allow custom bcd usb version #3599
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embassy-usb/src/descriptor.rs
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| config.device_sub_class, // bDeviceSubClass | ||
| config.device_protocol, // bDeviceProtocol | ||
| config.max_packet_size_0, // bMaxPacketSize0 | ||
| (config.bcd_usb >> 8) as u8, // bcdUSB |
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the 0x10 above is also part of bcd_usb, it's the lower byte. for example USB 2.1 is 0x0210.
The config default should also be 0x0210 instead of 0x02
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what's the use case for this? in what cases do you want to force the USB version down to 2.0 or 1.x? Would these use cases still be satisfied if the API was a "usb version" enum instead of a freeform u16? IMO that'd be more user-friendly because it'd prevent invalid values. Also, do we need to disable some features that weren't available in older USBs? |
I think in many cases where you are trying to emulate a specific device. When using 2.1 the host assumes you are using a bos_descriptor since that is what 2.1 is. By forcing the use of 2.0 you are disabling unused features. Maybe the same is true for 1.x, but I'm not sure what other changes might be required for that use case.
I think so, I can easily create one for 2.1, and 2.0 and others can include others when needed.
In my testing, no everything seems to work as is. |
embassy-usb/src/builder.rs
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| /// Device BCD USB version. | ||
| /// | ||
| /// Default: `0x0210` ("2.1") | ||
| pub bcd_usb: BcdUsbVersion, |
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I'd name this just UsbVersion.
"BCD" is a reference to Binary Coded Decimal, ie how it's coded in binary. if it's an enum the user no longer cares about that.
Allows a custom bcdusb version like 1.1 (0x011) but leaves the default to 2.0/2.1