Beeb emulator on Raspberry Pi

[noggin]

My cheap TV is cropping the left of the display a bit - when it's fed VGA, and my cheap VGA2HDMI converter doesn't seem to want to play ball over HDMI into that TV. But this is AMAZING!

Always worth giving auto-adjust (or equivalent) a go. this should be a pretty standard-ish 1280x1024 timing (640x256 is a blessed beeb resolution for beeb!). (perhaps your VGA->HDMI doesn't go that high; worth trying some other pico-playground video demos if you have them)

Yep - gave Auto Adjust a go and still had the issue. I think it's a problem with the TV - as I can't get it to switch into 4:3 mode at 1280x1024 50Hz - though 50Hz resolutions are out-of-spec for 'pure VGA' I guess (which has always been deeply dull in European broadcast video circles when it comes to VGA)

Have another VGA->HDMI adaptor on its way from Amazon - will see if that does better. Fewer and fewer displays have analogue VGA in these days

[hoglet]

Does it not interfere with the video (it certainly caused a pause during the bee-boop of startup for me as TinyUSB slept in an IRQ handler, but maybe i'm just on back-level TinyUSB!) Can you let me know the git hashes of things you have pico-sdk, pico-sdk/lib/tinyusb and pico-extras?

Yes, the presence of the USB keyboard does introduce a pause into the boo-bip, so you end up with a boo-boo-bip. I've also noticed some very minor video issues that looks like very occasional missing scanlines. But it's hard to tell if these relate to the USB keyboard or not.

Library versions:

Code: Select all

pico-sdk:
    2d5789eca89658a7f0a01e2d6010c0f254605d72

pico-sdk/lib/tinyusb
    e0aa405d19e35dbf58cf502b8106455c1a3c2a5c

pico-extras:
    89b8071d2a99e1af25b01c6cb0380ae0216053ca
    
arm-none-eabi-gcc:
    gcc version 7.3.1 20180622 (release) [ARM/embedded-7-branch revision 261907] (GNU Tools for Arm Embedded Processors 7-2018-q3-update) 

Dave

[fordp]

This looks great. I hope to get round to trying it at some point.

Just one comment this thread starts talking about Linux Pi's and then switches to Pico part way through would it not make sense to split this thread?

[hoglet]

Just one comment this thread starts talking about Linux Pi's and then switches to Pico part way through would it not make sense to split this thread?

Graham's version supports both the Pico and the Pi 2/3/4 I believe.

Dave

[kilog]

My cheap TV is cropping the left of the display a bit - when it's fed VGA, and my cheap VGA2HDMI converter doesn't seem to want to play ball over HDMI into that TV. But this is AMAZING!

Always worth giving auto-adjust (or equivalent) a go. this should be a pretty standard-ish 1280x1024 timing (640x256 is a blessed beeb resolution for beeb!). (perhaps your VGA->HDMI doesn't go that high; worth trying some other pico-playground video demos if you have them)

Yep - gave Auto Adjust a go and still had the issue. I think it's a problem with the TV - as I can't get it to switch into 4:3 mode at 1280x1024 50Hz - though 50Hz resolutions are out-of-spec for 'pure VGA' I guess (which has always been deeply dull in European broadcast video circles when it comes to VGA)

Have another VGA->HDMI adaptor on its way from Amazon - will see if that does better. Fewer and fewer displays have analogue VGA in these days

yes, i remembered after I wrote it that it is 50hz! it is I think VESA CVT valid, but that is not the same as "standard" by any means

[kilog]

Does it not interfere with the video (it certainly caused a pause during the bee-boop of startup for me as TinyUSB slept in an IRQ handler, but maybe i'm just on back-level TinyUSB!) Can you let me know the git hashes of things you have pico-sdk, pico-sdk/lib/tinyusb and pico-extras?

Yes, the presence of the USB keyboard does introduce a pause into the boo-bip, so you end up with a boo-boo-bip. I've also noticed some very minor video issues that looks like very occasional missing scanlines. But it's hard to tell if these relate to the USB keyboard or not.

Library versions:

Code: Select all

pico-sdk:
    2d5789eca89658a7f0a01e2d6010c0f254605d72

pico-sdk/lib/tinyusb
    e0aa405d19e35dbf58cf502b8106455c1a3c2a5c

pico-extras:
    89b8071d2a99e1af25b01c6cb0380ae0216053ca
    
arm-none-eabi-gcc:
    gcc version 7.3.1 20180622 (release) [ARM/embedded-7-branch revision 261907] (GNU Tools for Arm Embedded Processors 7-2018-q3-update) 

Dave

yeah i think the missing scanlines was the issue with the USB I htink (there are none of those without)... i need to either do my own USB host or force TinyUSB to not do stuff outside of vsync (which actually may be easy, if I just turn of IRQs in between!) - there are rare losses of frame sync for a frame even without USB... you may notice these if you leave it sitting after boot for a while.

