fractal_demo -

Users » robyounger » Code » fractal_demo

Rob Younger / Mbed 2 deprecated fractal_demo

composite.cpp@0:fb93ebe5f84f, 2009-11-15 (annotated)

Committer:: robyounger
Date:: Sun Nov 15 15:52:54 2009 +0000
Revision:: 0:fb93ebe5f84f

Who changed what in which revision?

User	Revision	Line number	New contents of line
robyounger	0:fb93ebe5f84f	1	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	2	// Software generation of a grayscale composite TV signal //
robyounger	0:fb93ebe5f84f	3	// Puts a 105x128 grayscale fractal zoom onscreen (slow!) //
robyounger	0:fb93ebe5f84f	4	// //
robyounger	0:fb93ebe5f84f	5	// Hacked together, (ab)uses the LPC1768 DAC output (p18) //
robyounger	0:fb93ebe5f84f	6	// with some shifty looking timing sensitive code //
robyounger	0:fb93ebe5f84f	7	// //
robyounger	0:fb93ebe5f84f	8	// //
robyounger	0:fb93ebe5f84f	9	// Rob Younger 26th Oct 2009, (tweaked 15th Nov 2009) //
robyounger	0:fb93ebe5f84f	10	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	11
robyounger	0:fb93ebe5f84f	12	// Generating video like it's 1982!
robyounger	0:fb93ebe5f84f	13
robyounger	0:fb93ebe5f84f	14	// Warning : this is very hacky code - just proof of concept!
robyounger	0:fb93ebe5f84f	15	// This might blow up your mbed or your TV.
robyounger	0:fb93ebe5f84f	16	// I claim no responsibility for anything :-)
robyounger	0:fb93ebe5f84f	17
robyounger	0:fb93ebe5f84f	18	// Start with a 180 Ohm resistor in series with the DAC output
robyounger	0:fb93ebe5f84f	19	// before connecting to a composite AV input,
robyounger	0:fb93ebe5f84f	20	// DAC is about 0-3.3v output, Composite in 1v p-p, with a 75 Ohm termination, so 180 Ohms is about right.
robyounger	0:fb93ebe5f84f	21
robyounger	0:fb93ebe5f84f	22	// but it also worked without any resistor for me! Start with a higher value if you aren't sure.
robyounger	0:fb93ebe5f84f	23	// More likely to burn out your mbed or TV with low/no resistor - Use at your own risk!
robyounger	0:fb93ebe5f84f	24
robyounger	0:fb93ebe5f84f	25
robyounger	0:fb93ebe5f84f	26	// HOW THIS WORKS:
robyounger	0:fb93ebe5f84f	27
robyounger	0:fb93ebe5f84f	28	// The DAC output is written as fast as possible to software generate a composite signal
robyounger	0:fb93ebe5f84f	29	// dac.write_u16() seems to take about 0.5 us: I worked this timing out using a big loop of
robyounger	0:fb93ebe5f84f	30	// dac.write_u16(0);
robyounger	0:fb93ebe5f84f	31	// ....
robyounger	0:fb93ebe5f84f	32	// dac.write_u16(0);
robyounger	0:fb93ebe5f84f	33	// dac.write_u16(0xFFFF);
robyounger	0:fb93ebe5f84f	34	// ....
robyounger	0:fb93ebe5f84f	35	// dac.write_u16(0xFFFF);
robyounger	0:fb93ebe5f84f	36	// Until I got a frequency I could measure on a multimeter.
robyounger	0:fb93ebe5f84f	37	//
robyounger	0:fb93ebe5f84f	38	// At full speed gives us about 1MHz max frequency -
robyounger	0:fb93ebe5f84f	39	// I don't have an oscilloscope to see how well this actually works, probably totally out of spec!
robyounger	0:fb93ebe5f84f	40	//
robyounger	0:fb93ebe5f84f	41	// The software just runs loads of these to generate the composite signal as fast as possible!
