Thursday, 2018-11-22

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mithrotannewt: evening01:18
mithrotannewt: I'm currently struggling with a good way to store the buffers01:18
tannewtmithro what buffers?01:21
mithrotannewt: endpoint buffers01:22
tannewtits usually dma or direct ram access01:22
tannewtso you just tell the peripheral where it is01:23
cr1901_modernmisoc/litex systems don't have a DMA controller I don't think (wouldn't be that difficult to add one I imagine)01:23
mithrotannewt: Sure, I'm just trying to figure out the best way to store the buffers in the ram....01:24
tannewtwhat are your options?01:25
mithrotannewt: Pretty much anything :-P01:27
tannewtI'd leave it up to the code, not the peripheral01:27
tannewtits something tinyusb already manages01:28
mithrotannewt: Well, having a one 32bit pointer for each endpoint is very expensive01:28
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tannewtah, so you want an offset?01:29
tannewtsamd actually stores them in ram in "sram registers"01:29
tannewtand the peripheral has one pointer to that01:30
mithrotannewt: So, I could have it so that as DATA OUT transfers happen, it just fills up a slot in buffers and each EP has a value which tells you which slot to look in to find the data...01:31
mithroOr I could just have each EP have a single buffer01:32
tannewtI think its good to have the location configurable because you save another copy to put it into something bigger01:34
tannewtits common for mass storage for the buffer to be longer than a single data transaction01:35
mithrohigh speed devices allow a packet size of 8, 16, 32 or 64 bytes01:35
tannewtbut it may chain more than one01:36
tannewtall the msc data transfers will be at least 512 bytes01:38
tannewtso if you force a specific 64 byte buffer you'll incur a copy to the larger buffer later01:38
xobsOften they're just fifos.01:39
xobsSo no need for dma.01:39
mithroxobs: That would be another option01:40
mithroI'm also trying to figure out if I should use separate buffer space for in and out endpoints or use a combined buffer space...01:45
xobsUsually I've seen it separated.01:47
cr1901_modernmithro: For litesdcard, when I last experimented, I ended up using a combined _double buffer_ space (buffer0-in, buffer1-in, buffer0-out, buffer1-out). Unfortunately I don't remember the rationale for this01:48
cr1901_modernin and out were separated by an offset, but they were both part of the same contiguous dual port memory chunk01:49
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xobsOkay, on an ICE40, what would cause the VCCPLL line to draw so much current?05:15
xobsI don't have exact numbers yet, but I have VCCPLL on its own regulator, and that regulator gets warm as long as the FPGA is out of reset.  This is regardless of whether the bitstream uses a PLL at all.05:15
xobsBut I know if I spray cold at it, the VCCPLL regulator defrosts very quickly.  And the other regulators not so much.05:16
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tannewtxobs: do you know of an svd to c converter we could run during a build process?06:50
xobstannewt: Just the svdconv.exe that cmsis generates.06:52
tannewtis it cross platform?06:54
xobsNot that I can see right now.  Which makes it rather useless.06:54
tannewtya, I agree06:54
tannewtI was thinking svd + converter would be a good foundation for cross-mcu libraries06:55
xobssvd is easy enough to parse in Rust, mostly because there's a crate for it already.  I started writing a utility to generate documentation, but I'm sure it could easily be modified to generate C or H files.06:58
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tannewtwill have to keep that in mind07:01
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froztbytemithro: heeeeeey you're doing a ccc talk23:31
froztbyteI'll be there :)23:31
froztbyte(and hopefully timing lines up to meet y'all)23:32

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