Re: question on armhf color depth

[Diego Roversi <diegor@tiscali.it>]

On Sun, 9 Apr 2017 22:21:43 -0400
Gene Heskett <gheskett@shentel.net> wrote:

> I note there's a link to a help site at the top of /boot/config.txt, so I 
> went thru the motions of setting it for a 1366x768, 32 bit screen. But 
> on the reboot it was just noticably slower, and xwininfo now says its a 
> 24 bit screen.  And the screen update rate is halved, to about 3 frames 
> a second.

  You should consider also that the frame buffer is stored in the ram, and the gpu had to read like 60 times for seconds to send to the monitor. It means that it consume 1366*768*3 (24bit) *60 (hz) byte per second of ram bandwith, almost 200MB/s. And it looks that max ram bandwith of the raspberry pi3, is around 1300MB/s. Reducing depth colors can give you a small speed up (at least if your application use a lot of ram) 

PS: 32bit sometime is really 24bit, with a byte wasted. It's sometimes used because usually cpu read 16/32/64 bit at a time, so you can see 32bit in the framebuffer, and still having X saying 24 bit. 

-- 
Diego Roversi <diegor@tiscali.it>