DMG/Pocket video capture with Arduino or Teensy? (Page 6 of 16)

Nope, that's not possible. You see the data signals come when one clock pulse is still high. Which means if we're reading data on CLOCK's falling edge (an this is exactly what we're doing) the bits are already there.  Clock and data signals are kind of overlapping if you plot them. Thus it's guaranteed that data is read.

24 cycles in not much really. For example a 1 line of C code can compile to 10 commands and each command may be several bytes long.

I checked with Craig from Flashing LEDs and he confirmed this theory and suggested to use external SPI chips. I need to dig in this direction. But so far to do this really neatly probably an FPGA is needed. I love the idea of FPGA but the opportunity of learning absolutely counter intuitive Verilog or VHDL hurts me before I even started.

Just what I need ,but way to complex for me :-/

I still think it is worth trying friendofmegaman's code without the Serial.write slowing down the interrupt to see what difference it makes, as I wrote earlier:

http://chipmusic.org/forums/post/206984/#p206984

Also, using low-level AVR port manipulation commands (PORT, PIN, DDR) isn't necessarily going to speed things up on a Teensy 3.x (ARM) because they just end up going through another level of AVR to ARM emulation:

http://github.com/PaulStoffregen/cores/ … mulation.h

http://forum.pjrc.com/threads/17532

You need to actually use ARM low level commands! Grab the MK20DX256 manual here:

http://www.pjrc.com/teensy/datasheets.html

and check out Chapter 11 - Port control and interrupts (PORT) and Chapter 49 - General-Purpose Input/Output (GPIO)

The code I posted earlier (p. 3), which only increments a variable in the ISR (serial is done in the work loop), demonstrates the same problem.  I also wrote an even simpler version which sends a pulse on an output pin when the clock ISR is called.  I compared the output signal with the clock signal using a DSO (which may not be entirely reliable for this application) and found that the ISR was not being triggered for most of the clock pulses.  I can post this code if you are interested.

The more I read about the Teensy 3.x, the more I feel that it is a poorly thought out development system, with a poor library which makes it unsuitable for this application, and likely for many of the tasks which the Freescale chip would be capable of.  Thankfully, it seems that most (if not all) of the issues lie with the libraries, rather than the board itself, and so can probably be avoided if we do not use the TeensyDuino libraries.

Knowing what I know now, I would have likely not chosen a Teensy for this project, and would recommend to anyone else wishing to get involved and buy hardware to consider other options (and perhaps suggest them here), rather than jumping in and buying a Teensy.  Nonetheless, I have a Teensy now, and so will persist with it and see how far we can get.  Also, the Teensy retains the advantage of being reasonably cheap.

Here is another thought, though: How feasible is it to forget the Teensy and simply use a logic analyser to capture the data, and process it on the PC using code not unlike friendofmegaman's original version (i.e, poll the signals)?  Craig of Flashing LEDs has more or less done this, but can it be done in realtime?

Last edited by rvan (Apr 26, 2014 7:48 am)

I would be interested, yes.

Again, the code you posted earlier is also doing a Serial.write on every HSYNC, and I can't help but think that is eating up a lot of cycles and again would suggest to maybe try storing those values in an array or something instead, and then Serial.write them out once you've collected a certain amount to see if that has any effect on the count?

If this was directed at me, the answer is an unequivocal yes.  I am happy to share any of my work on this.  I don't, however, currently own a logic analyser.  I am planning on possibly buying an inexpensive one from China, but this would be a while in arriving.  First, I will do some research into APIs, as we would have to be able to access the data from the logic analyser directly.

Here it is:

//Author: rvan
/* A simple program to output pulses when a clock signal is received.  Pin 13
   is the LED pin, but we also attach a DSO probe here.  Currently this program
   DOES NOT produce the intended output, presumably because the ISR returns too
   slowly.
 */

#include <WProgram.h>

#define CLOCK_PIN 23
#define OUT_PIN 13

volatile bool have_clock = false;

unsigned int i;

void clock_ISR() {
    have_clock = true;
}

int main() {
    pinMode(CLOCK_PIN, INPUT);
    pinMode(OUT_PIN, OUTPUT);
    attachInterrupt(CLOCK_PIN, clock_ISR, RISING);

    for(;;) {
        if(have_clock) {
            digitalWrite(OUT_PIN, HIGH);
            i++; i--; i++; i--; //This creates a very short delay.
            digitalWrite(OUT_PIN, LOW);
            have_clock = false;
        }
    }
}

Ah, I see what you mean; I thought you were simply talking about doing a serial write within the ISR or not.  I will try this out tonight.

Last edited by rvan (Apr 26, 2014 8:35 am)

Does this mean that is is not possible to capture a continued data stream with a typical logic analyser?

This would probably require underclocking the Game Boy (unless using a faster microcontroller).  Obviously, this isn't ideal.  However, if the Game Boy is driven by a clock signal synthesised by the microcontroller, then pixels will arrive at a predictable cycle relative to the work loop, and can be read directly, with no need for polling or interrupts.  Has anyone (nitro, most likely) tried single-stepping the Game Boy's processor?  Being able to do so would aid in designing a solution using this approach.

I think the option of using SPI (probably dual SPI buses), as per Craig, is still feasible.  I also raised the idea of DMA on the Teensy, but I don't know whether this is feasible or not.  Here is a thread on the PJRC fora which might be relevant: http://forum.pjrc.com/threads/999-ARM-assember-code

For those interested, I have updated my post on the first page with a link to a thread on snesy's Gameboy Classic VGA-Adapter, in German.

Last edited by rvan (Apr 26, 2014 8:56 am)