XO 4 HDMI Debug
From OLPC
Some notes for testing the HDMI Interface of the XO-4 laptop.
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[edit] Setup
If you have access to Q7B05 or later, you can install it on the test laptop and avoid the older setup which required Linux involvement to setup HDMI.
[edit] Older Setup
Start with an XO-4 laptop running the latest firmware ( Q7B04 ). It should have a second serial port connected. You will want to download the following two pieces of software and place them on a USB stick:
Install the zImage file as /boot/vmlinuz using the following OFW command:
ok copy u:\zImhdmi int:\boot\vmlinuz
Type y when it asks if it is OK to overwrite the existing file.
Boot Linux. Then mount the USB key and install hdmi_ctl into the local directory:
mount /dev/sda1 /mnt cp /mnt/hdmi_ctl . chmod a+x hdmi_ctl
[edit] Video Init
If using OFW q7b05 or later, you can initialize the HDMI output using one of the following three commands:
ok> 720p ok> 1080p ok> d# 640 d# 480 " start-hdmi" $call-screen
A list of the supported resolutions is available in the OFW source code.
[edit] Using Linux
At this point, you can initialize HDMI output from within Linux:
./hdmi_ctl
When this starts, you can set video output at a particular resolution using:
>> sv 14
That will select 720p on your HDMI monitor. "sv 24" will get you 1080p, "sv 25" will get 640x480.
[edit] Patching CForth
In order to manipulate the video parameters in real time, we use a second serial port connected to CForth running on the security processor. It must be enabled by holding down the "rotate" key while booting. Then start ofw using the command:
ok dbg ofw
The following forth commands need to be downloaded (over the second serial port):
: w1 20b000 + io! ; : r1 20b000 + io@ ; : video-on 104 r1 44 w1 fc r1 3c w1 f4 r1 34 w1 80 r1 100 or 80 w1 ; alias v video-on : +hdmi 20bc00 + ; : hdmi! +hdmi io! ; : hdmi@ +hdmi io@ ; : hdmi-i! ( b reg# -- ) swap 0 hdmi! h# 8000.0000 or 4 hdmi! ; : hdmi-i@ ( reg# -- b ) h# 4000.0000 or 4 hdmi! 0 hdmi@ ; alias r hdmi@ alias w hdmi! alias ii hdmi-i! alias ir hdmi-i@ : access-phy h# 20 hdmi@ 1 or h# 20 hdmi! ; alias phy access-phy : access-3d h# 20 hdmi@ 1 invert and h# 20 hdmi! ; alias 3d access-3d
And these allow for easier manipulation of the PHY0 and PHY1 registers:
6 value damp 5 value eamp 2 value cp : phy0 damp o# 1111 * eamp o# 11110000 * or cp h# 55000000 * or 8 w ; 0 value ajd 1 value svtx 9 value idrv : phy1 ajd h# f0000000 * svtx o# 1111 * d# 16 lshift or idrv h# 1111 * or h# c w ;
These will need to be downloaded again after turning the laptop off.
You can use these patches to manipulate the PHY registers by typing:
phy phy0 phy1
Display some video using
v
[edit] Changing PHY Settings
You must rerun CForth register settings after using hdmi_ctl, 720p, or 1080p. After changing the resolution with hdmi_ctl, you must re-run:
phy phy0 phy1
In order to change a value, change the associated variable and then re-write the related register. To change DAMP to 3:
3 to damp phy0
To change IDRV to 4:
4 to idrv phy1
Note: There is hysteresis in the PHY circuit. Once you pass a certain threshold, you can't return simply by reducing the value. If you are close to a critical point, increasing a parameter by 1 may result in a change such that then reducing that parameter by 1 doesn't restore us to the same output. In many cases, the parameter must be reduced by 3 then increased by 2 o restore the same output.
