Add public list On 2014/9/17 23:17, Doug Anderson wrote: > Addy, > > On Tue, Sep 16, 2014 at 6:30 PM, addy.ke@xxxxxxxxxxxxxx > <addy.ke@xxxxxxxxxxxxxx> 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 > > > -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
