Kernel driver w1-uart

UART timing 기반 1-Wire

`w1-uart`는 Serial Device Bus를 통해 UART interface를 사용해 1-Wire timing pattern을 만드는 bus driver이며 원 저자는 Christoph Winklhofer입니다.

동작 방식은 Analog Devices의 'Using a UART to Implement a 1-Wire Bus Master' 문서를 따릅니다.

UART peripheral은 full-duplex와 open-drain mode를 지원해야 합니다.

Baud rate와 transmitted byte 조합이 1-Wire read bit, write bit, reset pulse에 해당하는 timing pattern을 만듭니다.

.. SPDX-License-Identifier: GPL-2.0-or-later

=====================
Kernel driver w1-uart
=====================

Author: Christoph Winklhofer <[email protected]>


Description
-----------

UART 1-Wire bus driver. The driver utilizes the UART interface via the
Serial Device Bus to create the 1-Wire timing patterns as described in
the document `"Using a UART to Implement a 1-Wire Bus Master"`_.

.. _"Using a UART to Implement a 1-Wire Bus Master": https://www.analog.com/en/technical-articles/using-a-uart-to-implement-a-1wire-bus-master.html

In short, the UART peripheral must support full-duplex and operate in
open-drain mode. The timing patterns are generated by a specific

Reset·presence·bit timing

Reset과 presence detect는 9600 baud, 즉 bit당 104.2us를 사용합니다.

UART는 least-significant bit first이며 low start bit 뒤 `0xf0`을 보내 1-Wire reset low time 521us를 만듭니다.

1-Wire device가 존재하면 line을 low로 끌어 received byte를 바꾸고 driver는 이 차이로 presence를 판단합니다.

Read/write bit는 115200 baud, bit당 8.7us를 사용합니다.

`0x80`은 low time 69.6us의 Write-0, `0xff`는 low time 8.7us의 Read-0, Read-1, Write-1에 사용됩니다.

기본 baud는 reset/presence 9600, read/write 115200입니다. 실제 baud가 요청 값과 다르면 transmitted byte를 조정해 같은 1-Wire timing을 만듭니다.

combination of baud-rate and transmitted byte, which corresponds to a
1-Wire read bit, write bit or reset pulse.

For instance the timing pattern for a 1-Wire reset and presence detect uses
the baud-rate 9600, i.e. 104.2 us per bit. The transmitted byte 0xf0 over
UART (least significant bit first, start-bit low) sets the reset low time
for 1-Wire to 521 us. A present 1-Wire device changes the received byte by
pulling the line low, which is used by the driver to evaluate the result of
the 1-Wire operation.

Similar for a 1-Wire read bit or write bit, which uses the baud-rate
115200, i.e. 8.7 us per bit. The transmitted byte 0x80 is used for a
Write-0 operation (low time 69.6us) and the byte 0xff for Read-0, Read-1
and Write-1 (low time 8.7us).

The default baud-rate for reset and presence detection is 9600 and for
a 1-Wire read or write operation 115200. In case the actual baud-rate
is different from the requested one, the transmitted byte is adapted
to generate the 1-Wire timing patterns.

Device tree 사용

UART 1-Wire bus는 serial node, 예를 들어 `uart0` 아래에 단일 `onewire` child를 추가해 device tree에 지정합니다.

Child node의 `compatible`은 `w1-uart`입니다.

이 binding으로 Serial Device Bus가 UART controller와 1-Wire master driver를 연결합니다.

Usage
-----

Specify the UART 1-wire bus in the device tree by adding the single child
onewire to the serial node (e.g. uart0). For example:
::

  @uart0 {
    ...
    onewire {
      compatible = "w1-uart";
    };
  };