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DIOT Monitoring Module
DIOT Monitoring Module
Commit 2524efd8 authored by Christos Gentsos's avatar Christos Gentsos
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Doc: document the LINEAR16 format (implemented for VOUT in 00dc1498)

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doc/source/firmware.rst
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......@@ -63,13 +63,14 @@ The full list of PMBus and extended commands implemented by the
MoniMod can be found in :numref:`Tables %s <pmbus_cmds>` and
:numref:`%s <ext_cmds>`.
All physical quantities are expressed in the 16-bit PMBus Linear data
format (:numref:`linear_fmt`), instead of the Direct format PMBus also
supports, (which is somewhat more complex). An 11-bit mantissa (Y) and
a 5-bit exponent (N), expressed in 2's complement, form a
floating-point number X according to :math:`X = Y \cdot 2^N`.
All physical quantities (except output voltage, which is discussed
below) are expressed in the 16-bit PMBus Linear data format (LINEAR11,
:numref:`Linear`), instead of the (somewhat more complex) Direct
format PMBus also supports. An 11-bit mantissa (Y) and a 5-bit
exponent (N), expressed in 2's complement, form a floating-point
number X according to :math:`X = Y \cdot 2^N`.
.. _linear_fmt:
.. _Linear:
.. figure:: figures/latex/linear.png
:align: center
......@@ -77,6 +78,17 @@ floating-point number X according to :math:`X = Y \cdot 2^N`.
The PMBus Linear data format
The output voltages use a different, 21-bit format, called LINEAR16
(in contrast to the 16-bit LINEAR11, the names are derived from the
mantissa width). This format comprises a 5-bit 2's complement
exponent, reported by the 5 MSBs of the VOUT_MODE_ command; and a
16-bit unsigned mantissa, reported by READ_VOUT_. Many COTS PSUs use
LINEAR11 for everything, and this behavior is also possible using a
compile-time switch. In the MoniMod, the exponential factor for the
LINEAR16 format is fixed to -10, so the voltages reported can be
obtained with :math:`X = Y \cdot 2^-10`, where Y is the 16-bit value
returned by READ_VOUT_.
.. _pmbus_cmds:
.. table:: PMBus commands implemented by the MoniMod
......@@ -88,6 +100,8 @@ floating-point number X according to :math:`X = Y \cdot 2^N`.
+--------------+--------------------+------------------------+-------------+----------------------+
| 1A | QUERY | Block w / r proc. call | 1 | query cmd props |
+--------------+--------------------+------------------------+-------------+----------------------+
| 20 | VOUT_MODE | Byte read | 1 | read voltage format |
+--------------+--------------------+------------------------+-------------+----------------------+
| 3A | FAN_CONFIG_1_2 | Byte write / read | 1 | config fans 1&2 |
+--------------+--------------------+------------------------+-------------+----------------------+
| 3B | FAN_COMMAND_1 | Word write / read | 2 | set fan 1 speed |
......@@ -189,6 +203,24 @@ The QUERY command takes a command code as an argument and replies with
information on the command: whether it is supported, if read or write
is supported, and what data format it works with.
.. _VOUT_MODE:
VOUT_MODE
~~~~~~~~~
| Command code: **20**
| Transaction type: **Byte read**
| Data length: **1**
The VOUT_MODE command reports the format the device uses for measured
voltage related data. The 3 MSBs indicate whether that's Linear_
(0b000), VID (0b001) or Direct (0b010), and in the Monimod's case it's
always 0b000 for Linear format. The 5 MSBs return either 0x16, for
LINEAR16 format used (fully PMBus-compliant operation, fixed
:math:`2^-10` exponential); or 0x00, for LINEAR11 format used (common
for COTS PSUs). See Linear_ for more details on the specifics of these
formats.
FAN_CONFIG_n_m
~~~~~~~~~~~~~~
......@@ -242,6 +274,8 @@ The FAN_COMMAND_n commands set the desired speed of the attached
fans. The value set is either in RPMs (when the fan is configured to
be controlled like that) or duty cycle, in the range 0--1000.
.. _READ_VOUT:
READ_VOUT
~~~~~~~~~
......
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