I'm having some trouble changing the display resolution on the AM3358. We're running the Linux kernel/filesystem that's provided with the Sitara SDK 07.00.00.00 (although with slight modifications for our custom board).
We need to be able to adjust the display resolution without rebooting. I know I've had this working before, but now I'm having difficulties getting this to work. Let me describe a couple scenarios that exhibit problems.
Scenario 1
My device tree is configured for 640x480 resolution, and the system boots properly to this. Here are the settings in the device tree file:
hactive = <640>; vactive = <480>; hback-porch = <48>; hfront-porch = <16>; hsync-len = <96>; vback-porch = <33>; vfront-porch = <10>; vsync-len = <2>; clock-frequency = <25175000>; hsync-active = <0>; vsync-active = <0>;
After booting up, here is the output of the fbset command (displaying the current settings):
mode "640x480-60"
# D: 25.176 MHz, H: 31.469 kHz, V: 59.942 Hz
geometry 640 480 640 480 32
timings 39721 48 16 33 10 96 2
rgba 8/16,8/8,8/0,8/24
endmode
This looks to be correct. Also, when I observe the CTRL register in the LCD controller, the clkdiv field is 2. Now, I change to an 800x600 mode with fbset -xres 800 -yres 600 -vxres 800 -vyres 600 -t 25000 88 40 23 1 128 4. I again dump the video mode info from fbset:
mode "800x600-60"
# D: 40.000 MHz, H: 37.879 kHz, V: 60.317 Hz
geometry 800 600 800 600 32
timings 25000 88 40 23 1 128 4
rgba 8/16,8/8,8/0,8/24
endmode
This also looks appropriate. Now, I want to switch back to 640x480, so I issue fbset -xres 640 -yres 480 -vxres 640 -vyres 480 -t 39722 48 16 33 10 96 2, which results in the following:
mode "640x480-63"
# D: 26.667 MHz, H: 33.333 kHz, V: 63.492 Hz
geometry 640 480 640 480 32
timings 37500 48 16 33 10 96 2
rgba 8/16,8/8,8/0,8/24
endmode
Notice that the pixel clock is no longer 39721 but 37500, which changes the vertical refresh from about 60 Hz to about 63.5 Hz. The clkdiv field of the CTRL register is now set to 3, not 2 as when first booted. What happened here?
Scenario 2
I'm booting up with a resolution of 480x272, which is the resolution used by default in the TI SDK. After booting, I dump the video info:
mode "480x272-75"
# D: 12.000 MHz, H: 22.430 kHz, V: 75.268 Hz
geometry 480 272 480 272 32
timings 83333 43 8 12 4 4 10
rgba 8/16,8/8,8/0,8/24
endmode
This looks right. I then try to set 640x480 using the same command and timing information from scenario 1 above: fbset -xres 640 -yres 480 -vxres 640 -vyres 480 -t 39722 48 16 33 10 96 2, and then again dump the fbset info:
mode "640x432-66"
# D: 25.173 MHz, H: 31.466 kHz, V: 65.967 Hz
geometry 640 432 640 432 32
timings 39725 48 16 33 10 96 2
rgba 8/16,8/8,8/0,8/24
endmode
Notice here that we're actually in a 640x432 mode! When I first boot into 480x272 mode, the clkdiv field of the CTRL register is 2 and the vertical refresh rate is 75 Hz. After switching to 640x480, it's still at 2. However, when I switch back from 640x480 to 480x272, clkdiv is now 4, and the vertical refresh rate is 79 Hz instead of 75 Hz (while the other registers are identical).
I've also tried booting into 800x600 and then setting 640x480 (using the exact same command above), but I actually get 640x345 for some weird reason.
When I thought I had this working, I asked another question in this forum about unloading/reloading the PVR drivers while switching modes, but haven't received a response yet (and now I seem to have taken a step backwards). The information there might be useful to this discussion though.
SUMMARY
- It appears that the clkdiv field of the CTRL register in the LCD controller isn't being set properly.Sometimes, the number of vertical lines is not set properly.Depending on what video mode I boot into and subsequently switch to, I can get different results, even for the same modes.
