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| xobs | mithro: it depends on the latency of gpio outputs, and how they're wired up. | 00:41 |
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| xobs | But potentially, yes. | 00:41 |
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| mithro | xobs: I have no idea what the difference between M0 / M4 is except that M4 has more "grunt" :-P | 02:31 |
| xobs | mithro: big difference is M0 is dumber and therefore more predictable in terms of cycle-counting. | 02:42 |
| mithro | Yeah -- the M4 pipeline could mean you can't turn around the IO fast enough? | 02:58 |
| xobs | Could be, or it could be that there's a synchronizer in front of the GPIO block. Grainuum takes advantage of the fact that on lots of M0+ chips, the GPIO is hooked up to the single-cycle port on the M0, so you get immediate, guaranteed latency. | 02:59 |
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| MadHacker | Grainuum is 12Mbit USB, not 1.5Mbit, yeah? | 08:12 |
| xobs | It's 1.5 MB LS. | 08:14 |
| MadHacker | Ah right. | 08:15 |
| MadHacker | Sorry, was confused on that point. The speed requirement seemed relatively high for 1.5, but I guess there's a lot going on there. | 08:15 |
| xobs | FS may be possible in 80 MHz, especially with an M4, but then you start having to do things with the framing. LS only has 8-byte packets, for example, so you don't have to oversample. | 08:16 |
| MadHacker | Yep. | 08:16 |
| MadHacker | I wonder if there's scope to abuse an SPI peripheral for it? Like we do for the WS2812 signalling? | 08:16 |
| MadHacker | Would take some of the literal bit-banging work away, but replace it by some extra shifts. | 08:17 |
| MadHacker | + would remove some of the timing predictability demands. | 08:17 |
| xobs | Interesting approach. Definitely doable for the Tx side. Lining up the Rx side could be challenging, though. | 08:20 |
| MadHacker | Mm, mostly a matter of bit-manipulation to shift things into the right position in the frame, I guess. | 08:21 |
| MadHacker | Did M0/M4 both drop the old single-cycle barrel shift ARM1 had? | 08:21 |
| xobs | Yeah, that's not in Thumb2. | 08:24 |
| MadHacker | Shame. I know why it wasn't good from an implementation point of view in silicon, but from a programmer's perspective that thing was great. | 08:25 |
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