1Kernel driver lm90
2==================
3
4Supported 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  * Analog Devices ADT7461A
36    Prefix: 'adt7461a'
37    Addresses scanned: I2C 0x4c and 0x4d
38    Datasheet: Publicly available at the ON Semiconductor website
39               http://www.onsemi.com/PowerSolutions/product.do?id=ADT7461A
40  * ON Semiconductor NCT1008
41    Prefix: 'nct1008'
42    Addresses scanned: I2C 0x4c and 0x4d
43    Datasheet: Publicly available at the ON Semiconductor website
44               http://www.onsemi.com/PowerSolutions/product.do?id=NCT1008
45  * Maxim MAX6646
46    Prefix: 'max6646'
47    Addresses scanned: I2C 0x4d
48    Datasheet: Publicly available at the Maxim website
49               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
50  * Maxim MAX6647
51    Prefix: 'max6646'
52    Addresses scanned: I2C 0x4e
53    Datasheet: Publicly available at the Maxim website
54               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
55  * Maxim MAX6648
56    Prefix: 'max6646'
57    Addresses scanned: I2C 0x4c
58    Datasheet: Publicly available at the Maxim website
59               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
60  * Maxim MAX6649
61    Prefix: 'max6646'
62    Addresses scanned: I2C 0x4c
63    Datasheet: Publicly available at the Maxim website
64               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
65  * Maxim MAX6657
66    Prefix: 'max6657'
67    Addresses scanned: I2C 0x4c
68    Datasheet: Publicly available at the Maxim website
69               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
70  * Maxim MAX6658
71    Prefix: 'max6657'
72    Addresses scanned: I2C 0x4c
73    Datasheet: Publicly available at the Maxim website
74               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
75  * Maxim MAX6659
76    Prefix: 'max6659'
77    Addresses scanned: I2C 0x4c, 0x4d, 0x4e
78    Datasheet: Publicly available at the Maxim website
79               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
80  * Maxim MAX6680
81    Prefix: 'max6680'
82    Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
83                           0x4c, 0x4d and 0x4e
84    Datasheet: Publicly available at the Maxim website
85               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
86  * Maxim MAX6681
87    Prefix: 'max6680'
88    Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
89                           0x4c, 0x4d and 0x4e
90    Datasheet: Publicly available at the Maxim website
91               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
92  * Maxim MAX6692
93    Prefix: 'max6646'
94    Addresses scanned: I2C 0x4c
95    Datasheet: Publicly available at the Maxim website
96               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
97  * Maxim MAX6695
98    Prefix: 'max6695'
99    Addresses scanned: I2C 0x18
100    Datasheet: Publicly available at the Maxim website
101               http://www.maxim-ic.com/datasheet/index.mvp/id/4199
102  * Maxim MAX6696
103    Prefix: 'max6695'
104    Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
105                           0x4c, 0x4d and 0x4e
106    Datasheet: Publicly available at the Maxim website
107               http://www.maxim-ic.com/datasheet/index.mvp/id/4199
108  * Winbond/Nuvoton W83L771W/G
109    Prefix: 'w83l771'
110    Addresses scanned: I2C 0x4c
111    Datasheet: No longer available
112  * Winbond/Nuvoton W83L771AWG/ASG
113    Prefix: 'w83l771'
114    Addresses scanned: I2C 0x4c
115    Datasheet: Not publicly available, can be requested from Nuvoton
116  * Philips/NXP SA56004X
117    Prefix: 'sa56004'
118    Addresses scanned: I2C 0x48 through 0x4F
119    Datasheet: Publicly available at NXP website
120               http://ics.nxp.com/products/interface/datasheet/sa56004x.pdf
121  * GMT G781
122    Prefix: 'g781'
123    Addresses scanned: I2C 0x4c, 0x4d
124    Datasheet: Not publicly available from GMT
125  * Texas Instruments TMP451
126    Prefix: 'tmp451'
127    Addresses scanned: I2C 0x4c
128    Datasheet: Publicly available at TI website
129               http://www.ti.com/litv/pdf/sbos686
130
131
132Author: Jean Delvare <jdelvare@suse.de>
133
134
135Description
136-----------
137
138The LM90 is a digital temperature sensor. It senses its own temperature as
139well as the temperature of up to one external diode. It is compatible
140with many other devices, many of which are supported by this driver.
141
142Note that there is no easy way to differentiate between the MAX6657,
143MAX6658 and MAX6659 variants. The extra features of the MAX6659 are only
144supported by this driver if the chip is located at address 0x4d or 0x4e,
145or if the chip type is explicitly selected as max6659.
146The MAX6680 and MAX6681 only differ in their pinout, therefore they obviously
147can't (and don't need to) be distinguished.
