[opensuse-arm] openQA generalhw backend

Hello, I am looking through openQA sources and I am very excited about generalhw backend. I see that it is currently in use at openqa.opensuse.org to test Raspberry Pi images. Unfortunately, there is a little details in the sources, I only see that the backend calls some preconfigured external commands to manipulate hardware, but I've failed to find more implementation details. Is there a kind of presentation or documentation on how all this works? I am especially interested in how the flash card image is deployed? -- With best regards, Matwey V. Kornilov