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| sensille | zyp: how do you mean? cpu time in the communcation functions? | 04:34 |
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| zyp | sensille, yes | 08:22 |
| sensille | no idea, can't be much. just building/parsing a smallish udp packet | 08:23 |
| sensille | one per millisecond | 08:23 |
| zyp | I looked at both litehm2, litex-cnc and colorcnc (I think it was called), but neither was entirely what I wanted, so I started my own approach based on a custom ethercat-like protocol where a single packet passes through a chain of devices that rewrites it | 08:26 |
| zyp | because part of what I want to do is distribute IO across multiple boards: https://bin.jvnv.net/file/sOo86.mp4 | 08:28 |
| sensille | my approach was to built on the 20+ years maturity of the existing code, host+fpga side | 08:29 |
| zyp | yeah, I get that, it just doesn't suit what I want to do well :) | 08:31 |
| zyp | but I'm curious how the communication performance I'm getting compares to other ethernet-based devices | 08:32 |
| sensille | i found ethercat quite appealing, but was repelled by the patents on it | 08:32 |
| zyp | indeed, that's why I'm not attempting to implement actual ethercat | 08:32 |
| sensille | but nice work if you can already pass packets through both ports | 08:32 |
| zyp | my main goal is to make something to drive this thing: https://bin.jvnv.net/file/2pVce.jpg | 08:35 |
| zyp | by making a custom fpga-based controller card that hooks up to the original power electronics | 08:35 |
| zyp | so I'm making custom hardware, which means I want the flexibility to handle arbitrary ADCs and similar in gateware, so the hm2 approach seems a little constraining | 08:39 |
| zyp | wheras colorcnc/litex-cnc is apparently based on etherbone, which seems like it'll be a performance bottleneck if you've got many signals | 08:40 |
| _florent_ | zyp: interesting project! Feel free to share advance/progress here, I'm also interested by this :) | 09:38 |
| _florent_ | zyp: Etherbone is indeed probably not the best for your application, it's mostly intended for MMAP. | 09:39 |
| zyp | I've designed it so the devices contains metadata about what signals it got, which types they have and at what offset in the data frame they're located, so I can simply just declare a few signals like this: https://paste.jvnv.net/view/Gy09s and have them show up in linuxcnc: https://bin.jvnv.net/file/WYbrd.png | 09:40 |
| tpb | Title: JVnV Pastebin – View paste – Untitled (at paste.jvnv.net) | 09:40 |
| _florent_ | zyp: If you want similar latency than Ethercat, you'll indeed have to have a non-standard MAC. | 09:41 |
| _florent_ | zyp: Another possibility if you want to reuse LiteEth could be to have a custom protocol over UDP, ex here with just raw streaming: | 09:42 |
| zyp | yeah, right now I'm using the standard mac, with a custom L3 handler, so each device adds latency corresponding to the preamble and L2 header, plus CDC | 09:42 |
| _florent_ | https://twitter.com/enjoy_digital/status/1486381439469957120 | 09:42 |
| zyp | so probably on the order of a hundred ns per device | 09:42 |
| zyp | but that drowns in the host side latency, linuxcnc says my data exchange function takes 40-50 us to execute | 09:43 |
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| cr1901 | _florent_: Did you get a chance to confirm the bug? If not, should I open an issue anyway? | 15:37 |
| cr1901 | bisecting could potentially, be difficult, but I'll try | 15:38 |
| sensille | zyp: do you write your own linuxcnc drivers, or intend to do so? | 15:39 |
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| zyp | sensille, yes, I did | 15:43 |
| sensille | from scratch or by starting from the existing mess? | 15:44 |
| zyp | I was looking at a few existing drivers for inspiration, but wrote it from scratch | 15:44 |
| sensille | that is quite the feat :) | 15:44 |
| zyp | I think I took a fairly unconventional approach: https://paste.jvnv.net/view/xgWVd :) | 15:46 |
| tpb | Title: JVnV Pastebin – View paste – Untitled (at paste.jvnv.net) | 15:46 |
| sensille | still trying to port to colorlight ... etherbone just works, but the cpu doesn't seem to run | 17:29 |
| _florent_ | cr1901: sorry, haven't had time yet, you can open an issue | 17:49 |
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| zyp | sensille, what type of uart are you using for the bios console? have you checked it's not just waiting for uart flow control? | 18:50 |
| zyp | a regular hardware uart will output bytes regardless of whether anybody are listening or not, but e.g. the crossover uart will block until it's polled | 18:51 |
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| cr1901 | _florent_: Ack, will do when I get the chance | 19:39 |
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| _florent_ | sensille: with the crossover uart, you can use this to avoid it being blocked at startup: https://github.com/360nosc0pe/scope/blob/main/sds1104xe.py#L134 | 20:32 |
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| sensille | nice. i don't use a bios, though. just a short loop that is supposed to blink the led. i guess i need to learn to simulate with litex. for some miracle that wasn't necessary yet | 21:05 |
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