With a broken device, or a broken interface circuit, it is possible
for _ow_read_byte() to spin forever. This patch arranges for it to
timeout after 5 seconds if it cannot read a valid byte from the UART.
Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
This commit introduces support for Dallas Semiconductor (DS) 1-wire
compliant device support using an available UART device.
The principle of operation is described in the following Application
note by Maxim Electronics:
https://www.maximintegrated.com/en/app-notes/index.mvp/id/214
with help (1-wire search) from:
https://www.maximintegrated.com/en/app-notes/index.mvp/id/187
It has been tested on Galileo 2 and Edison, with 2 DS 1-wire devices,
the DS18B20 and DS2413 connected to the bus. A UPM driver for the
DS2413 is already complete and a PR will be submitted after this one.
It is important that you use a UART with CMOS/TTL level voltages
(3.3v/5v) RX and TX lines. DO NOT use standard RS232 level voltages
or you are going to have a bad day.
In order for this to work, a simple interface circuit, using a single
diode must be constructed:
(forgive my "Asciihematic" :)
-|
U|
A| TX---|<--+
R| |
T| RX-------o--------o 1-wire data bus
-|
The diode on TX is a 1N4148 (cheap and common), with the cathode
connected to TX, and the anode connected to RX and the 1-wire data
line.
The 1-wire data line requires a pull-up resistor, as the DS 1-wire
spec requires. 4.7-5K is typical for DS 1-wire buses.
NOTE: DHT-type (temp/humidity sensor) 1-wire devices ARE NOT DS 1-wire
compliant, and will not work with this code/circuit unfortunately.
Also note, this will use up one of your UARTs, which cannot be used
for any other purpose (ie: to access true UART-type serial devices).
You can however, connect as many DS 1-wire devices as feasible to this
UART, as it will function as a DS 1-wire bus master.
Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
