Mmm, we seem to be talking in circles. I'll leave the nomenclature for others. But I have some experience in drawing Linux frame buffers and updating Eink displays.
Android draws on Linux framebuffers, like /dev/graphics/fb0. Tell Android Canvas.drawCircle and it does make pixels change in the frame buffer. The actual circle is usually drawn by the Qualcomm GPU (Adreno and others). But it could just as well be drawn strictly in software.
If you've got a CRT or LCD you will see the circle immediately. You can do a screen grab and you will see the circle. An Eink panel remains as it was, without the circle.
Onyx uses ioctl(fd, SET_EBC_SEND_UPDATE, struct mxcfb_update_data *update) to actually update the Eink. The pedigree of this dates back to Freescale iMX6 processor I believe, which was specifically designed for Eink.
Underlying this in simple Onyx I presume is simple software scanning the frame buffer, calculating changes and issuing waveforms to the Eink.
Underlying the "fancy-schmancy" Onyx I presume is something taking the LCD data directly off the Qualcomm chip and doing the differences and the updates itself. Such a process would be akin to the Mira which takes in HDMI or DisplayPort.
The easiest way to check this hypothesis would be to examine the pin/pad multiplexor on the Qualcomm to see if the LCD lines are being used.
I wrote multiplexor dump programs for the OMAP and the iMX6 processors. The problem with doing this for the Qualcomm SDM662 is a lack of documentation on the mux. If anyone knows where it is...
If somebody has one of the BSR units open, I'd appreciate a good photo. If, as the Onyx graphics shows, this uses a leaded package it would be easy to scope out the pins. And if anybody wants to donate a BSR unit with a broken screen...
Edit: ottischwenk had pointed out
here the chips being used for BSR. The FCC photos show them to be BGA packages (i.e. with tiny connections underneath). This would be difficult to do any sleuthing with hardware-wise.