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<pepijndevos>
Yosys doesn't synthesize floats, or does it? I know it's bad, but for a thing where I don't really care about speed or area, it beats fiddling with fixed point.
<whitequark>
pepijndevos: doesn't
<pepijndevos>
ok
<whitequark>
also i feel like if yosys dropped some combinatorial ieee754 ops into your design you'd suddenly start caring about speed and area
<pepijndevos>
haha maybe
<whitequark>
right now floats are secretly strings
<whitequark>
which... is a pretty awful representation if you ask me
<pepijndevos>
w-what?
<whitequark>
floats in yosys are just strings in the decimal notation
<whitequark>
like a float RTLIL::Const is a byte vector containing ASCII containing the float in decimal
<pepijndevos>
So... what happens if you synth a design with floats?
<whitequark>
no idea
<whitequark>
i'm sure it breaks but i don't know how exactly
<pepijndevos>
lol ok
<whitequark>
1364.1 is clear about floats not being synthesizable tho
<pepijndevos>
100% sure quartus does it though. Back when I assisted FPGA labs in uni, I've seen some unfortunate souls try.
<whitequark>
huh
<whitequark>
i wonder if it's quartus itself or just synplify
<pepijndevos>
Combinatorial float FFT did not fit on the FPGA though
<pepijndevos>
Maybe I'll mess around and see if the Gowin or Latice tools can do it. Gowin usus Synplify IIRC
<pepijndevos>
Gowin using Symplify pro: Synthesis of real vin_val is not supported
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<pepijndevos>
Seems quartus support is also rather limited actually
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<daveshah>
It is probably mostly for the Stratixes with hard float DSPs these days
<Lofty>
Actually the Cyclone 10GX supports some measure of floating point arithmetic
<Lofty>
But the hardware *can* do it
<daveshah>
Oh interesting I thought it was only the Stratix 10
<daveshah>
And their newer agilex or whatever it's called
<Lofty>
It's probably further enhanced on those architectures, but it's still got support on C10GX
<daveshah>
Mmm
<daveshah>
Xilinx are doing it too with Versal
<Lofty>
The S10 (and presumably Agilex) both changed the ALM a bit, so I'm gonna have to investigate that. If anybody decides to care/pay me
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<thardin>
there we go, thought I forgot a channel
<thardin>
got my little lock-in amplifier working. with filters tunable by potentiometer
<thardin>
realizing I can do multiplication as bits arrive from the ADC was a life-saver
<emeb>
Oooo - lockin amps are fun. Yours is an all digital version?
<thardin>
except for the ADCs and DACs yes
<thardin>
it's very bare bones at the moment
<thardin>
an octopus of pmods coming off the icestick, with a hand-soldered board for the pots for good measure
<emeb>
Is it dual-phase?
<thardin>
not yet
<thardin>
might need a larger device for that
<thardin>
in fact I haven't added adjustable phase to the mixer yet
<emeb>
Yeah - the HX1k on icestick is a bit small.
<thardin>
I was looking at HX8K board a few weeks ago
<emeb>
The DSP cores in UP5k might be useful for that.
<thardin>
I'm only doing addition and look-ups at the moment
<thardin>
but if I were to bump up the speed into the tens of MHz then being able to multiply faster would be useful
<emeb>
Interesting. How do you do the mixing operation w/o multiplication?
<thardin>
it does serial multiplication
<emeb>
aha
<thardin>
as in, it remembers the last LO sample and for each non-zero ADC bit it adds it shifted to an accumulator
<emeb>
yep. longhand
<emeb>
so your sample rate is << clock rate
<thardin>
yeah it's 1/32
<thardin>
I only need 100 kHz bandwidth for now
<emeb>
how do you generate sinusoids? LUT?
<thardin>
yeah
<thardin>
plus symmetry
<emeb>
what's the phase resolution?
<thardin>
so it stores 0-90°
<thardin>
uh.. the table is 4096 entries so
<thardin>
let's see
<emeb>
2pi/16k
<thardin>
0.02°
<thardin>
0.4 mrad
<emeb>
not bad
<thardin>
should be more than enough
<emeb>
Yeah.
<thardin>
plan is to squeeze the design into a eurorack module
<emeb>
heh
<thardin>
they're not just for musicians!
* emeb
does DSP for eurorack
<thardin>
cool
<emeb>
hard to imagine doing "real science" with that stuff. Presumably you just use the rack, supplies and physical dimensions for some custom equipment?
<thardin>
yeah there's modules aimed at academia
<emeb>
Interesting. Got a link so such stuff?
<emeb>
link to?
<thardin>
nope, but if you search around for laser stuff you'll probably find some
<thardin>
they come with a hefty price tag
<emeb>
I'm sure
<emeb>
I know some of our customers use the synth modules for controlling galvos in laser shows, but that's about as close as I come to laser stuff.
<thardin>
pew pew
<thardin>
a laser is just a radio running at much higher frequency
<emeb>
true dat
<thardin>
you have non-linear optics that behave much like RF mixers
<emeb>
indeed - hence green laser pointers
<thardin>
so you can beam two lasers into it and get the difference in frequency out as RF
<emeb>
how does one get that difference freq into a circuit though? Stick an antenna on the crystal?
<thardin>
they probably have some kind of antenna there yes
<thardin>
a transition of some sort
<thardin>
you can go the other way with pockels cells and similar devices
<thardin>
modulate a laser with RF
<thardin>
you also have piezo devices that do aucusto-optical modulation
<emeb>
yep - that's what I've seen before.
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<emeb>
and of course simple AM of laser emitters by modulating supply voltages.
<thardin>
yes
<emeb>
worked on a microwave RF delay based on that long ago. 2GHz -> IR laser diode -> long coil of fiber optic -> detector.
<thardin>
nice
<emeb>
Hard to get a good RF match on a commercial IR laser diode.
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