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<sorear>
sweet
<sorear>
i was thinking you'd need to do more RE to get DDR3 working, but "I have a board with SDRAM" works too
<sorear>
what's the transfer rate on the SDRAM?
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<daveshah>
Everything is running at 25MHz because there are no PLLs
<daveshah>
It's only a 16 bit SDRAM so if the caches aren't pulling their weight it will be a bottleneck
<daveshah>
My masters project at uni will be getting things to the point we can have DDR3, as much general timing constraints work in nextpnr as ECP5 specific stuff
<daveshah>
tbh, I'm surprised how usable BusyBox and Linux is at 25MHz
<sorear>
how big is the sdram?
<daveshah>
Reminds me of DSLinux back in the day (67MHz ARM9)
<daveshah>
32MB of SDRAM
<daveshah>
20MB usable after kernel and initrd
<sorear>
does the board have any other storage (SD cards, etc)?
<sorear>
wait, there are ice40 boards with sdram, how has this not been done before
<daveshah>
There's an SD slot and SPI flash, but I'm not using either yet
<qu1j0t3>
daveshah: At which the retrocomputing community sighs, "25MHz? LUXURY"
* qu1j0t3
cues the Four Yorkshiremen
<daveshah>
I don't think anyone really managed to get a processor, MMU and SDRAM controller onto an ice40
<daveshah>
ice40 doesn't have distributed ram which these things tend to assume either
<daveshah>
MMU-less linux on ice40 is certainly doable, just no one has bothered
<sorear>
i've done some preliminary estimates for the smallest possible MMU that can be tacked on to picorv32, haven't really looked at SDRAM at all
* ZipCPU
tried to place a cache on an iCE40. Was successful, with *EXCEPTIONALLY SMALL* cache.
<daveshah>
If you don't care about performance, I don't think an SDRAM controller should be too big
<cr1901_modern>
If you _really_ don't care about performance, you can do one of those ancient async DRAM controllers in two or three greenpaks, or one greenpak and some 7400 series logic :P
<sorear>
I'm now thinking about the old Margulis CAM and wondering what the minimum amount of logic you need to do something clever with a sdram is