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Julius Werner 1732dcb90c drivers/uart: Add helper function to allow bit-banging
In some cases it may be useful to be able to bitbang a UART, such as
during early bring-up when a driver for the actual controller isn't
available yet. On some platforms we may even want to use this
permanently, such as on the SDM845 where the hardware UART controller
needs to have firmware loaded and is thus unavailable for most of the
bootblock.

This patch adds some helper code that makes it easy to implement this on
a platform, you just have to pass it a function to control the Tx pin
state and it will do the rest. It relies on the mono_time API and is
thus bound to microsecond timing granularity, but that seems to be
barely good enough for 115200 baud if the bit times are calculated
carefully.

Change-Id: If7dcecc7b8a95ec15f456efd2ec1f1e0dde239b4
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/25812
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
2018-04-26 01:19:13 +00:00
3rdparty 3rdparty/libgfxinit: Update submodule pointer 2018-04-13 16:42:48 +00:00
Documentation Documentation/timestamp.md: Fix markdown formatting 2018-04-17 17:18:23 +00:00
configs configs: Add intel/harcuvar FSP 2.0 sample configuration 2017-10-04 02:56:33 +00:00
payloads libpayload: Move GDB functions to stdlib.h 2018-04-19 20:39:29 +00:00
src drivers/uart: Add helper function to allow bit-banging 2018-04-26 01:19:13 +00:00
util util/riscvtools: Rename to util/riscv/ 2018-04-25 11:43:20 +00:00
.checkpatch.conf .checkpatch.conf: Ignore CORRUPTED_PATCH lint 2017-10-29 10:11:58 +00:00
.clang-format clang-format: Update .clang-format to be compliant with linux kernel coding style 2018-04-23 09:26:08 +00:00
.gitignore util/blobtool: rename to bincfg 2018-01-18 13:47:20 +00:00
.gitmodules Set up 3rdparty/libgfxinit 2016-10-29 01:35:03 +02:00
.gitreview
COPYING
MAINTAINERS MAINTAINERS: change second PC Engines maintainer 2018-03-21 18:25:49 +00:00
Makefile Makefile: Add filelist to help 2018-01-29 15:35:11 +00:00
Makefile.inc device: Include devicetree in SMM stage 2018-02-22 09:55:19 +00:00
README README: Update requirements 2017-06-27 17:04:32 +00:00
gnat.adc
toolchain.inc toolchain: Always use GCC for Ada sources 2017-09-23 10:57:40 +00:00

README

-------------------------------------------------------------------------------
coreboot README
-------------------------------------------------------------------------------

coreboot is a Free Software project aimed at replacing the proprietary BIOS
(firmware) found in most computers.  coreboot performs a little bit of
hardware initialization and then executes additional boot logic, called a
payload.

With the separation of hardware initialization and later boot logic,
coreboot can scale from specialized applications that run directly
firmware, run operating systems in flash, load custom
bootloaders, or implement firmware standards, like PC BIOS services or
UEFI. This allows for systems to only include the features necessary
in the target application, reducing the amount of code and flash space
required.

coreboot was formerly known as LinuxBIOS.


Payloads
--------

After the basic initialization of the hardware has been performed, any
desired "payload" can be started by coreboot.

See https://www.coreboot.org/Payloads for a list of supported payloads.


Supported Hardware
------------------

coreboot supports a wide range of chipsets, devices, and mainboards.

For details please consult:

 * https://www.coreboot.org/Supported_Motherboards
 * https://www.coreboot.org/Supported_Chipsets_and_Devices


Build Requirements
------------------

 * make
 * gcc / g++
   Because Linux distribution compilers tend to use lots of patches. coreboot
   does lots of "unusual" things in its build system, some of which break due
   to those patches, sometimes by gcc aborting, sometimes - and that's worse -
   by generating broken object code.
   Two options: use our toolchain (eg. make crosstools-i386) or enable the
   ANY_TOOLCHAIN Kconfig option if you're feeling lucky (no support in this
   case).
 * iasl (for targets with ACPI support)
 * pkg-config
 * libssl-dev (openssl)

Optional:

 * doxygen (for generating/viewing documentation)
 * gdb (for better debugging facilities on some targets)
 * ncurses (for 'make menuconfig' and 'make nconfig')
 * flex and bison (for regenerating parsers)


Building coreboot
-----------------

Please consult https://www.coreboot.org/Build_HOWTO for details.


Testing coreboot Without Modifying Your Hardware
------------------------------------------------

If you want to test coreboot without any risks before you really decide
to use it on your hardware, you can use the QEMU system emulator to run
coreboot virtually in QEMU.

Please see https://www.coreboot.org/QEMU for details.


Website and Mailing List
------------------------

Further details on the project, a FAQ, many HOWTOs, news, development
guidelines and more can be found on the coreboot website:

  https://www.coreboot.org

You can contact us directly on the coreboot mailing list:

  https://www.coreboot.org/Mailinglist


Copyright and License
---------------------

The copyright on coreboot is owned by quite a large number of individual
developers and companies. Please check the individual source files for details.

coreboot is licensed under the terms of the GNU General Public License (GPL).
Some files are licensed under the "GPL (version 2, or any later version)",
and some files are licensed under the "GPL, version 2". For some parts, which
were derived from other projects, other (GPL-compatible) licenses may apply.
Please check the individual source files for details.

This makes the resulting coreboot images licensed under the GPL, version 2.