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Commit 6cd15974 authored by David Fries's avatar David Fries Committed by Linus Torvalds
Browse files

W1: feature, w1_therm.c use strong pullup and documentation 



Added strong pullup to thermal sensor driver and general documentation on
the sensor.

Signed-off-by: default avatarDavid Fries <david@fries.net>
Signed-off-by: default avatarEvgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6a158c0d

Documentation/w1/00-INDEX

+2 −0
Original line number Diff line number Diff line 
00-INDEX

	- This file

slaves/

	- Drivers that provide support for specific family codes.

masters/

	- Individual chips providing 1-wire busses.

w1.generic

Documentation/w1/slaves/00-INDEX

0 → 100644
+4 −0
Original line number Diff line number Diff line 
00-INDEX

	- This file

w1_therm

	- The Maxim/Dallas Semiconductor ds18*20 temperature sensor.

Documentation/w1/slaves/w1_therm

0 → 100644
+41 −0
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Kernel driver w1_therm

====================



Supported chips:

  * Maxim ds18*20 based temperature sensors.



Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru>





Description

-----------



w1_therm provides basic temperature conversion for ds18*20 devices.

supported family codes:

W1_THERM_DS18S20	0x10

W1_THERM_DS1822		0x22

W1_THERM_DS18B20	0x28



Support is provided through the sysfs w1_slave file.  Each open and

read sequence will initiate a temperature conversion then provide two

lines of ASCII output.  The first line contains the nine hex bytes

read along with a calculated crc value and YES or NO if it matched.

If the crc matched the returned values are retained.  The second line

displays the retained values along with a temperature in millidegrees

Centigrade after t=.



Parasite powered devices are limited to one slave performing a

temperature conversion at a time.  If none of the devices are parasite

powered it would be possible to convert all the devices at the same

time and then go back to read individual sensors.  That isn't

currently supported.  The driver also doesn't support reduced

precision (which would also reduce the conversion time).



The module parameter strong_pullup can be set to 0 to disable the

strong pullup or 1 to enable.  If enabled the 5V strong pullup will be

enabled when the conversion is taking place provided the master driver

must support the strong pullup (or it falls back to a pullup

resistor).  The DS18b20 temperature sensor specification lists a

maximum current draw of 1.5mA and that a 5k pullup resistor is not

sufficient.  The strong pullup is designed to provide the additional

current required.

drivers/w1/slaves/w1_therm.c

+13 −2
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@@ -37,6 +37,14 @@ MODULE_LICENSE("GPL"); 
MODULE_AUTHOR("Evgeniy Polyakov <johnpol@2ka.mipt.ru>");

MODULE_DESCRIPTION("Driver for 1-wire Dallas network protocol, temperature family.");



/* Allow the strong pullup to be disabled, but default to enabled.

 * If it was disabled a parasite powered device might not get the require

 * current to do a temperature conversion.  If it is enabled parasite powered

 * devices have a better chance of getting the current required.

 */

static int w1_strong_pullup = 1;

module_param_named(strong_pullup, w1_strong_pullup, int, 0);



static u8 bad_roms[][9] = {

				{0xaa, 0x00, 0x4b, 0x46, 0xff, 0xff, 0x0c, 0x10, 0x87},

				{}
@@ -192,8 +200,11 @@ static ssize_t w1_therm_read_bin(struct kobject *kobj, 
			int count = 0;

			unsigned int tm = 750;



			/* 750ms strong pullup (or delay) after the convert */

			if (w1_strong_pullup)

				w1_next_pullup(dev, tm);

			w1_write_8(dev, W1_CONVERT_TEMP);



			if (!w1_strong_pullup)

				msleep(tm);



			if (!w1_reset_select_slave(sl)) {