Date: Fri, 19 Apr 2019 09:59:14 -0600 From: Ian Lepore <ian@freebsd.org> To: Daniel Braniss <danny@cs.huji.ac.il> Cc: "freebsd-arm@freebsd.org" <arm@freebsd.org> Subject: Re: i2c almost working for me, was Re: i2c still not working for me Message-ID: <e0aa9eba353f496b51006add4510d9b9c42bfbc6.camel@freebsd.org> In-Reply-To: <CD499934-6E4E-4416-9B73-F3B8AB9A916D@cs.huji.ac.il> References: <12F641C3-9FAA-4A3A-BA18-A7302F3A0F5E@cs.huji.ac.il> <20190409095819.c560dbc156c46e5ca0244e3e@bidouilliste.com> <23A47048-642A-481C-B7BE-B61E55F82955@cs.huji.ac.il> <20190409171604.GA4581@bluezbox.com> <FCA4E00E-455A-46BF-AD78-E20E1E997BFC@cs.huji.ac.il> <6119CE3B-6042-4DDC-82BE-B0C0C7ADA838@cs.huji.ac.il> <5D4799BC-08DF-4F3D-81A4-C2D938F4AF93@cs.huji.ac.il> <20190417222601.c037efe0cb48987c81032bac@bidouilliste.com> <DDDAC739-D68F-4843-BF89-3044ED442F69@cs.huji.ac.il> <64b5598e2c8c7265f89a31b1f191cb1be318788a.camel@freebsd.org> <CD499934-6E4E-4416-9B73-F3B8AB9A916D@cs.huji.ac.il>
next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, 2019-04-19 at 10:20 +0300, Daniel Braniss wrote: > > > > You can often compensate for a too-long cable by adding some stronger > > pullups. It's typical for a SOM to have pullups in the 4.7K range on > > i2c. You can add your own 1K pullups to see if that helps the rise > > times on the bus. > > well, at the moment it works ok with a 6m cable, i’ll try your suggestion soon. Wow, I'm surprised that works; when you said "long" I was thinking something like 1m. You might need some sort of active helper device, something like a TI txs0104e that has rise-time accellerators built in. Or, maybe you could just slow the bus down enough to allow for the rise/fall times on that big a capacitive load, like run the bus at 10 or 20khz instead of 100. -- Ian
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?e0aa9eba353f496b51006add4510d9b9c42bfbc6.camel>