45c1d967a7
Add a binding for a generic definition of an output GPIO that sets the
state of rs485-rx-during-tx. The idea is that the hardware already controls
the option receiving during sending before it gets to the signal receiving
hardware. The standard RS485 is a half-duplex bus that in most cases is
driven by an UART controller. The advantage of using this GPIO is that it
is independent of the capabilities of the UART core and the UART driver.
On the hardware side the interface to the bus is controlled by a transceiver,
that has a pin called RE (RX Enable) or similar, which connects the bus to
the RX signal of the UART controller. The GPIO can switch between two states
to control the RE pin via an electrical circuit:
- Active:
The RE pin is always active. The UART RX see everything on the bus and
therefore also what happens with the TX signal on the bus.
- Inactive:
The RE pin is always active, but during sending on the bus the pin RE is
inactive. So basically the receiving during sending is suppressed.
A possible circuit diagram could look like this:
┌──────────────────┐
│ RS485 │
TX ───────────────┤D │
│ Transceiver │
RTS ────┬──────────┤DE │
│ │ │
│ ┌─────┐ │ │
└─┤& │ │ │
│ ├──┤!RE │
!rx_during_tx_gpio ──────┤ │ │ │
└─────┘ │ │
│ │
RX ───────────────┤R │
│ │
└──────────────────┘
Here the RTS pin of the UART core is used to control TX via the transceiver
pin DE (Drive Enable). RE and rx_during_tx_gpio are active low.
Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221202104127.122761-1-cniedermaier@dh-electronics.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
|
||
|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.