P.S. thanks for the git hashes; i'll give that build.
P.S>

[Alyinsanfran]

I’m getting a 400 (my first Pi) purely because of this emulator. I’ve wanted a Beeb ever since my NZ high school had them (mid 80s), but outside of the UK they’re extremely rare, let alone a good ‘un - especially since I moved to the States. I’m experienced with emulators (Mame on NT ftw), but this is the first one to excite me in years. Imho the Beeb was the absolute pinnacle of 8 bit home computing.

[noggin]

Always worth giving auto-adjust (or equivalent) a go. this should be a pretty standard-ish 1280x1024 timing (640x256 is a blessed beeb resolution for beeb!). (perhaps your VGA->HDMI doesn't go that high; worth trying some other pico-playground video demos if you have them)

Yep - gave Auto Adjust a go and still had the issue. I think it's a problem with the TV - as I can't get it to switch into 4:3 mode at 1280x1024 50Hz - though 50Hz resolutions are out-of-spec for 'pure VGA' I guess (which has always been deeply dull in European broadcast video circles when it comes to VGA)

Have another VGA->HDMI adaptor on its way from Amazon - will see if that does better. Fewer and fewer displays have analogue VGA in these days

yes, i remembered after I wrote it that it is 50hz! it is I think VESA CVT valid, but that is not the same as "standard" by any means

I've now had partial success with a Vention cheap VGA->HDMI adaptor - my Sony UHD TV reports something like 1152 x 864 @ 50Hz with a 4:3 light-grey window in a 16:9 frame. The light grey window is the VGA active video and shows about 21 lines of MODE 7, and a bit more of MODE 0. A lot better than a blank screen

The image is shifted to the right, and the bottom of frame is cropped - but it's better than the left of frame being cropped (which is what my cheap 23" Chinese HDTV did when fed VGA directly). Not sure if the lifted blacks are because of a clamp issue, a 16-235 vs 1-254/0-255 issue or something else...

I've bought a bunch of others - will report back which are the best. (All of them capture audio and insert it into the HDMI signal - which is useful)

[kilog]

Yeah, i have had success with this https://smile.amazon.com/gp/product/B01N53IESF, though it may be more of a TV issue as the timing is likely just passed thru

Works fine with my LG OLED, and all the monitors i've tried, but yes it would be great to get an understanding of which do and don't work; it is of course possible to tweak the timings slightly if need em.

[anightin]

Awesome achievement for showing off the Pico.

I thought I'd give this a quick try so assembled the pico on the demo board and dropped in @hoglet's master.uf2.

I transferred the master.uf2 in mass storage mode on the Pico and after it loaded it unmounted and reboot as expected.

I'm powering via the demo board and have a USB keyboard on the Pico.

The video output doesn't seem to be recognised by my Technika TV unit with VGA input. I plugged in my OSSC for it to have a look at the output and got the following:

I'll try it on other screens, but just wanted to check first if there was a fundamental step I'm missing?


Many thanks

[hoglet]

I'll try it on other screens, but just wanted to check first if there was a fundamental step I'm missing?

You do need a TV/monitor that will support 1280x1024 @ 50Hz over VGA - many don't.

[noggin]

I've now tested 5 VGA->HDMI converters - they fall into three camps :

1. Don't work.

https://www.amazon.co.uk/gp/product/B01 ... UTF8&psc=1 (I bought this model a couple of years ago - so it may have since changed - but it didn't work on any HDMI display I had - no apparent output at all. It's 4 years old - it may be dead !)

2. Partially work - but you get a grey background rather than black, and an incorrectly positioned screen with a lot of padding at the top of frame, a bit of a right shift, and a lot of crop at the bottom.

Reported output res on TV 1152x864 @ 50Hz
https://www.amazon.co.uk/gp/product/B07 ... UTF8&psc=1
https://www.amazon.co.uk/gp/product/B07 ... UTF8&psc=1

3. Fully work - black background, no apparent crop as far as I can tell - maybe the very top line, and maybe a bit of padding at the bottom of frame. It's all quite underscanned (don't know if that's my TV) - but a LOT better than 2. Once or twice I've had a missing left column or two but removing and re-inserting the VGA adaptor fixed that (I guess it does a resync/analyse)

Reported output res on TV 1280x1020 @ 50Hz
https://www.amazon.co.uk/gp/product/B08 ... UTF8&psc=1
https://www.amazon.co.uk/gp/product/B07 ... UTF8&psc=1

My HD Fury Vertex HDMI analyser recognises them as 50.010Hz and either 78 or 90MHz clock - but not as valid HDMI formats (though who knows what the VGA adaptors are doing...)

