BRT Community

Ok, this got lost in the forums update, so I am trying to re-post.

Quote
On the programmers guide point, this is currently going through the final review stages and we hope to have it released shortly.

Hmm, how do I put this in writing? Just remember that I am not in a bad mood over here.
I has been over three weeks now with me checking every day if there had been an update.

And I was promised answers to my questions but this thread practically went on as a blog with close to no answers.
In the meantime you use for example the undocumented host command E7 in your own code - which I had not seen when it was put in 5 months ago since I try to barely look at your code, following the mantra that if it is not documented, it does not exist.
This is a tad bit frustrating.

Well now, there still is an unfortunate lack of available ready-to-use EVE5 display modules, none to be precise and I wonder why that is.

Anyways, here is something for the FAQs, maybe:

Can I use the dual channel LVDS output of the BT820B with two single channel LVDS displays?

No, first of all the output in dual-channel mode is interleaved, so one channel is sending the even pixels, the other channel is sending the odd pixels.
Then there is only one clock setting and one set of REG_SO_ registers, so even if the scanout engine could be convinced to output non-interleaved, it could only output the same information in parallel to two LVDS channels, so the same image on two identicle displays.

Is this an accurate assesment?
There is more, but this is probably enough on the question of using two displays with the BT820B.

Unfortunately I can not repost directly, I am not making backups of the posts here. :-)
And I checked the wayback machine, no backup there either.

Well, now we know.

Well, let's try. :-)

Do you have a chance to restore the couple of posts that got lost?

Hello, it has been a few days since there was a rollback on the forum and nothing new got posted since then.
What happened?

What worked best for me across several different MCUs and ready-to-use FT81x/BT81x modules are 74LVC2G17 / 74VHC1G12 buffers and 56R series resistors.

The slew rate / drive strength settings are a bit counter intuitive.
ST for example has "Maximum output speed" settings for the STM32 with levels "Low" / "Medium" / "High" and "Very High".
But using "Very High" is not necessarily the correct idea.
Ideally you match the output to your transmission line impedance.

Analog voodoo in digital transmissions. :-)

For very long I had the luxury of getting away with ignoring the issue.
First my controllers were on the slower side and did not have any settings while driving the lines rather strong,
then I had an issue with a controller having too weak outputs at 3.3V, so I added external buffers as drivers.

Next I learned that my library was not playing well with the Teensy 4 which uses a RT1062, the usuable SPI clock was surprisingly low.
As the Teensy 4 is typically used with Arduino, the settings are made by the classes.
And when I figured out how to change the settings in order to configure for a higher speed, I learned that by default the pins
already were configured for the highest setting.
Using a lower setting worked better - or raising the series resistance.

Please attach logfile from your logic-analyzer, there really is not much to see in these images.
Not that I am expecting to see anything at 12MHz, but there is not really much to analyze with these images.

Any ETA on an updated BT82x programming guide?

A few answers to the more crucial questions I posted would be very nice beforehand.
Like how REG_LVDSTX_PLLCFG actually works - if the guide is wrong there and I am not using the register incorrectly...


And I have a new question.
Is there a way to check if rendering of a display list is done?
Well yes, I could read REG_RE_RENDERS and check for a change.
But this takes a bit of caution and requires to not into a deadlock.
Or I guess using CMD_GRAPHICSFINISH could work, reading REG_CMDB_SPACE after this should indicate that the co-processor is waiting for the render engine to finish.
Hmm, sounds like a plan, I maybe should always end the BT82x display list with CMD_GRAPHICSFINISH and not send a new display list when the co-processor is still busy.

Well yes, there might be other things to do for the co-processor while the render-engine is busy, like loading assets or using CMD_TEXTDIM, in that case ending the display-list with CMD_GRAPHICSFINISH might be a bit inefficent, perhaps, especially when the render engine needs a bit more time than usual.

Just a thought, what is your SPI clock and have you tried to reduce it while reading?

In my experience, writing to EVE works a whole lot faster reliably than reading does.
And then there is driving the lines thru at least two connections of a FFC, depending on the layout,
the host mcu and the settings for the pins, SPI_CLK might not be looking so good and there might be reflections.

Time for some torture-testing of the BT820. :-)

The attached image shows this code:


        int16_t xc0 = 0;
        int16_t yc0 = 0;
        uint16_t length = 3;
        static uint16_t increase = 0;
        uint32_t colors[] = {RED, ORANGE, GREEN, BLUE, YELLOW, MAGENTA, PURPLE, BLACK, 0xc0c0c0, BLUE_1};

        for(uint8_t arms = 0; arms < 12; arms++)
        {
            EVE_color_rgb(colors[arms]);
            EVE_begin(EVE_LINE_STRIP);
            for(uint8_t steps = 0; steps < 135; steps++)
            {
                EVE_polar_cartesian(length*steps, arms*30+steps*increase, &xc0, &yc0);
                EVE_vertex2f(xc0 + 450, yc0 + 320);
            }
            EVE_end();
        }

        static uint8_t delay = 0;

        delay ++;

        if(delay > 2)
        {
            delay = 0;
            increase += 3;
        }


12 Linestrips with 135 segments each, 6916 bytes in the SPI buffe, a display-list of >8100 bytes, takes 1.3ms to preprare the buffer.
And this runs continously now, changing constantly.

All I noticed was that it started to flicker when I increased the "steps" in the loop.
Not for every value of "increase" though.
The flickering goes away when I decrease the maximum "steps" or increase the time between display-list updates.
Right now I am running this as posted and refresh the display list every 75ms, so 13 changes per second.
So this put the render-engine into stress-mode, sort of.

Nice, this stupid level of useless complexity should be way beyond what a normal application can put out to render. 