robyounger	0:fb93ebe5f84f	42	//
robyounger	0:fb93ebe5f84f	43	// Since a TV output is generated continuously this would use 100% CPU time.
robyounger	0:fb93ebe5f84f	44	//
robyounger	0:fb93ebe5f84f	45	// Clever to-the-metal code would do things like use the horizontal and vertical blanking
robyounger	0:fb93ebe5f84f	46	// intervals to do any required calculation. This isn't clever to-the-metal code!
robyounger	0:fb93ebe5f84f	47	// Instead, I just don't draw the bottom few percent of the TV picture, and use this free time to run code.
robyounger	0:fb93ebe5f84f	48	// This may well cause your TV to loose sync, but it works for me - I did say it was a hack!
robyounger	0:fb93ebe5f84f	49	//
robyounger	0:fb93ebe5f84f	50	// Driving the display takes 90%, main code gets 10% to play with at the end of each frame.
robyounger	0:fb93ebe5f84f	51	// Tweak these percentages up and down, but loose too many lines and the tv is much more likely to
robyounger	0:fb93ebe5f84f	52	// drop the signal, equally as you hit 100% CPU the frame calls might start to overlap and it all goes a bit wrong!
robyounger	0:fb93ebe5f84f	53	//
robyounger	0:fb93ebe5f84f	54	// This code actually starts with the end of previous frame signalling first, then all the setup, then the actual picture.
robyounger	0:fb93ebe5f84f	55	//
robyounger	0:fb93ebe5f84f	56	// It's coded up as a routine that draws a whole frame (field), which is called from main on a timer interrupt (at 50Hz for PAL)
robyounger	0:fb93ebe5f84f	57	// This makes it easy to have a main routing that can operate normally, without you having to worry (too much) about the timing involved.
robyounger	0:fb93ebe5f84f	58	// The picture elements of the signal are created by dumping a global frame buffer over to the DAC:
robyounger	0:fb93ebe5f84f	59	// unsigned short int framebuffer[HEIGHT][WIDTH];
robyounger	0:fb93ebe5f84f	60	// The values in this framebuffer are the actual composite signal, NOT just shades of gray!
robyounger	0:fb93ebe5f84f	61	// In other words, only write values between 0x56DB (black) and 0xFFFF (bright white).
robyounger	0:fb93ebe5f84f	62	// For this reason, it's important to initialize the buffer to all 0x56DB or above
robyounger	0:fb93ebe5f84f	63
robyounger	0:fb93ebe5f84f	64	// Yes - there's probably a much better way to do this - but you don't want to slow down the DAC writes at all.
robyounger	0:fb93ebe5f84f	65	// Adding checks or shifting the value from a normal range might be to slow - over to the real programmers to work out how to do this...
robyounger	0:fb93ebe5f84f	66
robyounger	0:fb93ebe5f84f	67	// The frame buffer is 105 pixels wide - this is just because 105 dac writes take up the time required for a horizontal tv line.
robyounger	0:fb93ebe5f84f	68	// height is more arbitrary, as we draw every scan line - but I double or quadruple scan to get squarish pixels!
robyounger	0:fb93ebe5f84f	69	// Use a modulo value in the picture write line to repeat the picture for small framebuffers.
robyounger	0:fb93ebe5f84f	70
robyounger	0:fb93ebe5f84f	71	// This program has a couple of demo routines. One draws a fractal, and the other just writes random values to the framebuffer
robyounger	0:fb93ebe5f84f	72
robyounger	0:fb93ebe5f84f	73	// A future enhancement could be to have two small framebuffers 105x64 and do double buffering? Needs to all be in fast memory though.
robyounger	0:fb93ebe5f84f	74	// The code could definitely do with some tuning as the sync delays are all a bit off...
