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Based on kernel version 2.6.33. Page generated on 2010-02-24 15:36 EST.

1	Kernel driver lm90
2	==================
3	
4	Supported chips:
5	  * National Semiconductor LM90
6	    Prefix: 'lm90'
7	    Addresses scanned: I2C 0x4c
8	    Datasheet: Publicly available at the National Semiconductor website
9	               http://www.national.com/pf/LM/LM90.html
10	  * National Semiconductor LM89
11	    Prefix: 'lm89' (no auto-detection)
12	    Addresses scanned: I2C 0x4c and 0x4d
13	    Datasheet: Publicly available at the National Semiconductor website
14	               http://www.national.com/mpf/LM/LM89.html
15	  * National Semiconductor LM99
16	    Prefix: 'lm99'
17	    Addresses scanned: I2C 0x4c and 0x4d
18	    Datasheet: Publicly available at the National Semiconductor website
19	               http://www.national.com/pf/LM/LM99.html
20	  * National Semiconductor LM86
21	    Prefix: 'lm86'
22	    Addresses scanned: I2C 0x4c
23	    Datasheet: Publicly available at the National Semiconductor website
24	               http://www.national.com/mpf/LM/LM86.html
25	  * Analog Devices ADM1032
26	    Prefix: 'adm1032'
27	    Addresses scanned: I2C 0x4c and 0x4d
28	    Datasheet: Publicly available at the ON Semiconductor website
29	               http://www.onsemi.com/PowerSolutions/product.do?id=ADM1032
30	  * Analog Devices ADT7461
31	    Prefix: 'adt7461'
32	    Addresses scanned: I2C 0x4c and 0x4d
33	    Datasheet: Publicly available at the ON Semiconductor website
34	               http://www.onsemi.com/PowerSolutions/product.do?id=ADT7461
35	  * Maxim MAX6646
36	    Prefix: 'max6646'
37	    Addresses scanned: I2C 0x4d
38	    Datasheet: Publicly available at the Maxim website
39	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
40	  * Maxim MAX6647
41	    Prefix: 'max6646'
42	    Addresses scanned: I2C 0x4e
43	    Datasheet: Publicly available at the Maxim website
44	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
45	  * Maxim MAX6648
46	    Prefix: 'max6646'
47	    Addresses scanned: I2C 0x4c
48	    Datasheet: Publicly available at the Maxim website
49	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
50	  * Maxim MAX6649
51	    Prefix: 'max6646'
52	    Addresses scanned: I2C 0x4c
53	    Datasheet: Publicly available at the Maxim website
54	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
55	  * Maxim MAX6657
56	    Prefix: 'max6657'
57	    Addresses scanned: I2C 0x4c
58	    Datasheet: Publicly available at the Maxim website
59	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
60	  * Maxim MAX6658
61	    Prefix: 'max6657'
62	    Addresses scanned: I2C 0x4c
63	    Datasheet: Publicly available at the Maxim website
64	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
65	  * Maxim MAX6659
66	    Prefix: 'max6657'
67	    Addresses scanned: I2C 0x4c, 0x4d (unsupported 0x4e)
68	    Datasheet: Publicly available at the Maxim website
69	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
70	  * Maxim MAX6680
71	    Prefix: 'max6680'
72	    Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
73	                           0x4c, 0x4d and 0x4e
74	    Datasheet: Publicly available at the Maxim website
75	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
76	  * Maxim MAX6681
77	    Prefix: 'max6680'
78	    Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
79	                           0x4c, 0x4d and 0x4e
80	    Datasheet: Publicly available at the Maxim website
81	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
82	  * Maxim MAX6692
83	    Prefix: 'max6646'
84	    Addresses scanned: I2C 0x4c
85	    Datasheet: Publicly available at the Maxim website
86	               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
87	
88	
89	Author: Jean Delvare <khali[AT]linux-fr[DOT]org>
90	
91	
92	Description
93	-----------
94	
95	The LM90 is a digital temperature sensor. It senses its own temperature as
96	well as the temperature of up to one external diode. It is compatible
97	with many other devices, many of which are supported by this driver.