148
149The specificity of this family of chipsets over the ADM1021/LM84
150family is that it features critical limits with hysteresis, and an
151increased resolution of the remote temperature measurement.
152
153The different chipsets of the family are not strictly identical, although
154very similar. For reference, here comes a non-exhaustive list of specific
155features:
156
157LM90:
158  * Filter and alert configuration register at 0xBF.
159  * ALERT is triggered by temperatures over critical limits.
160
161LM86 and LM89:
162  * Same as LM90
163  * Better external channel accuracy
164
165LM99:
166  * Same as LM89
167  * External temperature shifted by 16 degrees down
168
169ADM1032:
170  * Consecutive alert register at 0x22.
171  * Conversion averaging.
172  * Up to 64 conversions/s.
173  * ALERT is triggered by open remote sensor.
174  * SMBus PEC support for Write Byte and Receive Byte transactions.
175
176ADT7461, ADT7461A, NCT1008:
177  * Extended temperature range (breaks compatibility)
178  * Lower resolution for remote temperature
179
180MAX6657 and MAX6658:
181  * Better local resolution
182  * Remote sensor type selection
183
184MAX6659:
185  * Better local resolution
186  * Selectable address
187  * Second critical temperature limit
188  * Remote sensor type selection
189
190MAX6680 and MAX6681:
191  * Selectable address
192  * Remote sensor type selection
193
194MAX6695 and MAX6696:
195  * Better local resolution
196  * Selectable address (max6696)
197  * Second critical temperature limit
198  * Two remote sensors
199
200W83L771W/G
201  * The G variant is lead-free, otherwise similar to the W.
202  * Filter and alert configuration register at 0xBF
203  * Moving average (depending on conversion rate)
204
205W83L771AWG/ASG
206  * Successor of the W83L771W/G, same features.
207  * The AWG and ASG variants only differ in package format.
208  * Diode ideality factor configuration (remote sensor) at 0xE3
209
210SA56004X:
211  * Better local resolution
212
213All temperature values are given in degrees Celsius. Resolution
214is 1.0 degree for the local temperature, 0.125 degree for the remote
215temperature, except for the MAX6657, MAX6658 and MAX6659 which have a
216resolution of 0.125 degree for both temperatures.
217
218Each sensor has its own high and low limits, plus a critical limit.
219Additionally, there is a relative hysteresis value common to both critical
220values. To make life easier to user-space applications, two absolute values
221are exported, one for each channel, but these values are of course linked.
222Only the local hysteresis can be set from user-space, and the same delta
223applies to the remote hysteresis.
224
225The lm90 driver will not update its values more frequently than configured with
226the update_interval attribute; reading them more often will do no harm, but will
227return 'old' values.
228
229SMBus Alert Support
230-------------------
231
232This driver has basic support for SMBus alert. When an alert is received,
233the status register is read and the faulty temperature channel is logged.
234
235The Analog Devices chips (ADM1032, ADT7461 and ADT7461A) and ON
236Semiconductor chips (NCT1008) do not implement the SMBus alert protocol
237properly so additional care is needed: the ALERT output is disabled when
238an alert is received, and is re-enabled only when the alarm is gone.
239Otherwise the chip would block alerts from other chips in the bus as long
240as the alarm is active.
241
242PEC Support
243-----------
244
245The ADM1032 is the only chip of the family which supports PEC. It does
246not support PEC on all transactions though, so some care must be taken.
247
248When reading a register value, the PEC byte is computed and sent by the
249ADM1032 chip. However, in the case of a combined transaction (SMBus Read
250Byte), the ADM1032 computes the CRC value over only the second half of
251the message rather than its entirety, because it thinks the first half
252of the message belongs to a different transaction. As a result, the CRC
253value differs from what the SMBus master expects, and all reads fail.
254
255For this reason, the lm90 driver will enable PEC for the ADM1032 only if
256the bus supports the SMBus Send Byte and Receive Byte transaction types.
257These transactions will be used to read register values, instead of
258SMBus Read Byte, and PEC will work properly.
259
260Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
261Instead, it will try to write the PEC value to the register (because the
262SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
263without PEC), which is not what we want. Thus, PEC is explicitly disabled
264on SMBus Send Byte transactions in the lm90 driver.
265
266PEC on byte data transactions represents a significant increase in bandwidth
267usage (+33% for writes, +25% for reads) in normal conditions. With the need
268to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
269two transactions will typically mean twice as much delay waiting for
270transaction completion, effectively doubling the register cache refresh time.
271I guess reliability comes at a price, but it's quite expensive this time.
272
273So, as not everyone might enjoy the slowdown, PEC can be disabled through
274sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
275to that file to enable PEC again.
276