5 Replies Latest reply on Jun 15, 2017 1:19 PM by Intel Corporation

    /dev/ttyMFD1, pin 0 (rx, gpio 130), pin 1 (tx, gpio 131)




      If you are new to this GPIO stuff read the following:



      I am trying to echo text to /dev/ttyMFD1 and use cat /dev/ttyMFD1 to display it, but cat doesn't show anything.


      My setup is:


          # cat /etc/version: 201606061707

          Windows 10 PC with putty installed


      This is what I have tried ...


      Step 1: Booted Edison


      Step 2: Displayed the direction file for the GPIOs associated with pin 0 (rx) and pin 1 (tx):


      Looking at /sys/class/gpio

             and /sys/kernel/debug/gpio_debug


      pin     GPIO    Direction       Value   current_pinmux  current_pullstrength


      0       130             in                    0       mode1                          2k

               216            out                  0       *no file*                      *no file*

               248           out                  0       *no file*                      *no file*


      1       131            out                  1        mode1                          50k

              217            in                     1        *no file*                      *no file*

              249           out                   1        *no file*                      *no file*


      Step 3: run the script to do the echos


      I used the code in the following:



      I changed the code so that only "in" and "out" were used.


      For my rational see my post #17 and Yermi's post #18 here:



      Step 4: Display the direction files again


      Looking at /sys/class/gpio

             and /sys/kernel/debug/gpio_debug


      pin     GPIO    Direction       Value   current_pinmux  current_pullstrength


      0       130          in                   0            mode1                   2k

               216          in                   0            *no file*                 *no file*

               248          in                   0            *no file*                 *no file*


      1       131          out                1            mode1                  50k

               217          in                  0            *no file*                 *no file*

               249          out                0            *no file*                 *no file*


      The contents of the Direction file (eg: /sys/class/gpio/gpio130/direction ) match what the echo script wanted to do.


      Step 4: Use PuTTY to open an ssh window on edison


      Step 5: In the ssh window: cat /dev/ttyMFD1


      There is no command prompt, which makes sense, since Linux is waiting for something to be displayed.


      Step 6: in the PuTTY com4 window: echo Edison > /dev/ttyMFD1




      Nothing is displayed in the PuTTY ssh window after the cat line (Step 5).


      I have spent a long time reading a bunch of discussions trying to figure out how to get this to work.


      Question: any idea what I am not doing or doing wrong?