robyounger	0:fb93ebe5f84f	75
robyounger	0:fb93ebe5f84f	76	//////////////////////////////////////////////////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	77
robyounger	0:fb93ebe5f84f	78
robyounger	0:fb93ebe5f84f	79	#include "mbed.h"
robyounger	0:fb93ebe5f84f	80
robyounger	0:fb93ebe5f84f	81	//Framebuffer size
robyounger	0:fb93ebe5f84f	82	#define WIDTH 105
robyounger	0:fb93ebe5f84f	83	#define HEIGHT 128
robyounger	0:fb93ebe5f84f	84
robyounger	0:fb93ebe5f84f	85	//TV signal generation controlling:
robyounger	0:fb93ebe5f84f	86	#define LINES 256 //Visible lines drawn to screen
robyounger	0:fb93ebe5f84f	87	#define SCAN 2 //Number of scanlines per pixel (vertical)
robyounger	0:fb93ebe5f84f	88	#define DRAWWIDTH 105 //Pixels per line
robyounger	0:fb93ebe5f84f	89
robyounger	0:fb93ebe5f84f	90	// LINES: theoretically up to 286 for PAL, 241 for NTSC). 285 seems to be about 100% CPU on PAL. Smaller values means I stop drawing the signal early.
robyounger	0:fb93ebe5f84f	91	// SCAN: controls double scan (e.g. 128 pixels to 256 lines)
robyounger	0:fb93ebe5f84f	92	// DRAWWIDTH: number of pixels to attempt to draw in a line (should be =< framebuffer WIDTH). Very timing critical - expect different values to break
robyounger	0:fb93ebe5f84f	93
robyounger	0:fb93ebe5f84f	94	// Composite signal values for DAC output. These should really be scaled for 1v peak-to-peak
robyounger	0:fb93ebe5f84f	95	#define IRE_m40 0x0000 //0volts
robyounger	0:fb93ebe5f84f	96	#define IRE_0 0x4920 //Baseline
robyounger	0:fb93ebe5f84f	97	#define IRE_7p5 0x56DB //Black
robyounger	0:fb93ebe5f84f	98	#define IRE_100 0xFFFF //White
robyounger	0:fb93ebe5f84f	99	// DAC is 10bit, but i'm using write_u16 to write to the DAC.
robyounger	0:fb93ebe5f84f	100	// IRE is a definition:
robyounger	0:fb93ebe5f84f	101	// the levels are -40 (0volts), 0 (baseline below black), 7.5 (Black), 100 (White).
robyounger	0:fb93ebe5f84f	102	// IRE -40 is 0v, 100 is 1v, so scale accordingly!
robyounger	0:fb93ebe5f84f	103
robyounger	0:fb93ebe5f84f	104	AnalogOut dac(p18); // Video out pin
robyounger	0:fb93ebe5f84f	105	Ticker timer; // Timer for calling the frame
robyounger	0:fb93ebe5f84f	106
robyounger	0:fb93ebe5f84f	107	DigitalOut led1(LED1);//Some status lights...
robyounger	0:fb93ebe5f84f	108	DigitalOut led2(LED2);
robyounger	0:fb93ebe5f84f	109	DigitalOut led3(LED3);
robyounger	0:fb93ebe5f84f	110	DigitalOut led4(LED4);
robyounger	0:fb93ebe5f84f	111
robyounger	0:fb93ebe5f84f	112	// Framebuffer actually has video signal levels in it - not just grayscale data
robyounger	0:fb93ebe5f84f	113	// This means it must be initialised to at least all black IRE_7p5 before it's used.
robyounger	0:fb93ebe5f84f	114	// zero values will likely kill the output and TV will loose sync.
