Date: Mon, 20 Aug 2018 11:13:08 +0300 From: Daniel Braniss <danny@cs.huji.ac.il> To: Ian Lepore <ian@freebsd.org> Cc: Rajesh Kumar <rajfbsd@gmail.com>, freebsd-hackers@freebsd.org, freebsd-drivers@freebsd.org Subject: Re: Need a clarification regarding I2C bus frequency in FreeBSD Message-ID: <A8202939-328A-4564-9CF5-F5F66F68B7B0@cs.huji.ac.il> In-Reply-To: <BF721728-B6F5-4214-9180-B911D32D9FCA@cs.huji.ac.il> References: <CAAO%2BANOXwXAzJt%2BBZez6422jqKjrKPboSe_%2BudnOCWxYqE-=sQ@mail.gmail.com> <1534523216.27158.17.camel@freebsd.org> <CAAO%2BANOs_YVov-d21Em1EHzajQw7wHsxkzZCnsZwkfBr2=mEiA@mail.gmail.com> <1534702861.27158.36.camel@freebsd.org> <BF721728-B6F5-4214-9180-B911D32D9FCA@cs.huji.ac.il>
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> On 20 Aug 2018, at 09:49, Daniel Braniss <danny@cs.huji.ac.il> wrote: > > > >> On 19 Aug 2018, at 21:21, Ian Lepore <ian@freebsd.org <mailto:ian@freebsd.org>> wrote: >> >> On Sun, 2018-08-19 at 19:23 +0530, Rajesh Kumar wrote: >>> Hi Ian, >>> >>> Basically, I want to set the I2C clock frequency for Designware IP in our >>> board to 150Mhz. So, I was looking for the way in FreeBSD. >>> >>> So, Is this the frequency which is configured through the clock high/low >>> registers? I see the those register are coded to 100 and 125 currently, I >>> am not sure how that value is arrived. If it needs to be configured for >>> 150Mhz, how to derive the appropriate values? I looked at the DW_apb_i2c >>> databook section 3.11 to understand about it. I am still unclear. I see a >>> comment saying "Program based on 25000 Hz clock". In my case, should they >>> be programmed based on 150Mhz clock? >> >> Rajesh, >> >> Please bottom-post when replying on freebsd mailing lists, mixed top- >> and bottom-posting is too confusing. >> >> What exactly do you mean when you say "the i2c clock frequency"? >> >> The datasheet appears to use a term like that to refer to the internal >> clock used to drive the IP block in the chip. That base clock is then >> divided down to create the i2c bus frequency on the I2C_SCL line. >> >> The IG4_REG_SS_SCL_HCNT and IG4_REG_SS_SCL_LCNT registers are the >> duration in base clock ticks that the SCL line is held high and low for >> standard speed. The registers with FS in the name are for high speed >> mode. >> >> The comment block and the values our driver programs into those >> registers appear to be wildly wrong. There is no way a base clock >> running at 25KHz can be divided down to create i2c bus speeds of 100KHz >> and 400KHz for standard and fast modes. If the base clock really is >> 25KHz then the driver currently sets the i2c bus to run at 111Hz. >> >> The hardware default values for the HCNT/LCNT registers, as given in >> the datasheet referenced by the driver [1], would be consistant with an >> internal base clock speed of 1GHz. The fact that the header file >> defines a IG4_REG_CLK_PARMS register, but the datasheet doesn't mention >> it, makes me think that on some versions of the hardware the speed is >> fixed and the driver has to know what that is based on the version, or >> vendor, or something. Other versions of the hardware may have >> information about the base clock speed in that IG4_REG_CLK_PARMS >> register. >> >> What we need is for someone who has this hardware to put an >> oscilliscope on the SCL line and get us some real-world truth. >> >> [1] http://www.intel.com/content/www/us/en/processors/core/4th-gen-core-family-mobile-i-o-datasheet.html?wapkw=datasheets+4th+generation <http://www.intel.com/content/www/us/en/processors/core/4th-gen-core-family-mobile-i-o-datasheet.html?wapkw=datasheets+4th+generation><http://www.intel.com/content/www/us/en/processors/core/4th-gen-core-family-mobile-i-o-datasheet.html?wapkw=datasheets+4th+generation <http://www.intel.com/content/www/us/en/processors/core/4th-gen-core-family-mobile-i-o-datasheet.html?wapkw=datasheets+4th+generation>>; >> >> -- Ian > > > hi, > I have similar issues with the allwinner/twsi but I do have a Saleae Logic and here is a nice picture: ah, maybe this is better: https://cs.huji.ac.il/~danny/Screen%20Shot%202018-08-20%20at%2011.06.43.png > > > > danny > > _______________________________________________ > freebsd-hackers@freebsd.org <mailto:freebsd-hackers@freebsd.org> mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers <https://lists.freebsd.org/mailman/listinfo/freebsd-hackers>; > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org <mailto:freebsd-hackers-unsubscribe@freebsd.org>"
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