GPIO(3) (SA1100) GPIO(3)
NAME
gpio - access to GPIO registers
SYNOPSIS
bind -a #G /dev
/dev/gpioclear
/dev/gpioctl
/dev/gpioedge
/dev/gpioset
/dev/gpiostatus
DESCRIPTION
The GPIO interface serves a one-level directory with five
files that give access to the GPIO registers in the SA1100.
See the SA1100 handbook for details of the function of the
various registers.
The control file gpioctl accepts commands to set individual
bits in the edge detect registers. Each control message has
three space-separated fields:
reg pin value
where reg is a single character denoting a register, pin a
bit within it, and val the value (0 or 1) for that bit.
Valid choices for reg are: d (GPDR), r (GRER), f (GFER), and
a (GAFR). For example, the control message
d 10 1
sets bit 10 (following the handbook's bit-numbering conven-
tions) in the GPIO pin direction register GPDR.
The read-only file gpiostatus shows the names and values (in
hexadecimal) of all GPIO registers.
The remaining data files allow bits to be read by Sys->read
requests and set by Sys->write requests. When read, each
file returns the value of a given register as a single 8
digit hexadecimal number: gpioset and gpioclear both give
the value of the level register, GPLR; and gpioedge gives
the value of the edge dectect register, GEDR. Each write
request should present a single number in textual form,
which is assumed to be hexadecimal by default. The value is
written to a GPIO register: gpioset corresponds to GPSR,
gpioclear corresponds to GPCR, and gpioedge corresponds to
GEDR.
SOURCE
Page 1 Plan 9 (printed 12/22/24)
GPIO(3) (SA1100) GPIO(3)
/os/sa1100/devgpio.c
Page 2 Plan 9 (printed 12/22/24)