[anightin]

I'll try it on other screens, but just wanted to check first if there was a fundamental step I'm missing?

You do need a TV/monitor that will support 1280x1024 @ 50Hz over VGA - many don't.

Got it thanks @Hoglet, glad my main workshop monitor has this capability

[anightin]

I've now tested 5 VGA->HDMI converters - they fall into three camps :

3. Fully work - black background, no apparent crop as far as I can tell - maybe the very top line, and maybe a bit of padding at the bottom of frame. It's all quite underscanned (don't know if that's my TV) - but a LOT better than 2. Once or twice I've had a missing left column or two but removing and re-inserting the VGA adaptor fixed that (I guess it does a resync/analyse)

Reported output res on TV 1280x1020 @ 50Hz
https://www.amazon.co.uk/gp/product/B08 ... UTF8&psc=1
https://www.amazon.co.uk/gp/product/B07 ... UTF8&psc=1

My HD Fury Vertex HDMI analyser recognises them as 50.010Hz and either 78 or 90MHz clock - but not as valid HDMI formats (though who knows what the VGA adaptors are doing...)

Thanks @Noggin, that save's a lot of trial and error

[lushprojects]

Thanks for the work on this. Fantastic you can emulate a beeb on the Pi Pico.

I don't know if you want pull requests, but I have sent one on Github as I thought it would be useful to document the requirements for extra hardware to get the VGA out. It might be worth explaining any other hardware breakout the project uses or depends on too.

[kilog]

Yeah, i do take PRs ... i guess i have been super lucky with the monitors i've tried. I wonder if minor tweaks will help. Sadly 5/6 frame pull down at 60Hz isn't possible without video RAM, so the emu would have to run at 60Hz to do a 60Hz mode, but maybe some monitors would like that better (but of course that needs the code to run 20% faster which may need another clock bump)

[hoglet]

Did you ever get the Pico emulator working with HDMI output?

I think 50Hz over HDMI is far more widely supported than 50Hz over VGA.

[noggin]

Did you ever get the Pico emulator working with HDMI output?

I think 50Hz over HDMI is far more widely supported than 50Hz over VGA.

Yes - I think technically no 'real' VGA signal has been as low a vertical refresh rate as 50Hz - thought lots of 50Hz capable displays will accept such a signal.

50Hz is a valid refresh rate for 576i composite, and for 576i, 576p, 720p, 1080i and 1080p (*) for component analogue and HDMI. HDMI uses pixel repetition for 576i to get the pixel clock rate high enough (I think it runs at 1440 pairs of duplicate samples to double the pixel clock that would otherwise be required for 720x576 at 25Hz frame rate / 720 x 288 at 50Hz field rate)

AIUI the 576i HDMI modes were added to the spec quite late on, and at one point 576p was the lowest 50Hz resolution supported, which may be why Sky HD boxes don't output 576i over HDMI.

Analogue RGB with H+V composite/mixed syncs at 15.625kHz / 50Hz (i.e. regular "PAL" timing) would potentially be very useful - as that would be SCART compatible ?

[kilog]

Yes - I think technically no 'real' VGA signal has been as low a vertical refresh rate as 50Hz - thought lots of 50Hz capable displays will accept such a signal.

50Hz is a valid refresh rate for 576i composite, and for 576i, 576p, 720p, 1080i and 1080p (*) for component analogue and HDMI. HDMI uses pixel repetition for 576i to get the pixel clock rate high enough (I think it runs at 1440 pairs of duplicate samples to double the pixel clock that would otherwise be required for 720x576 at 25Hz frame rate / 720 x 288 at 50Hz field rate)

AIUI the 576i HDMI modes were added to the spec quite late on, and at one point 576p was the lowest 50Hz resolution supported, which may be why Sky HD boxes don't output 576i over HDMI.

Analogue RGB with H+V composite/mixed syncs at 15.625kHz / 50Hz (i.e. regular "PAL" timing) would potentially be very useful - as that would be SCART compatible ?

PAL should be possible, i just never tried it because monitors definitely don't like that - as I say i'd like to try generating a CUB compatible signal (using the actual CRTC timings!)

Where did you find that info on valid 50hz modes?... 1920x1080x50 would probably be doable. with 3x2 pixels, just gives you a few more lines! Do you have timings handy; i'll have a search on line too... how sucessful we are really depending on the pixel clock

generally i just guess on the hsync/vsync polarities, so mine might be wrong for the existing 1280x1024

[kilog]

note it is a bit bizarre, but I wonder if the US monitors like this better for some reason!?