Some might have noticed it already, I uploaded a new library on Github: https://github.com/RudolphRiedel/EmbeddedVideoEngine
I had the idea of renaming my library for a while, "FT800-FT813" was just wrong for a while now.
However, renaming seemed to be a bit disruptive, so I created a new repository for V6 of my library and the name should be future-proof now. :-)
I was already using the name for a while now in the library.json for PlatformIO.

Yesterday I tested the Arduino example, made sure it compiles for all tagets (although a few are non functional like the one for BBC Microbit.
And then I tested ESP32-S2, Arduno UNO V3, Teensy 4.1, Raspberry Pi Pico and Metro M4 with both a RVT50H (BT817) and the VM820C.

Right now I have the VM820C with the 7" 1024x600 TFT up and running with an ATSAME51 after a fix to the DMA code, and I already checked it with a BT817.
As usual, no warnings with -Wall -Wextra -pedantic.

Before I was using a STM32F407, so most targets are covered by now, at least are compiling or actually are tested.

While the lib is feature complete for the BT820, this is not finished.
There are still a couple of things missing like configuring the memory size for the BT820, the LVDS output clock is merely working by chance now, Audio does not seem to be working at all, video input is unexplored...

Unfortunately there are no modules for sale with a BT820, as far as I know. And only one was anounced.

I also learned again that sourcing LCDs is still a major pain, these things are really not commodities, speaking of course for not buying in bulk from a company account, trying to aquire single units.

I implemented CMD_LOADWAV and in order to test it I enable audio in BOOTCFG.
The screen stays black though.

The host command is correct, it changes from 0xff 0xe8 0xc0 0x00 0x00 to 0xff 0xe8 0xe0 0x00 0x00.
Things look normal on the logic analyzer, "only" the screen stays black.

I am not writing to any of the audio registers, including not using CMD_LOADWAV.
I even moved the buffers for the swapchains.

Is it possible that the audio engine is messing with the clock tree?

I implemented a couple more commands and got to CMD_WATCHDOG.

Quote
The watchdog command enables the watchdog timer and sets the watchdog reset intervals in clocks.
The watchdog flag in REG_BOOT_CFG register must be set.

C prototype
void cmd_watchdog ( uint32_t init_val );

Command layout
+0 CMD_WATCHDOG(0xFFFF FF83)
+4 init_val

Parameters
init_val
Watchdog timeout initialization value, in clocks. Must be a sensible value to prevent
watchdog being triggered prematurely.

Examples
To set the watchdog timeout every 72000000 clocks, which is 1 second on a 72 MHz system:
cmd_watchdog(72000000);

Quote
Adds watchdog timer to facilitate automatic correction.

Quote
The watchdog timer uses a 32-bit counter and is driven by the system clock. Hence, at default system
clock of 72 MHz, the maximum timeout period supported is 59.6s.
The watchdog timer begins and resets as it counts down from a user-defined initial value. Upon reaching
a count value of zero, the watchdog timer generates a system reset. The timer needs to be periodically
reset to the initial value to prevent the system reset from happening.
Refer to BRT_AN_086 BT82X Series Programming Guide for details on how to program the Watchdog
Timer using cmd_watchdog

That is practically all if it.
So yes, the watchdog system needs to be enabled during boot.
And it does a system reset - whatever "automatic correction" this is good for.
Then there is CMD_WATCHDOG which is documented to enable the watchdog and configure the timeout.
But there is no command like CMD_TRIGGER_WATCHDOG, so CMD_WATCHDOG is resetting the timer?

And if CMD_WATCHDOG really is the only command, does a CMD_WATCHDOG(0) disable the watchdog?

What safety requirements are covered by this?
If the EVE chip would crash hard, and I never encountered this, would the watchdog timer really not be affected?
And how would a reset help in this scenario? The host controller had to detect either way that the EVE chip is not answering anymore.
Ok, different scenario, the host controller crashes, how would resetting the EVE chip help? The host controller would still be dead.
So when the watchdog is not triggered by CMD_WATCHDOG, the screen goes dark?

What am I missing here?
If the EVE chip would be able to reset the host controller, that would be different, that would make the EVE chip an external watchdog controller and that could  be viewed as positive for the system safety.
But I would use a window-watchdog with challenge-response for such a task, preferably in a SBC.

Another day, another screen of progress. :-)

I just added CMD_LOADASSET and tried it with two fonts converted with EAB 3.0.
Loading from SD card is really nice.

I am wondering what is driving up the display-list so much.
EVE_cmd_cgradient(EVE_EDGE_ZERO, 300, 200, 200, 200, WHITE, PURPLE); - 140 bytes
EVE_cmd_arc(400, 300, 100, 110, 0, 16384); - 144 bytes
debug-output of 8 hex-numbers - 736 bytes

Ok then, most of it is for all the text.

QuoteOne way to check is to perform a cmd_fssize.  Directories will return -1 for the size.

Well, yes and no, technically. :-)
The size is documented to be a uint32_t.

And I got a couple of steps further along now, my test code is using CMD_FSSOURCE, CMD_LOADIMAGE with OPT_FS and CMD_GETIMAGE
to load one of the files returned by CMD_FSDIR and then display it.
I also found OPT_TRUECOLOR during this.

I am trying out the SD card functions now and just successfully used CMD_FSDIR.

CMD_FSDIR "only" returns a bunch of names.
How can I find out which of these names are directories?

Edit: I implemented CMD_FSSIZE and the number returned for directories is 0xffffffff.
Well, yes, that matches the description of CMD_FSSIZE, that entry is not a file, so no file of that name was found.
And consequently CMD_FSREAD and CMD_FSSOURCE return 2 on folders for file-not-found.

So when the name is returned by CMD_FSDIR and CMD_FSSOURCE returns 2, then it is a folder.