PORTS Forum

Ports and Interfaces => USB => Topic started by: jb on September 06, 2018, 02:34:26 pm

Title: Is bcdDevice v1.23 or v1.2.3?
Post by: jb on September 06, 2018, 02:34:26 pm: If bcdDevice is 0x0103

macOS System Report displays it as "Version: 1.03"

NirSoft USBDeview displays it as "1.03"

But I thought it was conceptually "1.0.3".

USB 3.2 spec says

Quote
The bcdUSB field contains a BCD version number. The value of the bcdUSB field is 0xJJMN for version JJ.M.N (JJ - major version number, M - minor version number, N - sub-minor version number), e.g., version 2.1.3 is represented with value 0213H and version 3.0 is represented with a value of 0300H.

and Beyond Logic (https://www.beyondlogic.org/usbnutshell/usb5.shtml) says

Quote
The value is in binary coded decimal with a format of 0xJJMN where JJ is the major version number, M is the minor version number and N is the sub minor version number.

Quote
The bcdDevice has the same format than the bcdUSB and is used to provide a device version number.
Title: Re: Is bcdDevice v1.23 or v1.2.3?
Post by: Jan Axelson on September 06, 2018, 02:38:07 pm: The spec is the final authority. 1.0.3 is correct.
Title: Re: Is bcdDevice v1.23 or v1.2.3?
Post by: jb on September 06, 2018, 02:45:59 pm: Well the spec doesn't explicitly say "bcdDevice uses the same format as bcdUSB" that I can find. It just says "binary-coded decimal". Beyond Logic says they're the same format, but isn't official.

Also found XMOS document (https://www.xmos.com/published/usb-audio-software-design-guide) that says

Quote
BCD_DEVICE Description Device firmware version number in Binary Coded Decimal format: 0xJJMN where JJ: major, M: minor, N: sub-minor version number. ... Default: XMOS USB Audio Release version (e.g. 0x0651 for 6.5.1).
Title: Re: Is bcdDevice v1.23 or v1.2.3?
Post by: bpaddock on September 07, 2018, 08:20:02 am: The LUFA project uses this:

https://github.com/abcminiuser/lufa/blob/master/LUFA/Drivers/USB/Core/StdDescriptors.h

/** Macro to encode a given major/minor/revision version number into Binary Coded Decimal format for descriptor
          * fields requiring BCD encoding, such as the USB version number in the standard device descriptor.
          *
          * \note This value is automatically converted into Little Endian, suitable for direct use inside device
          * descriptors on all architectures without endianness conversion macros.
          *
          * \param[in] Major Major version number to encode.
          * \param[in] Minor Minor version number to encode.
          * \param[in] Revision Revision version number to encode.
          */
         #define VERSION_BCD(Major, Minor, Revision) \
           CPU_TO_LE16( ((Major & 0xFF) << 8) | \
           ((Minor & 0x0F) << 4) | \
           (Revision & 0x0F) )
Title: Re: Is bcdDevice v1.23 or v1.2.3?
Post by: Jan Axelson on September 07, 2018, 03:25:39 pm: Lacking any evidence to the contrary in the specs, I believe it is safe to assume that both "bcd" fields use the same format.