wolfram Sang, Tao Huang,
Eddie Cai, linux-i2c, linux-kernel, linux-arm-kernel,
linux-rockchip
Addy,
On Wed, Sep 17, 2014 at 6:26 PM, addy ke <addy.ke@rock-chips.com> wrote:
> Add public list
>
> On 2014/9/17 23:17, Doug Anderson wrote:
>> Addy,
>>
>> On Tue, Sep 16, 2014 at 6:30 PM, addy.ke@rock-chips.com
>> <addy.ke@rock-chips.com> wrote:
>>> hi, all
>>
>> Any reason why you didn't add some public lists? It seems like this
>> is a perfect discussion for linux-i2c.
>>
>>
>>> According to i2c-bus specification(version2.1, page 32, Table5, FAST-MODE):
>>> The minimum LOW period of the scl clock is <1.3us>, and the minimum HIGH
>>> period of the scl clock is <0.6us>.
>>> T(min_low) : T(min_high) ~= 2 : 1
>>>
>>> If <DIVH = DIVL> in fast mode(scl rate = 400Khz)
>>> 1)Under ideal conditions, T(scl_low) = T(scl_high) = <1.25us>
>>> 2)Our measurement, T(scl_low) = <1.3us>, T(scl_high) = <1.25us>
>>>
>>> The low period of the scl clock is critical.
>>>
>>> Do we need set <DIVL:DIVH = 1 : 2> to increase T(scl_low)? // T(scl_low )
>>> : T(scl_High) = 2 : 1
>>
>> I can't say I've ever looked at that pat of the i2c spec before, but
>> what you say seems reasonable to me. ...well for 400kHz, at least.
>> At 100kHz you shouldn't use the same 2:1 ratio.
>
> Yes, in normal-mode(100K) we can be only used 1:1 ratio.
> But in FAST-MODE maybe we must use 2:1 ratio.
> ----
> In Table 5(Characteristics of the SDA and SCL bus lines for F/S-mode I2C-bus devices)
>
> 1)FAST-MODE(400K):
> The minimum LOW period of the scl clock 1.3us
> the minimum HIGH period of the scl clock 0.6us
> T(min_low) : T(min_high) ~= 2 : 1
>
> But I can't see any ratio about In FAST-mode(400k) and Normal-mode(100k).
> 2)Normal-MODE(100K):
> The minimum LOW period of the scl clock 4.7us
> the minimum HIGH period of the scl clock 4.0us
> T(min_low) : T(min_high) ~= 1 : 1
You might as well do the math all the way correctly. That is for
clock > 100kHz use 47 / 87 and 40 / 87. For clock <= 100kHz use 13 /
19 and 6 / 19
I think that'll give us a max margin, or (given perfect precision):
* a low of 5.4us (10 * 47 / 87.) and a high of 4.6us (10 * 40 / 87.) for 100kHz
* a low of 1.7us and a high of .8us for 400kHz
> 3) HS-mode(3.4M)
> ratio of 1 to 2 is required, decribed as follows:
> Hs-mode master devices generate a serial clock signal with a HIGH to LOW ratio of 1 to 2
You forgot about Fast Mode Plus! ;) You should probably think of
that before High Speed (IMHO)...
...seriously, though, I think you should send up a patch to do 400kHz
right first, then worry about fast mode plus and high speed. I
haven't read through the whole i2c-rk3x.c driver, but I can't quite
believe that HS mode is supported right now. It requires a whole
bunch of extra negotiation.
-Doug
^ permalink raw reply [flat|nested] 2+ messages in thread
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2014-09-18 1:26 ` About RK3288 i2c scl duty cycle addy ke
2014-09-18 4:17 ` Doug Anderson
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