silly projects I would implement if I had the know-how: PCIe-over-USB
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Replying to @hikari_no_yume
USB doesn't provide DMA, I believe? But why should that stop me.
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Replying to @hikari_no_yume
you can't do PCIe over USB because the former needs a hard worst-case latency guarantee and the latter explicitly avoids one
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Replying to @whitequark @hikari_no_yume
Wait, PCIe has latency guarantees? Didn't
@marcan42 tunnel PCIe over some crazy-slow setup for PS4 stuff and have it work fine?2 replies 0 retweets 1 like -
I believe yes, see PCIe Base Specification 3.5.2.1 and Table 3-4
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Replying to @whitequark @11rcombs and
I'm sure you could work around that if you can control the entire system, like by gating the TLP Transmitter's clock
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ahahaha
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or maaaaybe by terminating PCIe on either end and then using flow control to effectively stall the transmitter? no idea about PS4
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You do not tunnel the data link layer. Those timeouts are for TLP transmission acks, not TLP to completion (which is what we care about).
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Replying to @marcan42 @whitequark and
For comparison, USB has tight reply ACK timing requirements too (but nobody who isn't writing a USB device controller has to deal with that)
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For PCIe, the section you want to look at is 2.8. Note how it doesn't say much. Table 7-25 has the actual values. >10ms is recommended (!)
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thanks!
0 replies 0 retweets 1 likeThanks. Twitter will use this to make your timeline better. UndoUndo
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