Gert's VGA add-on for the B+

[dom]

@civic95man
Yes, pixelclock will need to include any cycles, whether there are active pixels or blanking.

[cosjava]

My Gert`s VGA adapter works... almost as I wanted. I am not able to make them work in the same time with GUI!

I would like to expand my GUI using "two independent screens" as showed in the video at
https://www.raspberrypi.org/gert-vga-adapter/
I would like to expand my GUI using both screens - not working at the moment.

When I use the following line in config.txt, after the boot the GUI works well through VGA adapter.
display_default_lcd=1
However when I comment that line with hash (#) after the boot the GUI works well through HDMI adapter.

The only thing that has worked in the same time with both screens is watching a video clip by following way:
I have booted the GUI using VGA adapter.

My config.txt is following:

hdmi_group=1
hdmi_mode=16
hdmi_force_hotplug=1
hdmi_edid_file=1
#This causes to use the whole scree and have pixel-to-pixel ration no scaling
disable_overscan=1

enable_dpi_lcd=1
dpi_group=2
dpi_mode=36
display_default_lcd=1
dpi_output_format=5

Can you help me?

[cosjava]

Something to add to my previous post. I am able to watch a video from HDMI screen and using the GUI on LCD screen. However the desktop does not work with both screens in the same time.

I have booted the system up using LCD screen for GUI by:
display_default_lcd=1

Then I am able to watch any video from HDMI screen by:
omxplayer --display 5 video.avi

[nuis]

Hello, i would need to get a rgb signal combined with a composite sync on the green channel.

I am aware that it can be done right after the analog conversion
with a quite simple circuit but would love to send the signal properly right away.

Is it possible to change the colour signal software wise before it "leaves" the pin?
I am thinking it like that:

1. Watch and combine the H and V sync to one signal.
2. Use it to alter the green channel.

Since at this point it is still all digital, i am not sure
if that will work. I still do not fully understand how the sync
behaves voltage wise (against the 0-0.7v colour information) in the analog part.

Can someone give me a slight hint if this is somehow possible,
and maybe what i should look at to get a better understanding?
I am still learning the basics of electronics, but am very eager to find out more.

Thanks.

[Gert van Loo]

"The impossible we do direct, wonders take a bit longer."

Yes, it can be done but it requires a bit more than a few resistors....
A combined SYNC + colour signal is built from taking a positive colour value and adding a negative sync.
Thus you need a negative supply and shift the sync so it is between -X and 0 volts, then add the sync to the green.
(I don't know the exact value of X)

[PiGraham]

I think you can do sync on green without a negative supply.

Here's an app note for MAXIM MAX9589 running from single 3.3V supply.

http://www.maximintegrated.com/jp/app-n ... vp/id/4116

I think this assumes black level on the video is 0.3V and the bottom of the sync is 0V. These are typical 1V video levels.
If black level is 0V on the GERTVGA666 then this simple approach will not work.

[nuis]

So please tell me if my thoughts on the sync are right.

Lets say the picture is black so the voltage of the colour signal
is 0. Now the H-Sync pulses make it negative by (guessing) 1v.
So at H-Sync pulses the colour voltage is -1v.

Now there are also the V-Sync pulses from time to time
that also make the voltage negative but less (lets say by 0,5 v)
but they are much longer. So at times of V-Sync the voltage
of the colour signal is -0.5v.

Is the amount of negative voltage, how the display knows whether
it is a H or V Sync Pulse? And everything else above 0 will be
drawn accordingly to the voltage at that particular timestep?

I am looking at this http://www.raphnet.net/electronique/syn ... een_en.php
oscilloscope picture right now, thats how i interprete this.

