Hi,
Am 10.06.2015 um 17:58 schrieb Michael Mrozek EvilDragon@openpandora.org:
Am Mon, 8 Jun 2015 11:10:39 +0300 hat Tomi Valkeinen tomi.valkeinen@ti.com geschrieben:
Hi,
We now have enabled a TE impulse from the ssd2858 chip going to dsiporta_te0 / gpio6_189. The question is how to enable it on the OMAP5 side.
I presume you are using the SSD2858 with DSI video mode input. There's no TE in that case. TE is only for DSI command mode.
I browsed the net quite a bit, trying to find out the differences between video mode, command mode and TE.
If I understand it correctly, TE mode is always only available in command mode (on any SoC, not just on the OMAP). So TE is officially for anti-tearing and only works in command mode - therefore, I wanted to find out what the differences are between video mode and command mode.
I found that site, which does explain it quite good: http://www.electronicproducts.com/Analog_Mixed_Signal_ICs/Communications_Int...
If I understand correctly, video mode is basically the same as the classic way (sending RGB signals). There's always a video stream being sent, usually without an external framebuffer, so unless you use the timings from the video stream, it's not possible to sychronize them (that's why TE doesn't work here).
Command mode has a different approach: It sends the frames as DCS packages to the LCD (or SSD in our case). The SSD/LCD needs to have a framebuffer to store it, displays it autonomously and then sends a TE signal back to the OMAP5 to tell it that the next package can be sent.
The SSD definitively has a frame buffer (where it reads the rotated image from) so it should be capable of command mode. Especially since it supports the TE output (and some DCS commands to program the scan line where TE impulses start).
Additionally, command mode supports stuff like only updating video data when necessary (i.e. if a smartphone shows a website without animation and the user doesn't scroll around, it doesn't to send frame packages and saves power).
First question: Did I understand that correctly, or is there something wrong?
From my (also not complete) experience and knowledge: yes
Second question: Can we use the command mode on the OMAP5? Is this implemented in the driver? Does the driver (and the hardware) take care of everything or would we need to fix every program on Linux to make it work with the command mode?
That is the key question. Or to reformulate / add questions:
* can command mode be used together with omapfb i.e. /dev/fb? * how fast is command mode compared to video mode? Same speed or slower?
BR, NIkolaus