robyounger	0:fb93ebe5f84f	115	unsigned short int framebuffer[HEIGHT][WIDTH];
robyounger	0:fb93ebe5f84f	116
robyounger	0:fb93ebe5f84f	117
robyounger	0:fb93ebe5f84f	118
robyounger	0:fb93ebe5f84f	119	/////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	120	//Software composite signal generation (very timing specific)
robyounger	0:fb93ebe5f84f	121	/////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	122
robyounger	0:fb93ebe5f84f	123	void createframe() {
robyounger	0:fb93ebe5f84f	124
robyounger	0:fb93ebe5f84f	125	// Procedure to create a output frame to a tv - needs to run on a very regular sync (e.g. 50Hz or 60Hz)
robyounger	0:fb93ebe5f84f	126	// Using the DAC to create this output, which seems to happily run at 2MHz update
robyounger	0:fb93ebe5f84f	127	// dac.write_u16 seems to take almost spot on 0.5us, so I'm using multiples of this to create a signal.
robyounger	0:fb93ebe5f84f	128
robyounger	0:fb93ebe5f84f	129	// Could maybe be done with timing precision through multiple digital outputs and a resistor ladder to create an external DAC, but this didn't need any external components!
robyounger	0:fb93ebe5f84f	130
robyounger	0:fb93ebe5f84f	131	// Someone with an oscilloscope can tweak this to get the delays more up to standard!
robyounger	0:fb93ebe5f84f	132
robyounger	0:fb93ebe5f84f	133	// TV signal specs
robyounger	0:fb93ebe5f84f	134
robyounger	0:fb93ebe5f84f	135	// For 50Hz PAL, each line takes up 64us, and there are 625 lines, but split into two fields of about 312 lines.
robyounger	0:fb93ebe5f84f	136	// I'm treating both fields exactly the same, so we have a 312(ish) lines at 50Hz.
robyounger	0:fb93ebe5f84f	137	// NTSC is actually very similar but with slightly different timings/counts. (525 lines at 60Hz).
robyounger	0:fb93ebe5f84f	138
robyounger	0:fb93ebe5f84f	139	// Some info found through google:
robyounger	0:fb93ebe5f84f	140
robyounger	0:fb93ebe5f84f	141	//525line (NTSC) - required timing in us for a line
robyounger	0:fb93ebe5f84f	142	//NAME LENGTH LEVEL
robyounger	0:fb93ebe5f84f	143	//Front porch 1.5 IRE_0
robyounger	0:fb93ebe5f84f	144	//Sync Tip 4.7 IRE_m40
robyounger	0:fb93ebe5f84f	145	//Breezeway 0.6 IRE_0
robyounger	0:fb93ebe5f84f	146	//Color Burst 2.5 IRE_0
robyounger	0:fb93ebe5f84f	147	//Back Porch 1.6 IRE_0
robyounger	0:fb93ebe5f84f	148	//Active Video 52.6 IRE_7p5 - IRE100
robyounger	0:fb93ebe5f84f	149
robyounger	0:fb93ebe5f84f	150	//Total line time = 63.5us ( * half of 525 lines * 60Hz)
robyounger	0:fb93ebe5f84f	151
robyounger	0:fb93ebe5f84f	152	//625line (PAL) - required timing in us for a line
robyounger	0:fb93ebe5f84f	153	//NAME LENGTH LEVEL
robyounger	0:fb93ebe5f84f	154	//Front porch 1.65 IRE_0
robyounger	0:fb93ebe5f84f	155	//Sync Tip 4.7 IRE_m40
robyounger	0:fb93ebe5f84f	156	//Breezeway 0.9 IRE_0
robyounger	0:fb93ebe5f84f	157	//Color Burst 2.25 IRE_0
robyounger	0:fb93ebe5f84f	158	//Back Porch 2.55 IRE_0
robyounger	0:fb93ebe5f84f	159	//Active Video 51.95 IRE_7p5 - IRE100
robyounger	0:fb93ebe5f84f	160
robyounger	0:fb93ebe5f84f	161	//Total line time = 64us ( * half of 625 lines * 50Hz)
robyounger	0:fb93ebe5f84f	162
robyounger	0:fb93ebe5f84f	163	// There actually seem to be a lot of variations on this, but they all seem roughly the same.
