1# How to Configure Phosphor-pid-control
2
3A system needs two groups of configurations: zones and sensors.
4
5## Json Configuration
6
7The json object should be a dictionary with two keys, `sensors` and `zones`.
8`sensors` is a list of the sensor dictionaries, whereas `zones` is a list of
9zones.
10
11### Sensors
12
13```
14"sensors" : [
15    {
16        "name": "fan1",
17        "type": "fan",
18        "readPath": "/xyz/openbmc_project/sensors/fan_tach/fan1",
19        "writePath": "/sys/devices/platform/ahb/ahb:apb/1e786000.pwm-tacho-controller/hwmon/**/pwm1",
20        "min": 0,
21        "max": 255
22    },
23    {
24        "name": "fan2",
25        "type": "fan",
26        "readPath": "/xyz/openbmc_project/sensors/fan_tach/fan2",
27        "writePath": "/sys/devices/platform/ahb/ahb:apb/1e786000.pwm-tacho-controller/hwmon/**/pwm2",
28        "min": 0,
29        "max": 255,
30        "timeout": 4,
31    },
32...
33```
34
35A sensor has a `name`, a `type`, a `readPath`, a `writePath`, a `minimum` value,
36a `maximum` value, and a `timeout`.
37
38The `name` is used to reference the sensor in the zone portion of the
39configuration.
40
41The `type` is the type of sensor it is. This influences how its value is
42treated. Supports values are: `fan`, `temp`, and `margin`.
43
44**TODO: Add further details on what the types mean.**
45
46The `readPath` is the path that tells the daemon how to read the value from this
47sensor. It is optional, allowing for write-only sensors. If the value is absent
48or `None` it'll be treated as a write-only sensor.
49
50If the `readPath` value contains: `/xyz/openbmc_project/extsensors/` it'll be
51treated as a sensor hosted by the daemon itself whose value is provided
52externally. The daemon will own the sensor and publish it to dbus. This is
53currently only supported for `temp` and `margin` sensor types.
54
55If the `readPath` value contains: `/xyz/openbmc_project/` (this is checked after
56external), then it's treated as a passive dbus sensor. A passive dbus sensor is
57one that listens for property updates to receive its value instead of actively
58reading the `Value` property.
59
60If the `readPath` value contains: `/sys/` this is treated as a directly read
61sysfs path. There are two supported paths:
62
63*   `/sys/class/hwmon/hwmon0/pwm1`
64*   `/sys/devices/platform/ahb/1e786000.pwm-tacho-controller/hwmon/<asterisk
65    asterisk>/pwm1`
66
67The `writePath` is the path to set the value for the sensor. This is only valid
68for a sensor of type `fan`. The path is optional. If can be empty or `None`. It
69then only supports two options.
70
71If the `writePath` value contains: `/sys/` this is treated as a directory
72written sysfs path. There are two support paths:
73
74*   `/sys/class/hwmon/hwmon0/pwm1`
75*   `/sys/devices/platform/ahb/1e786000.pwm-tacho-controller/hwmon/<asterisk
76    asterisk>/pwm1`
77
78If the `writePath` value contains: `/xyz/openbmc_project/sensors/fan_tach/fan{N}` it
79sets of a sensor object that writes over dbus to the
80`xyz.openbmc_project.Control.FanPwm` interface. The `writePath` should be the
81full object path.
82
83```
84busctl introspect xyz.openbmc_project.Hwmon-1644477290.Hwmon1 /xyz/openbmc_project/sensors/fan_tach/fan1 --no-pager
85NAME                                TYPE      SIGNATURE RESULT/VALUE                             FLAGS
86org.freedesktop.DBus.Introspectable interface -         -                                        -
87.Introspect                         method    -         s                                        -
88org.freedesktop.DBus.Peer           interface -         -                                        -
89.GetMachineId                       method    -         s                                        -
90.Ping                               method    -         -                                        -
91org.freedesktop.DBus.Properties     interface -         -                                        -
92.Get                                method    ss        v                                        -
93.GetAll                             method    s         a{sv}                                    -
94.Set                                method    ssv       -                                        -
95.PropertiesChanged                  signal    sa{sv}as  -                                        -
96xyz.openbmc_project.Control.FanPwm  interface -         -                                        -
97.Target                             property  t         255                                      emits-change writable
98xyz.openbmc_project.Sensor.Value    interface -         -                                        -
99.MaxValue                           property  x         0                                        emits-change writable
100.MinValue                           property  x         0                                        emits-change writable
101.Scale                              property  x         0                                        emits-change writable
102.Unit                               property  s         "xyz.openbmc_project.Sensor.Value.Uni... emits-change writable
103.Value                              property  x         2823                                     emits-change writable
104```
105
106The `minimum` and `maximum` values are optional. When `maximum` is non-zero it
107expects to write a percentage value converted to a value between the minimum and
108maximum.
109
110The `timeout` value is optional and controls the sensor failure behavior. If a
111sensor is a fan the default value is 2 seconds, otherwise it's 0. When a
112sensor's timeout is 0 it isn't checked against a read timeout failure case. If a
113sensor fails to be read within the timeout period, the zone goes into failsafe
114to handle the case where it doesn't know what to do -- as it doesn't have all
115its inputs.