Now reading your post, i am not sure i understand it, sorry.
So there is no way to manipulate the green signal in digital only?
Also to shift the sync to negative? Can digital signals be negative?
There would be always more parts involved? Before the resistors or behind?
So then my only option is to go with a circuit like on the linked page.
Is that what you had in mind? Sorry for beeing complete noob and the million of dumb questions;)

Thanks

[PiGraham]

The voltage relative to ground (0V) should not go negative. H sync and Vsync pull down to 0V
For 1V video with sych black level is 0.3V , not 0V
On the GERT VGA666 black level is 0V because it just uses a resistor ladder. As long as the display ac couples the signal and clamps the black level on the 'front porch' it all works, even if you have a negative sync voltage.

[jeremydial1981]

Is there any way to use an external source as the sync (pixel clock i believe) I am working on a video switcher that will switch a single monitor between two sources. One source will be a raspberry Pi and the other source will be a computer. If I am able to use the h and v sync coming from the pc and input these to the pi as its pixel clock, I will be able to switch the video source without the monitor loosing sync and having to wait >1 sec for the monitor to re-sync and start to display.

I guess in a nutshell my question is, can the pi use an external source as the hdmi sync.

*disclaimer, I may be using the incorrect terms for some items (pixel clock etc. )

thanks for the help guys.

[mikronauts]

I am 99.9999% sure you cannot do that, as it is not needed for the functionality the LCD interface was designed for.

I just buy small cheap HDMI switches, or use the multiple HDMI inputs on TV's.

Is there any way to use an external source as the sync (pixel clock i believe) I am working on a video switcher that will switch a single monitor between two sources. One source will be a raspberry Pi and the other source will be a computer. If I am able to use the h and v sync coming from the pc and input these to the pi as its pixel clock, I will be able to switch the video source without the monitor loosing sync and having to wait >1 sec for the monitor to re-sync and start to display.

I guess in a nutshell my question is, can the pi use an external source as the hdmi sync.

*disclaimer, I may be using the incorrect terms for some items (pixel clock etc. )

thanks for the help guys.

[jeremydial1981]

I am 99.9999% sure you cannot do that, as it is not needed for the functionality the LCD interface was designed for.

I just buy small cheap HDMI switches, or use the multiple HDMI inputs on TV's.

Thanks for the reply. The device that is providing the second video signal (computer) can only output in vga. I already have the switch working great switching the monitor between the two sources. I was just thinking that If i could get the pi to use the sync pulses that are coming from the other device, it would be a smoother switch.

I am pretty sure I have read some post on here about someone using an external source for the sync clock but I have been unable to find it today.

[Gert van Loo]

I have forwarded the question.
The solution might be to use the vsync as interrupt to the GPU which then syncs the video signal to it.

[jeremydial1981]

Do you guys think it would be possible to change the linux "Driver" or change the kernel to get its pixel clock from another source?

[Gert van Loo]

The reply I received was : No.

[aBUGSworstnightmare]

Dear sirs,
I'm new to this Forum! I've just configured my Pi B+ to use the DPI with a 7in module.
Looking good for the first try. Currently 6-bit colours only but will test for full 24-bit next.

I want to know if the DPI overlay will also work when using KODI (openelec). Has anybody tested so far?

In Addition, I'm wrapping my head around the dpi_output_format.
Can anybody expalin the maths behind i.e. (for Adafruit 5in TFT)
dpi_output_format=454661

I don't understand what's the output_format and rgb_order used. Translating it to binary gives
0xd454661=0xb0110 1111 0000 0000 0101

-->
output_format = 0xb0110 = 0xd6 = DPI_OUTPUT_FORMAT_18BIT_666_CFG2
rbg_order = 1111 -> shouldn't this be 1 to 4? Or do I miss the Point?

Thanks for your Feedback, rgds
Joerg

[kirgene]

Hello,
What chip should I use to convert DPI to HDMI? I'd like to have two HDMI outputs.

[aBUGSworstnightmare]

Hello,
What chip should I use to convert DPI to HDMI? I'd like to have two HDMI outputs.

Using DPI will disable the HDMI --> no way to have dual HDMI this way, sorry.