robyounger	0:fb93ebe5f84f	164
robyounger	0:fb93ebe5f84f	165	// Colour needs a precision ~4MHz carrier signal applied over the 'color burst' and active video
robyounger	0:fb93ebe5f84f	166	// with precise phase and amplitude control (sounds like a lot of work!)
robyounger	0:fb93ebe5f84f	167
robyounger	0:fb93ebe5f84f	168	// So for colour, Use svideo, VGA, or use 3 of these signals to generate an RGB scart signal?
robyounger	0:fb93ebe5f84f	169
robyounger	0:fb93ebe5f84f	170	//The basic frame format is
robyounger	0:fb93ebe5f84f	171	//1) few lines of special start pulses,
robyounger	0:fb93ebe5f84f	172	//2) some off screen lines, which had things like teletext/close captions
robyounger	0:fb93ebe5f84f	173	//3) the tv picture bit you see,
robyounger	0:fb93ebe5f84f	174	//4) some special pulses to say end of screen, go back to the top.
robyounger	0:fb93ebe5f84f	175	// Then straight back to 1 for the next frame.
robyounger	0:fb93ebe5f84f	176
robyounger	0:fb93ebe5f84f	177	// To get the timing right - I do this:
robyounger	0:fb93ebe5f84f	178	//4) some special pulses to say end of screen, go back to the top.
robyounger	0:fb93ebe5f84f	179	//1) few lines of special start pulses,
robyounger	0:fb93ebe5f84f	180	//2) some off screen lines, which had things like teletext/close captions
robyounger	0:fb93ebe5f84f	181	//3) the tv picture bit you see,
robyounger	0:fb93ebe5f84f	182
robyounger	0:fb93ebe5f84f	183	// You can get away dropping the last few lines of 3)
robyounger	0:fb93ebe5f84f	184	// I use this to drop back to the main program to run as normal.
robyounger	0:fb93ebe5f84f	185
robyounger	0:fb93ebe5f84f	186	// Ideally you'd use the few cycles between each line to do stuff, but that's going to be hard to get timing right.
robyounger	0:fb93ebe5f84f	187
robyounger	0:fb93ebe5f84f	188
robyounger	0:fb93ebe5f84f	189	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	190	//Start of Frame
robyounger	0:fb93ebe5f84f	191	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	192
robyounger	0:fb93ebe5f84f	193	//Each dac.write is ~0.5us, so multiply up to create the timings.
robyounger	0:fb93ebe5f84f	194
robyounger	0:fb93ebe5f84f	195	// (This is a mix of PAL and NTSC - hack as appropriate)
robyounger	0:fb93ebe5f84f	196
robyounger	0:fb93ebe5f84f	197	// There are 21 lines per field in a vertical blanking period
robyounger	0:fb93ebe5f84f	198	// the last 4 lines of a field indicate are just before flyback
robyounger	0:fb93ebe5f84f	199	// then there are 5 blank lines for flyback itself...
