Date: Mon, 17 Nov 2014 13:47:45 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-arm@FreeBSD.org Subject: [Bug 195009] [patch]: [arm] Use 400 kHz as the default OMAP4 I2C bus speed Message-ID: <bug-195009-7-xK6F4AKLpo@https.bugs.freebsd.org/bugzilla/> In-Reply-To: <bug-195009-7@https.bugs.freebsd.org/bugzilla/> References: <bug-195009-7@https.bugs.freebsd.org/bugzilla/>
next in thread | previous in thread | raw e-mail | index | archive | help
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=195009 Luiz Otavio O Souza,+55 (14) 99772-1255 <loos@FreeBSD.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |loos@FreeBSD.org --- Comment #2 from Luiz Otavio O Souza,+55 (14) 99772-1255 <loos@FreeBSD.org> --- (In reply to Scott Ellis from comment #0) > The I2C bus speed for OMAP4 boards defaults to 842 kHz. > > The formula for calculating this comes from the TRM table 23-8 > > scl = i2c_fclk / ( ( psc + 1) * ( (scll + 7) + (sclh + 5) ) ) > > The code says it's attempting 1 MHz, but it's using the wrong values. Yes, that is right. These values comes from TRM table 23-9 in "Fast Mode+". The TRM doesn't take into account the '+ 1' for the prescaler value (psc), but only for Fast Mode+, all the other values seems correct. For a internal clock frequency of 19.2 MHz we need to set the prescaler to 4: 96 MHz / (4 + 1) = 19.2 MHz And then the bus frequency is: 19.2 MHz / (3 + 7) + (4 + 5) = 1.010 MHz Good catch! Thanks! -- You are receiving this mail because: You are the assignee for the bug.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bug-195009-7-xK6F4AKLpo>