By the way, here are two of my results:
7in with 800x480 pixels

7in TFT - 18bit RGB via DPI

WP_20150630_16_02_13_small.jpg (31.28 KiB) Viewed 12428 times

second one is a Sharp LQ060B3DW01 with 768x128 Pixels

Sharp LQ060B3DW01

WP_20150701_14_45_08_small.jpg (23.55 KiB) Viewed 12428 times

[Gert van Loo]

Using DPI will disable the HDMI --> no way to have dual HDMI this way, sorry.

That is incorrect. You can use the parallel display port at the same time as the HDMI output.
There have been videos of VGA alongside HDMI from the start.
I am not aware of any DPI to HDMI chips, but then I don't know all the chips out there.
IF there is such a device you had better be darn good at electronics, PCB design etc. to get it working.
Even with best design effort the quality might be disappointing.

[Tormak]

Hi,

I have a project, to connect a raspberry on an old CRT monitor.

I have buy the Gert Vga 666, and in theory, the CEA mode 8 display 320*240p @ 60Hz.

But in practice, the signal was 320 * 240p, H-Sync 60Hz, V-Sync about 31Khz.

But in this technology, the V-sync must be 15Khz.

Do you have an idea for obtain a V-sync @ 15khz in the config.txt ? (perhaps in "hdmi_timings" ?)

Thx in advance.

Ps : Sorry for my children english, it's not my primary language !

Tormak.

[WalkToFreedom]

Hi,

I have a project, to connect a raspberry on an old CRT monitor.

I have buy the Gert Vga 666, and in theory, the CEA mode 8 display 320*240p @ 60Hz.

But in practice, the signal was 320 * 240p, H-Sync 60Hz, V-Sync about 31Khz.

But in this technology, the V-sync must be 15Khz.

Do you have an idea for obtain a V-sync @ 15khz in the config.txt ? (perhaps in "hdmi_timings" ?)

Thx in advance.

Ps : Sorry for my children english, it's not my primary language !

Tormak.

This is exactly what I am trying to do also. I got the idea from http://celso.io/2012/12/17/connecting-a ... nitor.html but you can see they use a GBS 8100 which will downscale to 15hz. Then I came across the VGA666 and I wondered if the circuit/software/driver could be modified to output at 15hz. This would then replace the GBS 8100 and the HDMI to VGA converter! and make a ton of Retro gamers happy as all over the net people are looking for a solution to replace the need to have a PC with dedicated video card and or all these extra components.

I actually email Gert via his website and I got this response from Nick:

Hi Matt

Im looking after Gerts website for a while, but im afraid im not an expert on his stuff. I did work on the broadcom chip though.

Gerts vga board is just a simple resistor ladder A to D converter that turns the parallel digital outputs of the DPI block into analogue signals. So you have 3 colours and 2 syncs which should be enough to drive your display.

I would think it is quite possible to change the DPI settings so that it runs at the required frame rate and X-Y size to drive
your monitor, although I havent checked to make sure it can go that low. It was supposed to drive small lcd displays though so i suspect that it can.

However you would potentially have to set up other graphics components in the system to produce the required size of display (x by y pixels) if this isnt already supported.

So as far as I know the V3D will be generating screen images of a fixed X-Y size in memory that contain the screen contents.
The Video scaler will be scaling and compositing several layers of these images into a screen resolution output stream that is sent to the DPI for outputting. Changing all of this is certainly possible but way outside my field of knowledge.

It may be possible to simply reprogram the scaler to scale the images to the required size, and the DPI to output them. I think this would be a question for one of the video experts on the Pi forums as its mainly going to be a software issue.

best of luck
Nick

Would be great to hear peoples thoughts on this as in the Arcade Cab scene this is a big problem for those wishing to use a CRT in their cab and wanting to capture the original 240p look.

P.S I do actually have a working PC ArcadeVGA setup working with a re-purposed CRT to telly via SCART and a 'dodgy diode' circuit but I have bought a Pi2 to give it a go.

