Added smooth power doc.

doc/ETHASH_SMOOTH_POWER.md

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+# TeamRedMiner Ethash Smooth Power
+
+
+## Overview
+
+In TRM, "smooth power" means carefully managing gpu activity to
+produce the smoothest possible power draw over time on a fine-grained
+level. The technique is used for all gpu types and on all algos in the
+ethash family (ethash, etchash, kawpow, firopow). The objective is to
+be as nice as possible to the whole power delivery system, from PSU to
+risers to GPU VRMs. The assumption is that if we make life easy for
+the voltage regulators we should be able to survive on a lower voltage
+than in previous TRM versions and other miners. The way we address the
+problem in TRM also has the nice side effect of slightly increasing
+hashrate on most gpus, normally in the 0.1-0.2% range.
+
+To illustrate what the above means in practice, please see the
+following scope captures of 5 secs of uninterrupted ethash mining with
+TRM 0.9.4.2, Phoenix 6.2c, lolminer 1.51a, and TRM 0.10.2, all on a
+Sapphire Pulse 580 at a ~31 MH/s tuning. All captures were performed
+using a Siglent SDS2104X Plus and a 300kHz CP6220 current probe.
+
+| TRM 0.9.4.2 |
+|:--:|
+| ![TRM 0.9.4.2](pics/smooth_trm0942_5secs.png) |
+
+
+| Phoenix 6.2c |
+|:--:|
+| ![Phoenix 6.2c](pics/smooth_phoenix62c_5secs.png) |
+
+
+| lolminer 1.51a |
+|:--:|
+| ![lolminer 1.51a](pics/smooth_lolminer151a_5secs.png) |
+
+
+| TRM 0.10.2 |
+|:--:|
+| ![TRM 0.10.2](pics/smooth_trm0102_5secs.png) |
+
+
+Clearly visible, all miners except TRM 0.10.2 suffer from repeated
+up/down spikes, i.e. deviations from the average power draw. Lolminer
+is exhibiting the worst behavior. Phoenix and TRM 0.9.4.2 behave
+similarly with Phoenix having slightly less pronounced spikes but
+occuring more frequently. The outlier is TRM 0.10.2 that has a smooth
+continuous draw without any spikes at all deviating from the average
+level.
+
+To verify that the new behavior in TRM 0.10.2 does indeed translate
+into more robust mining at lower voltages we tested running the same
+Sapphire Pulse 580 at 1138 MHz core, 2080 MHz mem, ref 30 for 30.9
+MH/s at a low core voltage of 793mV.
+
+| Miner          | Result                               |
+| -------------- | ------------------------------------ |
+| TRM 0.9.4.2    | Crashed immediately after dag build. |
+| Phoenix 6.2c   | Crashed after 10 secs of tuning.     |
+| lolminer 1.51a | Crashed immediately after dag build. |
+| TRM 0.10.2     | Ran for 2h without crashing.         |
+
+
+NOTE: the smooth power feature was released in v0.10.0, but in
+hindsight it needed additional polishing and fine-tuning, especially
+for Polaris and Vega gpus. We hope that the version released in
+v0.10.2 will address earlier issues.
+
+## GPU tuning and results
+
+This feature normally doesn't need tuning, but a few pointers are
+still interesting:
+
+- As you try to minimize voltages, **switch to a static --eth_config
+  for all gpus**. This will skip the tuning part and enter the best
+  continuous smooth power setup we can produce immediately after the
+  dag build.
+
+- Our Polaris tuning had a preference to increase intensity on certain
+  mem straps in 0.10.0 and 0.10.1. This could trip some rigs, and was
+  not intended. This is fixed in v0.10.2, but we still recommend using
+  a static --eth_config when trying to tune for a low voltage.
+
+- As always with advanced features, some gpus simply aren't reacting
+  the way theory dictates they should. If you can't seem to get a gpu
+  stable regardless of what you try, you can always test turning off
+  the smooth power feature. Using e.g. `--eth_smooth_power=1,1,0,0,1`
+  would turn it off for gpus 2 and 3 in the rig but keep it enabled
+  for gpus 0, 1, and 4. Passing `--eth_smooth_power=0` will turn off
+  the feature for all gpus in the rig.
+
+GPU-specific pointers:
+
+- Polaris: we've found that most Polaris gpus can be lowered 10-15mV,
+  all else being equal, in some cases more as well. Unfortunately,
+  there are always some bad silicon samples that will need a certain
+  amount of voltage for stability.
+
+- RX Vegas: same as for Polaris, many gpus can shave off additional
+  core voltage but still remain stable. If you've had issues remaining
+  stable on RX Vegas in general on later TRM versions, you should try
+  switching to v0.10.2 but keep the old tuning. If you still have
+  issues, try turning off smooth power.
+
+- VIIs: no expected change in voltage required, no need to retune.
+
+- Navi: our testing indicates that smooth power results in increased
+  stability on the vast majority of Navi gpus. For the remaining ones
+  that rather seems to be crashing more often, turning off smooth
+  power is a good test.