for pulses, we currently use amplitude detection.
edge detection is better, because weak / low gain
signals will be more reliable. if audio is coming
in on/from a system that does automatic gain
adjustment, this once again is more robust too.
microphones and speakers (which people often use
with spkmodem if nothing else available) often
clamp amplitude, to an extent that this software
may not detect those pulses reliably that way.
so we detect slope edges instead. this causes
very little performance penalty (use of abs(),
that's about it)
however, edge detection is inherently vulnerable
to noise, so we will also detect amplitude. this
acts as an effective noise filter, while still
improving pulse detection.
Signed-off-by: Leah Rowe <leah@libreboot.org>
this check no longer applies (never triggers)
is_signal_valid already guarantees that the separator
tone is valid.
Signed-off-by: Leah Rowe <leah@libreboot.org>
bits are currently assembled even on invalid frames. this
patch fixes that - the bug is also in the GNU version.
this reduces the chance of noise/calibration from creating
corrupt character output during operation.
Signed-off-by: Leah Rowe <leah@libreboot.org>
enforce at least two tones. this mitigates the
chance of random noise being treated as a real
tone, and reduces the chance of broken
thresholds versus freq min/max e.g.
freq min 31, max 32 and threshold 31
Signed-off-by: Leah Rowe <leah@libreboot.org>
we weren't actually using what we calculated. this patch
fixes that, thus preventing random noise / microphone
clicks, random artifacts and such from being treated
as real frames (the purpose of is_valid_signal is
partly noise suppression).
Signed-off-by: Leah Rowe <leah@libreboot.org>
in handle audio, i do the number of samples
per frame, and one more. e.g. 241 instead of
240. this bug is in the original GNU version
too. this patch fixes it.
this means that the output could slowly go
out of sync with calculated timings. the
patch fixes that. in practise, the decoder
is not that sensitive, and the code would
adjust anyway (automatic timing adjustment),
but ideally we want to not *cause* such
issues even if we mitigate them.
Signed-off-by: Leah Rowe <leah@libreboot.org>
assert integer sizes, important in this program because
we make several implicit assumptions about word sizes,
and integers need to be of a certain size.
Signed-off-by: Leah Rowe <leah@libreboot.org>
collect_separator should be select_separator, to bring
it in line with select_low_tone
this just makes the code a bit easier to read
Signed-off-by: Leah Rowe <leah@libreboot.org>
the fir filter produces stable frequencies per frame,
but learning per sample (within a frame) means we
record the same value roughly 240 times.
here, we are syncing up at just the right moment
instead, and only at that moment, this increasing
both performance and reliability.
Signed-off-by: Leah Rowe <leah@libreboot.org>
oops!!!
another mistake during refactoring. right now it
doesn't increment before being checked, so learning
can go forever in an infinite loop
Signed-off-by: Leah Rowe <leah@libreboot.org>
i conflated two separate tests in a previous change.
the silence check was defeated by still checking f
alongside it, which would be set, thus satisfying
the condition, and proceeding, which defeats the
purpose of the silence check (ignore false signal
that is actually noise) - so in the original patch
that i wrote, the extra checks actually do nothing.
this patch fixes that, and makes the logic a bit
clearer.
Signed-off-by: Leah Rowe <leah@libreboot.org>
the tone detection currently only tracks data, not
the separator. track both instead, for improved
detection reliability.
e.g.
separator tone ≈ 9
data low tone ≈ 18
data high tone ≈ 24
two fir windows produce e.g.
freq data 9 sep 0
then 18, 9
then 24, 9
18, 9
so we take min(data, separator)
that gives 9,9,9,9
now we have the separator cluster
however, if both windows are active during transitions,
you can also capture the higher clusters, which would
allow freq_max to grow
so when you learn e.g.:
freq min = 9
freq max 24
then the learned threshold would be:
(9 + 24) / 2 = 16
and now you know how to separate the tones
fir already suppresses noise so the pulse should
be reliable. so freq/sep only go non-zero when an
actual tone exists
this should now result in being able to sync with
spkmodem encoders with no prior knowledge of the
correct tone frequences. we just use maths.
Signed-off-by: Leah Rowe <leah@libreboot.org>
since we have auto-detection now, we only need to know
that two signals exist, not that they are valid, since
the auto-detection now handles validation and fallback.
Signed-off-by: Leah Rowe <leah@libreboot.org>
a continuation of the previous patch. this waits for
currently one second, before defaulting to the hardcoded
value. otherwise, it tries to use whatever timing it
gets automatically.
this way, the program should now reconfigure its own
timing, without intervention by the user, if the timing
differs from sensible defaults.
this is because spkmodem is implementation-defined;
it's just however coreboot and/or GRUB happen to set
it up, and on the hardware in question.
Signed-off-by: Leah Rowe <leah@libreboot.org>
current logic is hardcoded, as in the original spkmodem-recv.
with this change, small differences are observed and averaged,
then the detection thresholds are adjusted accordingly.
the existing macros serve as a baseline, but real signals
differ. with this change, we therefore account for possible
drift in timings, which can change in real-time; the old
code could possibly get out of sync beccause of that, which
may have resulted in corrupt characters on the screen. this
change therefore should make the output a bit more stable.
the detection window is continually adjusted, so that the
output timings don't drift.
the tolerances are automatically adjusted based on base
timings (see new define in patch)
Signed-off-by: Leah Rowe <leah@libreboot.org>
instead of when it goes above, do it precisely on the
timeout. otherwise, if by sheer chance the signal
pauses and we reset the byte - sure, ok, but it's a
bit tight and we run the risk of advancing another
frame, depending on the timing.
this is a minor edge case, probably rarely ever
triggered in practise.
Signed-off-by: Leah Rowe <leah@libreboot.org>