116
117### Zones
118
119```
120"zones" : [
121        {
122            "id": 1,
123            "minThermalOutput": 3000.0,
124            "failsafePercent": 75.0,
125            "pids": [],
126...
127```
128
129Each zone has its own fields, and a list of PIDs.
130
131| field              | type      | meaning                                   |
132| ------------------ | --------- | ----------------------------------------- |
133| `id`               | `int64_t` | This is a unique identifier for the zone. |
134| `minThermalOutput` | `double`  | This is the minimum value that should be considered from the thermal outputs.  Commonly used as the minimum fan RPM.|
135| `failsafePercent`  | `double`  | If there is a fan PID, it will use this value if the zone goes into fail-safe as the output value written to the fan's sensors.|
136
137The `id` field here is used in the d-bus path to talk to the
138`xyz.openbmc_project.Control.Mode` interface.
139
140***TODO:*** Examine how the fan controller always treating its output as a
141percentage works for future cases.
142
143### PIDs
144
145There are a few PID types: `fan`, `temp`, `margin`, and `stepwise`.
146
147The `fan` PID is meant to drive fans. It's expecting to get the maximum RPM
148setpoint value from the owning zone and then drive the fans to that value.
149
150A `temp` PID is meant to drive the RPM setpoint given an absolute temperature
151value (higher value indicates a warmer temperature).
152
153A `margin` PID is meant to drive the RPM setpoint given a margin value (lower
154value indicates a warmer temperature).
155
156The setpoint output from the thermal controllers is called `RPMSetpoint()`
157However, it doesn't need to be an RPM value.
158
159***TODO:*** Rename this method and others to not say necessarily RPM.
160
161Some PID configurations have fields in common, but may be interpreted
162differently.
163
164#### PID Field
165
166If the PID `type` is not `stepwise` then the PID field is defined as follows:
167
168| field                | type     | meaning                                   |
169| -------------------- | -------- | ----------------------------------------- |
170| `samplePeriod`       | `double` | How frequently the value is sampled. 0.1 for fans, 1.0 for temperatures.|
171| `proportionalCoeff`  | `double` | The proportional coefficient.             |
172| `integralCoeff`      | `double` | The integral coefficient.                 |
173| `feedFwdOffsetCoeff` | `double` | The feed forward offset coefficient.      |
174| `feedFwdGainCoeff`   | `double` | The feed forward gain coefficient.        |
175| `integralLimit_min`  | `double` | The integral minimum clamp value.         |
176| `integralLimit_max`  | `double` | The integral maximum clamp value.         |
177| `outLim_min`         | `double` | The output minimum clamp value.           |
178| `outLim_max`         | `double` | The output maximum clamp value.           |
179| `slewNeg`            | `double` | Negative slew value to dampen output.     |
180| `slewPos`            | `double` | Positive slew value to accelerate output. |
181
182The units for the coefficients depend on the configuration of the PIDs.
183
184If the PID is a `margin` controller and its `setpoint` is in centigrade and
185output in RPM: proportionalCoeff is your p value in units: RPM/C and integral
186coefficient: RPM/C sec
187
188If the PID is a fan controller whose output is pwm: proportionalCoeff is %/RPM
189and integralCoeff is %/RPM sec.
190
191***NOTE:*** The sample periods are specified in the configuration as they are
192used in the PID computations, however, they are not truly configurable as they
193are used for the update periods for the fan and thermal sensors.
194
195#### type == "fan"
196
197```
198"name": "fan1-5",
199"type": "fan",
200"inputs": ["fan1", "fan5"],
201"setpoint": 90.0,
202"pid": {
203...
204}
205```
206
207The type `fan` builds a `FanController` PID.
208
209| field      | type              | meaning                                     |
210| ---------- | ----------------- | ------------------------------------------- |
211| `name`     | `string`          | The name of the PID. This is just for humans and logging.|
212| `type`     | `string`          | `fan`                                       |
213| `inputs`   | `list of strings` | The names of the sensor(s) that are used as input and output for the PID loop.|
214| `setpoint` | `double`          | Presently UNUSED                            |
215| `pid`      | `dictionary`      | A PID dictionary detailed above.            |
216
217#### type == "temp"
218
219***TODO:*** Add notes for temperature configuration.
220
221#### type == "margin"
222
223```
224"name": "fleetingpid0",
225"type": "margin",
226"inputs": ["fleeting0"],
227"setpoint": 10,
228"pid": {
229...
230}
231```
232
233The type `margin` builds a `ThermalController` PID.
234
235| field      | type              | meaning                                     |
236| ---------- | ----------------- | ------------------------------------------- |
237| `name`     | `string`          | The name of the PID. This is just for humans and logging.|
238| `type`     | `string`          | `margin`                                    |
239| `inputs`   | `list of strings` | The names of the sensor(s) that are used as input for the PID loop.|
240| `setpoint` | `double`          | The setpoint value for the thermal PID. The setpoint for the margin sensors.|
241| `pid`      | `dictionary`      | A PID dictionary detailed above.            |
242
243The output of a `margin` PID loop is that it sets the setpoint value for the
244zone. It does this by adding the value to a list of values. The value chosen by
245the fan PIDs (in this cascade configuration) is the maximum value.
246
247#### type == "stepwise"
248
249***TODO:*** Write up `stepwise` details.
250