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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. | 09:38 |
|---|---|---|
| whitequark | pepijndevos: doesn't | 09:38 |
| pepijndevos | ok | 09:38 |
| whitequark | also i feel like if yosys dropped some combinatorial ieee754 ops into your design you'd suddenly start caring about speed and area | 09:39 |
| pepijndevos | haha maybe | 09:39 |
| whitequark | right now floats are secretly strings | 09:39 |
| whitequark | which... is a pretty awful representation if you ask me | 09:40 |
| pepijndevos | w-what? | 09:40 |
| whitequark | floats in yosys are just strings in the decimal notation | 09:40 |
| whitequark | like a float RTLIL::Const is a byte vector containing ASCII containing the float in decimal | 09:41 |
| pepijndevos | So... what happens if you synth a design with floats? | 09:41 |
| whitequark | no idea | 09:41 |
| whitequark | i'm sure it breaks but i don't know how exactly | 09:41 |
| pepijndevos | lol ok | 09:41 |
| whitequark | 1364.1 is clear about floats not being synthesizable tho | 09:41 |
| pepijndevos | 100% sure quartus does it though. Back when I assisted FPGA labs in uni, I've seen some unfortunate souls try. | 09:42 |
| whitequark | huh | 09:43 |
| whitequark | i wonder if it's quartus itself or just synplify | 09:43 |
| pepijndevos | Combinatorial float FFT did not fit on the FPGA though | 09:43 |
| pepijndevos | Maybe I'll mess around and see if the Gowin or Latice tools can do it. Gowin usus Synplify IIRC | 09:45 |
| pepijndevos | Gowin using Symplify pro: Synthesis of real vin_val is not supported | 10:12 |
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| pepijndevos | Seems quartus support is also rather limited actually | 10:16 |
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| daveshah | It is probably mostly for the Stratixes with hard float DSPs these days | 10:20 |
| Lofty | Actually the Cyclone 10GX supports some measure of floating point arithmetic | 10:52 |
| Lofty | But the hardware *can* do it | 10:53 |
| daveshah | Oh interesting I thought it was only the Stratix 10 | 10:54 |
| daveshah | And their newer agilex or whatever it's called | 10:54 |
| Lofty | It's probably further enhanced on those architectures, but it's still got support on C10GX | 10:56 |
| daveshah | Mmm | 10:57 |
| daveshah | Xilinx are doing it too with Versal | 10:57 |
| 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 | 10:58 |
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| thardin | there we go, thought I forgot a channel | 20:11 |
| thardin | got my little lock-in amplifier working. with filters tunable by potentiometer | 20:12 |
| thardin | realizing I can do multiplication as bits arrive from the ADC was a life-saver | 20:18 |
| emeb | Oooo - lockin amps are fun. Yours is an all digital version? | 20:24 |
| thardin | except for the ADCs and DACs yes | 20:31 |
| thardin | it's very bare bones at the moment | 20:31 |
| thardin | an octopus of pmods coming off the icestick, with a hand-soldered board for the pots for good measure | 20:32 |
| emeb | Is it dual-phase? | 20:35 |
| thardin | not yet | 20:35 |
| thardin | might need a larger device for that | 20:35 |
| thardin | in fact I haven't added adjustable phase to the mixer yet | 20:36 |
| emeb | Yeah - the HX1k on icestick is a bit small. | 20:36 |
| thardin | I was looking at HX8K board a few weeks ago | 20:36 |
| emeb | The DSP cores in UP5k might be useful for that. | 20:37 |
| thardin | I'm only doing addition and look-ups at the moment | 20:37 |
| thardin | but if I were to bump up the speed into the tens of MHz then being able to multiply faster would be useful | 20:38 |
| emeb | Interesting. How do you do the mixing operation w/o multiplication? | 20:38 |
| thardin | it does serial multiplication | 20:38 |
| emeb | aha | 20:38 |
| thardin | as in, it remembers the last LO sample and for each non-zero ADC bit it adds it shifted to an accumulator | 20:38 |
| emeb | yep. longhand | 20:38 |
| emeb | so your sample rate is << clock rate | 20:39 |
| thardin | yeah it's 1/32 | 20:39 |
| thardin | I only need 100 kHz bandwidth for now | 20:40 |
| emeb | how do you generate sinusoids? LUT? | 20:40 |
| thardin | yeah | 20:40 |
| thardin | plus symmetry | 20:40 |
| emeb | what's the phase resolution? | 20:40 |
| thardin | so it stores 0-90° | 20:40 |
| thardin | uh.. the table is 4096 entries so | 20:40 |
| thardin | let's see | 20:40 |
| emeb | 2pi/16k | 20:40 |
| thardin | 0.02° | 20:40 |
| thardin | 0.4 mrad | 20:41 |
| emeb | not bad | 20:41 |
| thardin | should be more than enough | 20:41 |
| emeb | Yeah. | 20:42 |
| thardin | plan is to squeeze the design into a eurorack module | 20:42 |
| emeb | heh | 20:42 |
| thardin | they're not just for musicians! | 20:42 |
| * emeb does DSP for eurorack | 20:43 | |
| thardin | cool | 20:43 |
| emeb | hard to imagine doing "real science" with that stuff. Presumably you just use the rack, supplies and physical dimensions for some custom equipment? | 20:44 |
| thardin | yeah there's modules aimed at academia | 20:45 |
| emeb | Interesting. Got a link so such stuff? | 20:46 |
| emeb | link to? | 20:46 |
| thardin | nope, but if you search around for laser stuff you'll probably find some | 20:46 |
| thardin | they come with a hefty price tag | 20:46 |
| emeb | I'm sure | 20:46 |
| 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. | 20:47 |
| thardin | pew pew | 20:47 |
| thardin | a laser is just a radio running at much higher frequency | 20:47 |
| emeb | true dat | 20:48 |
| thardin | you have non-linear optics that behave much like RF mixers | 20:48 |
| emeb | indeed - hence green laser pointers | 20:48 |
| thardin | so you can beam two lasers into it and get the difference in frequency out as RF | 20:49 |
| emeb | how does one get that difference freq into a circuit though? Stick an antenna on the crystal? | 20:50 |
| thardin | they probably have some kind of antenna there yes | 20:50 |
| thardin | a transition of some sort | 20:50 |
| thardin | you can go the other way with pockels cells and similar devices | 20:50 |
| thardin | modulate a laser with RF | 20:51 |
| thardin | you also have piezo devices that do aucusto-optical modulation | 20:51 |
| emeb | yep - that's what I've seen before. | 20:51 |
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| emeb | and of course simple AM of laser emitters by modulating supply voltages. | 20:52 |
| thardin | yes | 20:53 |
| emeb | worked on a microwave RF delay based on that long ago. 2GHz -> IR laser diode -> long coil of fiber optic -> detector. | 20:53 |
| thardin | nice | 20:53 |
| emeb | Hard to get a good RF match on a commercial IR laser diode. | 20:54 |
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