Thanks! Matt

[dom]

I have buy the Gert Vga 666, and in theory, the CEA mode 8 display 320*240p @ 60Hz.

But in practice, the signal was 320 * 240p, H-Sync 60Hz, V-Sync about 31Khz.

But in this technology, the V-sync must be 15Khz.

Do you have an idea for obtain a V-sync @ 15khz in the config.txt ? (perhaps in "hdmi_timings" ?)

Have you tried configuring hdmi_timings to produce the signal you want? In theory that should work (as long as none of the setting go out of spec).
Work out the timings that are required and I'll check if they should be supported.

[WalkToFreedom]

Have you tried configuring hdmi_timings to produce the signal you want? In theory that should work (as long as none of the setting go out of spec).
Work out the timings that are required and I'll check if they should be supported.

Hi dom. I'm very much a noob (my Pi2 just arrived yesterday) but I found your thread viewtopic.php?p=235430

There is an interesting discussion (maybe outdated?) about HDMI timings in the comments section off the previous article I posted about with the Pi starting here:

http://hackaday.com/2012/12/17/using-ar ... ent-905500

I have no idea where to find the timings for the TV? Service manual? I guess I need to find out the horizontal and vertical blanking times etc? Is it possible to set something up as a base and tweak via trail and error?

I found this article which does a good job of explaining modelines which I think equates to the hdmi_timings?

http://easymamecab.mameworld.info/html/monitor6.htm

[WalkToFreedom]

Well, it seems that it wasn't quite so complicated after all (unless I have missed something). Pretty sure I've got it outputting 240p to my TV without the need for the GBS-8100. Here's how I did it.

1. I bought an active HDMI to VGA convertor.
2. I made the 'dodgy diode' circuit to join the two syncs as shown here: http://members.optusnet.com.au/eviltim/scart.htm (I think this now is more commonly know as SyncStrike?)
3. I changed/added these settings in config.txt:

Code: Select all

disable_overscan=1
framebuffer_width=320
framebuffer_height=240
hdmi_force_hotplug=1
hdmi_group=1
hdmi_mode=8
config_hdmi_boost=4
hdmi_ignore_edid=0xa5000080
hdmi_ignore_edid_audio=1
hdmi_ignore_cec=1
hdmi_pixel_encoding=2
sdtv_aspect=1

I still have problems displaying the games in their native resolutions but I think this is more to do with MAME / front end than the Pi, maybe because the Pi is missing those resolutions, I guess I could add them?

[aBUGSworstnightmare]

Here's a config.txt for a Sharp 8.4in VGA panel - LQ084V1DG43

Code: Select all

# For more options and information see 
# http://www.raspberrypi.org/documentation/configuration/config-txt.md
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1

# uncomment to force a console size. By default it will be display's size minus
# overscan.
framebuffer_width=640
framebuffer_height=480

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800


# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
overscan_left=0
overscan_right=0
overscan_top=0
overscan_bottom=0
  
