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Gpio serves a single file that provides access to the GPIO pins
on the Raspberry Pi. Reads from the file receive a 16–character
hexadecimal string representing a vlong giving the values of up
to 64 GPIO lines. (The processor on both the first and second
generation Pis provides 54 actual GPIO lines.) The proper method
for sampling GPIO 27 is as follows:
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read(gfd, buf, 16);
buf[16] = 0;
gvals = strtoull(buf, nil, 16);
pin27 = gvals & (1 << 27);
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Writes to gpio control the characteristics and output values of
GPIO lines. The exact operation is specified by one of the following
commands:
function pin f
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Set the function of GPIO pin to f. The valid values for f are:
in, out, alt0, alt1, alt2, alt3, alt4, atl5, and pulse. The functions
in and out set the specified GPIO line to be a general purpose
input and output, respectively. The various altn functions are
as specified in the Broadcom
documentation and differ on a per–pin basis. The pulse function
is somewhat specialized. It causes the pin to be set to an output
for 2μS and then to be set to a input. With the value of the line
set to 0 and a pullup resistor on the line, this operation provides
a short low pulse suitable for bit–banging a 1–wire
interface.
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pullup pin
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Enables the internal pullup resistor for the specified GPIO pin.
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pulldown pin
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Enables the internal pulldown resistor for the specified GPIO
pin.
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float pin
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Disables both internal pullup and pulldown resistors for the specified
GPIO pin.
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set pin value
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For GPIO pins set to the output function, this command sets the
output value for the pin. The value should be either 0 or 1.
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