Save a division at runtime by pre-calculating the slope between each
pair of adjacent thermistortable values. Since we use the larger value
each time, save the slope between two values A and B in the table
with the B data. Therefore the slope is that between each value and
its predecessor in the list.
Store this new value in the third element of the now 3-integers-wide
array which makes up the table. Use fixed-point 6.10 format to store
the slope. This is almost too narrow for some slopes and maybe it
should be changed to 8.8 fixed-point. In practice this presents a
loss in accuracy, but it is still significantly better than the
previous fixed-sample-size table production method. In particular no
provision is made to handle values which scale over 65535, and it
seems we should at least warn about this if not simply fail before
letting the user go off compiling his code.
Add a new flag TEMPTABLE_FORMAT and define it as 1 to tell the code
that we are using this new and incompatible format. This lets us
tolerate old hand-crafted thermistor tables by keeping the slower
algorithm in case one is still used. New thermistor tables should be
defined with this new format and with the FORMAT define set accordingly.
With the default 25 samples this adds 100 bytes to the flash image for
the thermistortable storage for two different thermistors. But the
code is simplified and saves me 134 bytes in the bargain for a net
decrease in flash size of 34 bytes.
The Thermistortablefile.py routine prematurely drops the
fractional part of the temperature when computing the 14.2
temperature values to emit in the code. Keep this instead until
the last moment when we finally calculate the integer format we
will store.
Temperature tables are emitted by selecting arbitrary sample values
to be used for the linear lookup table. This is fine in the range
where the thermistor produces linear output, but it is markedly wrong
near the extremes where the thermister output begins to curve.
Introduce a new sample selector which chooses samples based on the "most
incorrect estimate" and improves from there to ensure we get a cleaner
approximation across the selected range.
Traumflug: this topic is tracked here:
https://github.com/Traumflug/Teacup_Firmware/pull/208
Previously they were evenly spaced across the temperature range,
now they're evenly distributed across the ADC range ... which
is not entirely the same.
This is related to issue #176.
This is, the parameter entry fields in the GUI, not in the
generated temperature table. Allowing floats is a tiny bit more
precise and also, more importantly, less confusing for the user.
--Traumflug
This is related to issue #176.
The Steinhart-Hart algorithm allows more precise thermistor
tables, but also requires more parameters, which aren't
available for all thermistors. Accordingly, add support for both,
the traditional logic using the beta parameter as well as the new
one.
This also adds thermistor-presets, so users can simply choose
from a pulldown-menu to set their thermistor.
Also, identical thermistors get merged into one table, saving
binary size.
Last not least, a few bugs in this area got fixed.
Usually, all these things go into separate commits, but they were
contributed all in one and separating them is a bit error-prone
for little gain.
This should address issue #130, #134 and #135.
Markus Hitter
Phil Hord
Phil Hord
jbernardis