39e8e58c20
Sometimes it is necessary to combine several gpio pins into an ad-hoc bus and manipulate the pins as a group. In such cases manipulating the pins individualy is not an option, because the value on the "bus" assumes potentially-invalid intermediate values as each pin is changed in turn. Note that the "bus" may be something as simple as a bi-color LED where changing colors requires changing both gpio pins at once, or something as complex as a bitbanged multiplexed address/data bus connected to a microcontroller. In addition to the absolute requirement of simultaneously changing the output values of driven pins, a desirable feature of these new methods is to provide a higher-performance mechanism for reading and writing multiple pins, especially from userland where pin-at-a-time access incurs a noticible syscall time penalty. These new interfaces are NOT intended to abstract away all the ugly details of how gpio is implemented on any given platform. In fact, to use these properly you absolutely must know something about how the gpio hardware is organized. Typically there are "banks" of gpio pins controlled by registers which group several pins together. A bank may be as small as 2 pins or as big as "all the pins on the device, hundreds of them." In the latter case, a driver might support this interface by allowing access to any 32 adjacent pins within the overall collection. Or, more likely, any 32 adjacent pins starting at any multiple of 32. Whatever the hardware restrictions may be, you would need to understand them to use this interface. In additional to defining the interfaces, two example implementations are included here, for imx5/6, and allwinner. These represent the two primary types of gpio hardware drivers. imx6 has multiple gpio devices, each implementing a single bank of 32 pins. Allwinner implements a single large gpio number space from 1-n pins, and the driver internally translates that linear number space to a bank+pin scheme based on how the pins are grouped into control registers. The allwinner implementation imposes the restriction that the first_pin argument to the new functions must always be pin 0 of a bank. Differential Revision: https://reviews.freebsd.org/D11810
FreeBSD Source:
This is the top level of the FreeBSD source directory. This file
was last revised on:
FreeBSD
For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information).
The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree. See build(7) and http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html for more information, including setting make(1) variables.
The buildkernel and installkernel targets build and install
the kernel and the modules (see below). Please see the top of
the Makefile in this directory for more information on the
standard build targets and compile-time flags.
Building a kernel is a somewhat more involved process. See build(7), config(8), and http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html for more information.
Note: If you want to build and install the kernel with the
buildkernel and installkernel targets, you might need to build
world before. More information is available in the handbook.
The kernel configuration files reside in the sys/<arch>/conf
sub-directory. GENERIC is the default configuration used in release builds.
NOTES contains entries and documentation for all possible
devices, not just those commonly used.
Source Roadmap:
bin System/user commands.
cddl Various commands and libraries under the Common Development
and Distribution License.
contrib Packages contributed by 3rd parties.
crypto Cryptography stuff (see crypto/README).
etc Template files for /etc.
gnu Various commands and libraries under the GNU Public License.
Please see gnu/COPYING* for more information.
include System include files.
kerberos5 Kerberos5 (Heimdal) package.
lib System libraries.
libexec System daemons.
release Release building Makefile & associated tools.
rescue Build system for statically linked /rescue utilities.
sbin System commands.
secure Cryptographic libraries and commands.
share Shared resources.
sys Kernel sources.
tests Regression tests which can be run by Kyua. See tests/README
for additional information.
tools Utilities for regression testing and miscellaneous tasks.
usr.bin User commands.
usr.sbin System administration commands.
For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/synching.html