98	
99	Note that there is no easy way to differentiate between the MAX6657,
100	MAX6658 and MAX6659 variants. The extra address and features of the
101	MAX6659 are not supported by this driver. The MAX6680 and MAX6681 only
102	differ in their pinout, therefore they obviously can't (and don't need to)
103	be distinguished.
104	
105	The specificity of this family of chipsets over the ADM1021/LM84
106	family is that it features critical limits with hysteresis, and an
107	increased resolution of the remote temperature measurement.
108	
109	The different chipsets of the family are not strictly identical, although
110	very similar. For reference, here comes a non-exhaustive list of specific
111	features:
112	
113	LM90:
114	  * Filter and alert configuration register at 0xBF.
115	  * ALERT is triggered by temperatures over critical limits.
116	
117	LM86 and LM89:
118	  * Same as LM90
119	  * Better external channel accuracy
120	
121	LM99:
122	  * Same as LM89
123	  * External temperature shifted by 16 degrees down
124	
125	ADM1032:
126	  * Consecutive alert register at 0x22.
127	  * Conversion averaging.
128	  * Up to 64 conversions/s.
129	  * ALERT is triggered by open remote sensor.
130	  * SMBus PEC support for Write Byte and Receive Byte transactions.
131	
132	ADT7461:
133	  * Extended temperature range (breaks compatibility)
134	  * Lower resolution for remote temperature
135	
136	MAX6657 and MAX6658:
137	  * Better local resolution
138	  * Remote sensor type selection
139	
140	MAX6659:
141	  * Better local resolution
142	  * Selectable address
143	  * Second critical temperature limit
144	  * Remote sensor type selection
145	
146	MAX6680 and MAX6681:
147	  * Selectable address
148	  * Remote sensor type selection
149	
150	All temperature values are given in degrees Celsius. Resolution
151	is 1.0 degree for the local temperature, 0.125 degree for the remote
152	temperature, except for the MAX6657, MAX6658 and MAX6659 which have a
153	resolution of 0.125 degree for both temperatures.
154	
155	Each sensor has its own high and low limits, plus a critical limit.
156	Additionally, there is a relative hysteresis value common to both critical
157	values. To make life easier to user-space applications, two absolute values
158	are exported, one for each channel, but these values are of course linked.
159	Only the local hysteresis can be set from user-space, and the same delta
160	applies to the remote hysteresis.
161	
162	The lm90 driver will not update its values more frequently than every
163	other second; reading them more often will do no harm, but will return
164	'old' values.
165	
166	PEC Support
167	-----------
168	
169	The ADM1032 is the only chip of the family which supports PEC. It does
170	not support PEC on all transactions though, so some care must be taken.
171	
172	When reading a register value, the PEC byte is computed and sent by the
173	ADM1032 chip. However, in the case of a combined transaction (SMBus Read
174	Byte), the ADM1032 computes the CRC value over only the second half of
175	the message rather than its entirety, because it thinks the first half
176	of the message belongs to a different transaction. As a result, the CRC
177	value differs from what the SMBus master expects, and all reads fail.
178	
179	For this reason, the lm90 driver will enable PEC for the ADM1032 only if
180	the bus supports the SMBus Send Byte and Receive Byte transaction types.
181	These transactions will be used to read register values, instead of
182	SMBus Read Byte, and PEC will work properly.
183	
184	Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
185	Instead, it will try to write the PEC value to the register (because the
186	SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
187	without PEC), which is not what we want. Thus, PEC is explicitly disabled
188	on SMBus Send Byte transactions in the lm90 driver.
189	
190	PEC on byte data transactions represents a significant increase in bandwidth
191	usage (+33% for writes, +25% for reads) in normal conditions. With the need
192	to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
193	two transactions will typically mean twice as much delay waiting for
194	transaction completion, effectively doubling the register cache refresh time.
195	I guess reliability comes at a price, but it's quite expensive this time.
196	
197	So, as not everyone might enjoy the slowdown, PEC can be disabled through
198	sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
199	to that file to enable PEC again.
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