Allow wider range of USB maxPacketSize values #441
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The USB specification's allowed endpoint maxPacketSize values vary depending on the type of endpoint. In the isochronous case, it is important to allow sizes in between the ones encoded in the hardware, to efficiently use the bus bandwidth allocated for periodic transfers.
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jbeaurivage
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The USB specification's allowed endpoint maxPacketSize values vary depending on the type of endpoint. In the isochronous case, it is important to allow sizes in between the ones encoded in the hardware, to efficiently use the bus bandwidth allocated for periodic transfers.
kaizensparc
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Dec 24, 2021
The USB specification's allowed endpoint maxPacketSize values vary depending on the type of endpoint. In the isochronous case, it is important to allow sizes in between the ones encoded in the hardware, to efficiently use the bus bandwidth allocated for periodic transfers.
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This is important for isochronous endpoints, which reserve bandwidth on the USB as opposed to bulk endpoints which use whatever bandwidth is available. Isochronous transfers on full-speed USB can have maximum packet sizes anywhere between 1B and 1023B (not just powers of 2), but for instance bulk ones need to be either 1B, 2B, ... 32B, or 64B.
I've opened rust-embedded-community/usb-device#71 in usb-device to propose checking for valid endpoint sizes there, since that code will be the same across all implementations.
(note the old
alloc_ep()code made buffers at least 64B - I couldn't find a reason for that, and it seems to work fine for smaller ones)