Linux <-> Olimex GPIO mapping on Micro

Started by KD6PAG, January 17, 2014, 11:36:43 pm

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KD6PAG

I tried to use a GPIO pin documented in the iMX233-OLINUXINO-MICRO
without success and noting postings about GPIO pins in the forum,
so i determined by experiment what the pin maps are, for my board
at least.

I wrote a PERL program to determine the mapping between Linux GPIO
pins and the CON1/CON2 pads on the OLinuXino Micro board.  I picked
a pin that i knew worked as a sense pin and used to check the other
pads.  For each pad, in turn, i made each of the GPIO lines that
Linux would allow me to write into an output.  I read the sense pin
immediately after doing that, and then after writing a "0" and a "1".
The results were consistent for many pads, and for most documented
pads, only one GPIO pin (that Linux knew about) would affect that
pad.  A few documented did not respond to any Linux pins and those
are enclosed in [].  One pin of those responded before this testing
and it is enclosed in ().


    L3      32
    L4      33
    L5      34
    L6      35
    L7      36
    L8      37
    L9      38      R9      [20]
    L10     39
    L11     [0]
    L12     1
    L13     2
    L14     [3]
    L15     4
    L16     5
    L17     6
    L18     7
    L19     16
    L20     [17]
    L21     54
    L22     57
    L23     56
    L24     55      R24     92
    L25     50      R25     91
    L26     52      R26     23
    L27     51      R27     (25)
    L28     53      R28     60

    Unreadable: 17, 65


Sorted by Linux pin number, to match the Olimex documentation, we have:

    0       [L11]
    1       L12
    2       L13
    3       [L14]
    4       L15
    5       L16
    6       L17
    7       L18
    16      L19
    17      [L20]
    20      [R9]
    23      R26
    25      (R27)
    32*     L3
    33*     L4
    34*     L5
    35*     L6
    36*     L7
    37*     L8
    38*     L9
    39*     L10
    50*     L25
    51      L27
    52      L26
    53      L28
    54*     L21
    55      L24
    56      L23
    57*     L22
    60*     R28
    91      R25
    92      R24


Pins with "*" are not in Revision J of the documentation (January 2013).
Linux pins 32:39 are documented as being used by the LCD, which i have
not compiled into my kernel, so they might not be usable as GPIO lines
if you have that feature enabled.

Doing this allowed me to select two pins which will suit our application
and were not in the original documentation.  I hope this is helpful to
someone else as well.