# Disable spi and i2c, we need these pins.
dtparam=spi=off
dtparam=i2c_arm=off
 
# enable the DPI display
enable_dpi_lcd=1
display_default_lcd=1

# ---------------------------------------------
# DPI output format definitions
# https://www.raspberrypi.org/forums/viewtopic.php?p=628061#p628061
# DPI structure: https://www.raspberrypi.org/forums/viewtopic.php?p=617719#p617719
# ---------------------------------------------
# output_format:
#   1: DPI_OUTPUT_FORMAT_9BIT_666
#   2: DPI_OUTPUT_FORMAT_16BIT_565_CFG1
#   3: DPI_OUTPUT_FORMAT_16BIT_565_CFG2
#   4: DPI_OUTPUT_FORMAT_16BIT_565_CFG3
#   5: DPI_OUTPUT_FORMAT_18BIT_666_CFG1
#   6: DPI_OUTPUT_FORMAT_18BIT_666_CFG2
#   7: DPI_OUTPUT_FORMAT_24BIT_888
#
# rgb_order:
#   1: DPI_RGB_ORDER_RGB
#   2: DPI_RGB_ORDER_BGR
#   3: DPI_RGB_ORDER_GRB
#   4: DPI_RGB_ORDER_BRG
#
# output_enable_mode:
#   0: DPI_OUTPUT_ENABLE_MODE_DATA_VALID
#   1: DPI_OUTPUT_ENABLE_MODE_COMBINED_SYNCS
#
# invert_pixel_clock:
#   0: RGB Data changes on rising edge and is stable at falling edge
#   1: RGB Data changes on falling edge and is stable at rising edge
#
# hsync polarity: 
#   0: default for HDMI mode
#   1: inverted
#
# vsync polarity:
#   0: default for HDMI mode
#   1: inverted
#
# output_enable_polarity:
#   0: default for HDMI mode
#   1: inverted
#
# hsync phase:
#   0: rising edge
#   1: falling edge
#
# vsync phase:
#   0: rising edge
#   1: falling edge
#
# output_enable phase:
#   0: rising edge
#   1: falling edge
# ---------------------------------------------
dpi_output_format=458773


# ---------------------------------------------
# HDMI timing definitions
#https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=24679
# ---------------------------------------------
# hdmi_timings= <h_active_pixels>
#		  LCD module horizontal resolution
#
#               <h_sync_polarity>
# 		  0: active low
#		  1: active high
#
#               <h_front_porch> 
#		<h_sync_pulse>
#		<h_back_porch>
#		<v_active_lines>
#		  LCD module vertical resolution
#
#		<v_sync_polarity>
# 		  0: active low
#		  1: active high
#
#		<v_front_porch>
#		<v_sync_pulse>
#		<v_back_porch>
#
#		<v_sync_offset_a>
#		<v_sync_offset_b>
#		<pixel_rep>
#
#		<frame_rate>
#		  screen refrech rate (50/60Hz supported only!)#
#
#		<interlaced>
#
#		<pixel_freq>
#		  calculates as: <h_active_pixels> * <v_active_lines> * <frame_rate>
#
#		<aspect_ratio>
#		  HDMI_ASPECT_4_3 = 1
#		  HDMI_ASPECT_14_9 = 2
#		  HDMI_ASPECT_16_9 = 3
#		  HDMI_ASPECT_5_4 = 4
#		  HDMI_ASPECT_16_10 = 5
#		  HDMI_ASPECT_15_9 = 6
#		  HDMI_ASPECT_21_9 = 7
#		  HDMI_ASPECT_64_27 = 8
# ---------------------------------------------
#hdmi_timing for LQ084V1DG43 configuration notes
#h_active_pixels = 640
#h_sync_polarity = 1
#h_front_porch = 2
#h_sync_pulse = 5 
#h_back_porch = 88
#v_active_lines = 480
#v_sync_polarity = 0
#v_front_porch = 13
#v_sync_pulse = 1
#v_back_porch = 34
#v_sync_offset_a = 0
#v_sync_offset_b = 0
#pixel_rep = 0
#frame_rate = 60
#interlaces = 0
#pixel_freq = 640 * 480 * 60 = 18432000
#aspect_ratio = 1
# ---------------------------------------------
hdmi_timings=640 1 2 5 88 480 0 13 1 34 0 0 0 60 0 18432000 1

# Uncomment this to enable the lirc-rpi module
#dtoverlay=lirc-rpi

# Additional overlays and parameters are documented /boot/overlays/README

and here is what it Looks like:

Sharp 8.4in LQ084V1DG43

small1.jpg (50.65 KiB) Viewed 11914 times

small2.jpg (47.15 KiB) Viewed 11914 times

Sorry to say, but: no HDMI output when using this config.txt

[tvjon]

"Sorry to say, but: no HDMI output when using this config.txt "

Your HDMI output should work just fine for egles app's & omxplayer. It certainly does for me.

Try:

omxplayer --display 5 some-mpeg4-or-h264-movie.mp4