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doc:appunti:hardware:mini_pc_intel_pentium_j3710 [2026/02/22 18:20] – [Kernel 6.1] niccolodoc:appunti:hardware:mini_pc_intel_pentium_j3710 [2026/02/24 19:12] (current) – [DPMS (Display Power Management Signaling)] niccolo
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 </code> </code>
  
-Despite the HDMI monitor is connected, the status pseudfile reports that it is disconnected:+Despite the HDMI monitor is connected, the status pseudfile reports that it is **disconnected**:
  
 <code> <code>
Line 37: Line 37:
 </code> </code>
  
-Writing the **on** string to the file causes a kernel trace:+Writing the **on** string to the file changes the status to connected:
  
 <code> <code>
 echo on > /sys/class/drm/card0-HDMI-A-1/status echo on > /sys/class/drm/card0-HDMI-A-1/status
 +cat /sys/class/drm/card0-HDMI-A-1/status
 +connected
 </code> </code>
 +
 +but it causes a kernel trace:
  
 <code> <code>
Line 47: Line 51:
 </code> </code>
  
 +When the **i915** kernel module is loaded, you can find five **DRM** (Direct Rendering Manager) devices managed by **card0**:
 +
 +<code>
 +ls -1 /sys/class/drm/
 +card0
 +card0-DP-1
 +card0-DP-2
 +card0-HDMI-A-1
 +card0-HDMI-A-2
 +card0-HDMI-A-3
 +renderD128
 +version
 +</code>
 +
 +It is possibile to do a **complete hardware reset** of the cards using the following command:
 +
 +<code>
 +echo "0000:00:02.0" > /sys/bus/pci/drivers/i915/unbind
 +sleep 1
 +echo "0000:00:02.0" > /sys/bus/pci/drivers/i915/bind
 +</code>
 +
 +After the //unbind// you can verify that the directory **/sys/class/drm/** is empty, it will be populated again after the //bind//.
 +
 +===== Blanking the Virtual Terminal =====
 +
 +When the host is started in frame buffer text console, the **setterm** command can be used to force the screen to go blank:
 +
 +<code>
 +setterm --blank force
 +setterm --powerdown 0
 +</code>
 +
 +The monitor turns off due no signal and remains blank even keys are pressed on the keyboard.
 +
 +To revive the screen:
 +
 +<code>
 +setterm --blank poke
 +setterm --powerdown 0
 +</code>
 +
 +If the screen is blanked the following command returns **1**:
 +
 +<code>
 +setterm --blank
 +1
 +</code>
 +
 +==== DPMS (Display Power Management Signaling) ====
 +
 +DPMS (Display Power Management Signaling) is a VESA standard used to reduce monitor power consumption by controlling power states (On, Standby, Suspend, Off) generally based on user inactivity.
 +
 +It is possible to control the status of the display connected to the frame buffer writing some values to the pseudo file:
 +
 +<code>
 +echo 4 > /sys/class/graphics/fb0/blank
 +echo 0 > /sys/class/graphics/fb0/blank
 +</code>
 +
 +| 0  | FB_BLANK_UNBLANK  | Screen ON (normal operation)  |
 +| 1  | FB_BLANK_NORMAL  | Blank screen (no power saving)  |
 +| 2  | FB_BLANK_VSYNC_SUSPEND  | Suspend vertical sync  |
 +| 3  | FB_BLANK_HSYNC_SUSPEND  | Suspend horizontal sync  |
 +| 4  | FB_BLANK_POWERDOWN  | Power down display (DPMS off)  |
 +
 +Writing the value 4 to the pseudodevice changes the **DPMS** property from **On=0** to **Off=3**. It is possibile to check all the **connectors properties** using **modetest** (provided by the **libdrm-tests** Debian package):
 +
 +<code>
 +modetest -M i915 -c
 +opened device `Intel Graphics` on driver `i915` (version 1.6.0 at 20201103)
 +Connectors:
 +id      encoder status          name            size (mm)       modes   encoders
 +95      94      connected       HDMI-A-1        0x0             5       94
 +  modes:
 +        index name refresh (Hz) hdisp hss hse htot vdisp vss vse vtot
 +  #0 1024x768 60.00 1024 1048 1184 1344 768 771 777 806 65000 flags: nhsync, nvsync; type: driver
 +  #1 800x600 60.32 800 840 968 1056 600 601 605 628 40000 flags: phsync, pvsync; type: driver
 +  ...
 +    2 DPMS:
 +        flags: enum
 +        enums: On=0 Standby=1 Suspend=2 Off=3
 +        value: 3
 +    ....
 +
 +107     106     connected       HDMI-A-2        470x260         30      106
 +  modes:
 +        index name refresh (Hz) hdisp hss hse htot vdisp vss vse vtot
 +  #0 1024x600 59.82 1024 1068 1156 1344 600 603 609 625 50250 flags: phsync, nvsync; type: preferred, driver
 +  #1 1920x1080 60.00 1920 2008 2052 2200 1080 1084 1089 1125 148500 flags: phsync, pvsync; type: driver
 +  ...
 +    2 DPMS:
 +        flags: enum
 +        enums: On=0 Standby=1 Suspend=2 Off=3
 +        value: 3
 +    ....
 +</code>
 +
 +
 +FIXME What is this?
 +
 +<code>
 +/usr/sbin/vbetool dpms on
 +/usr/sbin/vbetool dpms off
 +</code>
 +
 +
 +===== Pygame =====
 +
 +We verified what driver uses the Pygame app:
 +
 +<code python>
 +import pygame
 +pygame.init()
 +print(pygame.display.get_driver())
 +</code>
 +
 +It says **KMSDRM**.
 +
 +Using that driver the SDL **Simple DirectMedia Layer** library owns the DRM master, external tools (modetest, sysfs) do not work for blanking the screen. The correct solution is to control this from inside SDL.
 +
 +===== HDMI Monitor supported modes =====
 +
 +<code>
 +cat /sys/class/drm/card0-HDMI-A-1/modes
 +</code>
 +
 +<code>
 +1024x600
 +800x600
 +800x600
 +800x600
 +800x600
 +720x576
 +...
 +</code>
 +
 +<code>
 +fbset -i -fb /dev/fb0
 +
 +mode "1024x600"
 +    geometry 1024 600 1024 600 32
 +    timings 0 0 0 0 0 0 0
 +    rgba 8/16,8/8,8/0,0/0
 +endmode
 +
 +Frame buffer device information:
 +    Name        : i915drmfb
 +    Address     : 0
 +    Size        : 2457600
 +    Type        : PACKED PIXELS
 +    Visual      : TRUECOLOR
 +    XPanStep    : 1
 +    YPanStep    : 1
 +    YWrapStep   : 0
 +    LineLength  : 4096
 +    Accelerator : No
 +</code>
doc/appunti/hardware/mini_pc_intel_pentium_j3710.1771780845.txt.gz · Last modified: by niccolo