I have found timing for 1920x1080x50, and that would require a 297Mhz clock vs 270, so should probably still work

[kilog]

Thanks for the suggestion on 1080p 50

I have pushed a new commit which adds two new binaries to the pico build beeb_1080p and master_1080p

These seem to work nicely for me (bear in mind tho now that the pico is overclocked to 297Mhz - which I think will still work on all)

I suspect that a widescreen monitor may now recognize this as a "widescreen" mode so it may be switched, but i believe I can probably add an in game menu option to squish to 2/3 of the width which would be quite cool!

[GreyAreaUK]

Just wanted to say a huge 'thank you' to everyone involved in this.

May I also ask some (undoubtedly stupid) questions? Namely: Is there a version of this that I can run on a Pi2 without X11? Failing that, can I run them fullscreen? My apologies but Linux/X11 are a little outside of my normal areas and I'm very much a newbie in them!

Many thanks.

[kilog]

There isn't currently a version which runs without X11, but it is certainly possible... I'm not sure i'm gonna get to it any time soon, but maybe someone else will. You can make the window bigger!

[kilog]

Thanks for the suggestion on 1080p 50

I have pushed a new commit which adds two new binaries to the pico build beeb_1080p and master_1080p

These seem to work nicely for me (bear in mind tho now that the pico is overclocked to 297Mhz - which I think will still work on all)

I suspect that a widescreen monitor may now recognize this as a "widescreen" mode so it may be switched, but i believe I can probably add an in game menu option to squish to 2/3 of the width which would be quite cool!

Note that this discussion is now continued in a separate RP2040 thread (though I did add said menu option!)

[GreyAreaUK]

There isn't currently a version which runs without X11, but it is certainly possible... I'm not sure i'm gonna get to it any time soon, but maybe someone else will. You can make the window bigger!

Thanks for the reply - just wanted to be sure I wasn’t missing something obvious!

[kilog]

BTW emu runs great on Pi Zero 2 W

[scruss]

It's a nice little machine, the Zero 2 W. I've had one on my bench at work since the Approved Reseller's event and it was extremely hard to keep quiet about it.

[noggin]

Yes - I think technically no 'real' VGA signal has been as low a vertical refresh rate as 50Hz - thought lots of 50Hz capable displays will accept such a signal.

50Hz is a valid refresh rate for 576i composite, and for 576i, 576p, 720p, 1080i and 1080p (*) for component analogue and HDMI. HDMI uses pixel repetition for 576i to get the pixel clock rate high enough (I think it runs at 1440 pairs of duplicate samples to double the pixel clock that would otherwise be required for 720x576 at 25Hz frame rate / 720 x 288 at 50Hz field rate)

AIUI the 576i HDMI modes were added to the spec quite late on, and at one point 576p was the lowest 50Hz resolution supported, which may be why Sky HD boxes don't output 576i over HDMI.

Analogue RGB with H+V composite/mixed syncs at 15.625kHz / 50Hz (i.e. regular "PAL" timing) would potentially be very useful - as that would be SCART compatible ?

PAL should be possible, i just never tried it because monitors definitely don't like that - as I say i'd like to try generating a CUB compatible signal (using the actual CRTC timings!)

Where did you find that info on valid 50hz modes?... 1920x1080x50 would probably be doable. with 3x2 pixels, just gives you a few more lines! Do you have timings handy; i'll have a search on line too... how sucessful we are really depending on the pixel clock

generally i just guess on the hsync/vsync polarities, so mine might be wrong for the existing 1280x1024

Sorry - didn't ever see this question. re : "Where did you find that info on valid 50hz modes?"

Analogue VGA didn't ever go down as low as 50Hz vertical refresh, and the HDMI standards are part of the EIA/CEA 861 spec.

https://en.wikipedia.org/wiki/Extended_ ... #CEA-861-E

720x576i25 and 720x480i29.97 have clock rates that are too low for HDMI - so they use 1440x576 or 1440x480 with sample/pixel duplication/replication to get the rate high enough.

[hatman72]

Here's an article from the Raspberry Pi blog detailing how to emulate a beeb on a Raspberry Pi 400 using the B-Em emulator:

https://www.raspberrypi.com/news/emulat ... ry-pi-400/

[scruss]

Here's an article from the Raspberry Pi blog detailing how to emulate a beeb on a Raspberry Pi 400 using the B-Em emulator:

https://www.raspberrypi.com/news/emulat ... ry-pi-400/

That's a neat, if slightly involved, way of building it. This is simpler: B-Em - Page 21 - stardot.org.uk