Converter setup protocol

The Blackmagic design Mini and Micro converters have an USB port for firmware updates and some basic configuration.

The firmware update side is handled through the standardized DFU protocol and the the .bin files for the converters are distributed with the offical setup applications. These can be extracted from the installer and flashed using the regular dfu-utils methods.

The configuration protocol

The protocol for configuration is quite simple but it does require knowing in advance which settings exist on the specific hardware and what the possible values are. This is hardcoded in the offical application.

The full protocol is build on top of control transfers. The settings are split up in two categories. The only difference between these is different bmRequestType and bRequest values to read and write from them.

	System setting	Device setting
bmRequestType r/w	0xA1 / 0x21	0xC0 / 0x40
bRequest transaction	1	10
bRequest name	2	11
bRequest read	3	12
bRequest write	4	13

The system settings are the device name, software version and build id. All the other settings are device settings.

To do a setting read or write it is first required to get a transaction id. The transaction id is changed after every single read and write to the device.

Type	Control Transfer
bmRequestType	0xA1 or 0xC0	Depends on system/device setting
bRequest	1 or 10	Depends on system/device setting
wValue	0x0000
wIndex	0x0000
wLength	2

The result is a 2-byte transaction number that is required fo the further control transfers.

Reading a setting

A setting read is done by first writing the ascii name of the setting to the device with a control transfer and then reading back the result. Here is an example for reading the device name:

Type	Control Transfer
bmRequestType	0xA1	Because DeviceName is a system setting
bRequest	2	bRequest for setting name
wValue	xxx	This is the transaction ID
wIndex	0x0000
wLength	10
Data	DeviceName	Name of the setting

Now the value can be read back by doing another control transfer

Type	Control Transfer
bmRequestType	0x21	Because DeviceName is a system setting
bRequest	3	bRequest for setting read
wValue	xxx	This is the transaction ID
wIndex	0x0000
wLength	255	Max length of the name

The resulting data will be the value of the setting.

Writing a setting

A setting write is done by writing the name of the setting with a control transfer and then writing the value of that setting with another control transfer.

Here is an example for writing the device name:

Type	Control Transfer
bmRequestType	0xA1	Because DeviceName is a system setting
bRequest	2	bRequest for setting name
wValue	xxx	This is the transaction ID
wIndex	0x0000
wLength	10
Data	DeviceName	Name of the setting

This control transfer was identical to the first control transfer for a setting read above.

Now the value needs to be written by a second control transfer:

Type	Control Transfer
bmRequestType	0xA1	Because DeviceName is a system setting
bRequest	4	bRequest for setting write
wValue	xxx	This is the transaction ID
wIndex	0x0000
wLength	7
Data	Example	Sets the name to “Example”