Pretty funny that there are 2 Robert Berger’s with the same question! But thanks a lot Mirko for the explanation. That may help my situation as we do have the opportunity to add some hardware.
I did find a way to do parallel writes to the GPIO by doing direct access of the GPIO registers instead of going the the /sysfs filesystem access. Unfortunately I could not find a way to do this with Ruby without creating a C extension. (I spent all day yesterday trying! Looks like the existing mmap gems for ruby are all obsolete and don’t work with Ruby 2.x and/or won't map in /dev/mem) A good description of the solution is at http://elinux.org/EBC_Exercise_11b_gpio_via_mmap It has some C examples of how to do it natively and shows how you can use devmem2 to do it in the shell command line. For Ruby if you’re update rate was low, you could shell out to devmem2 to do parallel writes: For instance to get the 32bit value (that’s how big the registers are) at 0x4804c13c value = `devmem2 0x4804c13c ` That would show you what the bits are for gpio1 To clear the bits in the pattern 0x01000000 in the GPIO_CLEARDATAOUT register result = `devmem2 0x4804c190 w 0x01000000` That would turn the USR3 LED off if it was on To set the bit pattern in GPIO_SETDATAOUT (0x194) register result = `devmem2 0x4804c194 w 0x01000000` That would turn the USR3 LED on To turn on USR1 and USR 3 at the same time: result = `devmem2 0x4804c194 w 0x01400000` You could do the same to a group of other gpio pins as long as they are all on the gpio 32 bit register Getting devmem2 Turns out that devmem2 is not a Debian package (though it is an Ubuntu package) but you can get the source at http://www.lartmaker.nl/lartware/port/devmem2.c and compile and install it with: gcc devmem2.c -o devmem2 chmod a+x devmem2 mv devmem2 /usr/local/bin __________________________________ Robert J Berger +1 408-838-8896 Internet Bandwidth Development, LLC http://www.linkedin.com/in/rberger On Jul 14, 2014, at 10:59 AM, Mirko Fucci <[email protected]> wrote: > > Ok Robert, i will try to explain how i solved my problem, apologise me if > something is not clear but i am not an expert and i beg anyone to correct me > if i say something wrong. > I2C is a serial protocol and is fully supported by BBB so you can set output > pins (8 pins) of MCP23008 setting a chip's register once the chip is > connected and initialized. When you set your output serial data all chip's > output pins are set at the same time (because there is an internal > synchronized register). > > So, if you need to set 4 pins with 1101 you can set chip's register with > 00001101 value e then you find the value 1101 at the chip's output pins. > > You don't need to set your GPIO to use the MCP23008 because P9_19 (CLK) and > P9_20 (SDA) are already set to work with I2C protocol (at least in debian > Wheezy) and all you need is assign an unique address (connecting address pins > to GND or VCC) to every MCP23008 chip you connect to these pins (is a bus). > > Take a look at these links, i think i started from there : > http://embedded-lab.com/blog/?p=2834 > http://www.gigamegablog.com/2012/11/04/beaglebone-coding-101-i2c/ > > > > > > > > 2014-07-14 18:43 GMT+02:00 robert.berger <[email protected]>: > Hi, > > > On Monday, July 14, 2014 4:13:13 PM UTC+3, Mirko Fucci wrote: > Yes, but for me the simplest way was using a port expander (i used MCP23008) > through I2C Interface, very simple to handle with BBB. > > Can you please elaborate a bit more on what you tried? > > With the standard GPIO framework [1] I am not sure you can do what you want. > There was an attempt to add block gpio [2] but I don't think this made it > into mainline. > > Regards, > > Robert > > [1] http://lwn.net/Articles/532714/ > [2] http://lwn.net/Articles/533632/ > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to a topic in the Google > Groups "BeagleBoard" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/beagleboard/6sWV16b0a5Y/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > For more options, visit https://groups.google.com/d/optout. > > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to a topic in the Google > Groups "BeagleBoard" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/beagleboard/6sWV16b0a5Y/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > For more options, visit https://groups.google.com/d/optout.
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