<danderson>
Mellow greetings. I'm starting out in FPGAs with an ECP5 board, and the demo blinky program I used to test my toolchain disables a bunch of things: `synth_ecp5 -nomux -nodram -noccu2 -json blinky.json`.
<danderson>
Where might I go to learn about what those mean, and why I'd want them turned off? At a quick glance, they seem to be giving yosys less freedom to do efficient synthesis, but I don't quite see why.
<danderson>
I should rephrase: the yosys manual covers the "what" of those options, what I'm hoping for is the "why" :)
<danderson>
Looking at yosys's output, at least -noccu2 influences the synthesis quite a bit. With ccu2, the synth is 12 CCU2C and 31 TRELLIS_FF blocks. Without, it's 31 LUT4 and 31 TRELLIS_FF.
<sensille>
danderson: who told you to do so? i don't use those options with my ecp5
<danderson>
That's the project I'm using to do basic toolchain verification, i.e. "do I have the right bits installed"
<danderson>
now I'm dissecting its makefile to understand the build process, and those synthesis options are what it uses.
<danderson>
Sounds like this may be a case of "remove those switches until you understand why you'd want them" :)
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<sensille>
yeah
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<danderson>
Ah, this blinky project was adapted from another blinky that dates to the early days of ECP5 support. So, I'm suspecting that those disabled things used to not work.
<sensille>
haha, from the early days of blinky
<danderson>
The heady days where leds only blunk after careful coaxing
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