robyounger	0:fb93ebe5f84f	200
robyounger	0:fb93ebe5f84f	201	//END OF A FRAME + FLYBACK + START OF NEW FRAME signalling (9 lines)
robyounger	0:fb93ebe5f84f	202	for (int i = 0; i < 6; i++) { //6 equalizing pulses (time = 6 half lines)
robyounger	0:fb93ebe5f84f	203	dac.write_u16(IRE_m40); //2.4us
robyounger	0:fb93ebe5f84f	204	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	205	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	206	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	207	// dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	208	dac.write_u16(IRE_0); //29.4us
robyounger	0:fb93ebe5f84f	209	wait_us(28);
robyounger	0:fb93ebe5f84f	210	}
robyounger	0:fb93ebe5f84f	211	for (int i = 0; i < 6; i++) {// 6 serrated vertical pulses (time = 6 half lines)
robyounger	0:fb93ebe5f84f	212	dac.write_u16(IRE_0); //2.4us
robyounger	0:fb93ebe5f84f	213	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	214	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	215	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	216	// dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	217	dac.write_u16(IRE_m40); //29.4us
robyounger	0:fb93ebe5f84f	218	wait_us(28);
robyounger	0:fb93ebe5f84f	219	}
robyounger	0:fb93ebe5f84f	220	for (int i = 0; i < 6; i++) { // 6 equalizing pulses (time = 6 half lines)
robyounger	0:fb93ebe5f84f	221	dac.write_u16(IRE_m40); //2.4us
robyounger	0:fb93ebe5f84f	222	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	223	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	224	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	225	// dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	226	dac.write_u16(IRE_0); //29.4us
robyounger	0:fb93ebe5f84f	227	wait_us(28);
robyounger	0:fb93ebe5f84f	228	}
robyounger	0:fb93ebe5f84f	229
robyounger	0:fb93ebe5f84f	230
robyounger	0:fb93ebe5f84f	231	// The lines just above the top of the picture used for setup/teletext/closed captions etc.
robyounger	0:fb93ebe5f84f	232	// about 17 lines for PAL, 12 for NTSC?
robyounger	0:fb93ebe5f84f	233	for (int i = 0; i < 17; i++) {
robyounger	0:fb93ebe5f84f	234	//10.9us (NTSC) or 12.5us (PAL) for horizontal blanking interval
robyounger	0:fb93ebe5f84f	235	dac.write_u16(IRE_0); //Front porch 1.6us
robyounger	0:fb93ebe5f84f	236	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	237	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	238	dac.write_u16(IRE_m40); //Sync Tip 4.7us
robyounger	0:fb93ebe5f84f	239	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	240	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	241	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	242	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	243	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	244	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	245	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	246	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	247	// dac.write_u16(IRE_m40); //extra for PAL timing
robyounger	0:fb93ebe5f84f	248	dac.write_u16(IRE_0); //Breezeway 0.5us
robyounger	0:fb93ebe5f84f	249	dac.write_u16(IRE_0); //ColorBurst 2.5us
robyounger	0:fb93ebe5f84f	250	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	251	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	252	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	253	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	254	dac.write_u16(IRE_m40); //Back Porch 1.6us (2.55us in PAL)
robyounger	0:fb93ebe5f84f	255	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	256	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	257	dac.write_u16(IRE_m40); //extra for PAL timing
robyounger	0:fb93ebe5f84f	258	dac.write_u16(IRE_m40); //extra for PAL timing
robyounger	0:fb93ebe5f84f	259
robyounger	0:fb93ebe5f84f	260	// for (int j = 0; j < DRAWWIDTH; j++) {
robyounger	0:fb93ebe5f84f	261	// dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	262	// } //next pixel
robyounger	0:fb93ebe5f84f	263
robyounger	0:fb93ebe5f84f	264
robyounger	0:fb93ebe5f84f	265	//Then that video signal for 52.6us (52 for PAL)
robyounger	0:fb93ebe5f84f	266	dac.write_u16(IRE_0); //Video signal for 52.6us
robyounger	0:fb93ebe5f84f	267	wait_us(51); // replaces another 104 dac.write_u16(IRE_0)
robyounger	0:fb93ebe5f84f	268	}
robyounger	0:fb93ebe5f84f	269
robyounger	0:fb93ebe5f84f	270
robyounger	0:fb93ebe5f84f	271	//Draw the actual visible lines on screen: exactly same header as previous, but followed by real video data.
robyounger	0:fb93ebe5f84f	272	// intentionally dropping the last few lines to throw some time to main()
robyounger	0:fb93ebe5f84f	273	// otherwise this loop would use 100% of CPU.
robyounger	0:fb93ebe5f84f	274	for (int i = 0; i < LINES; i++) {
robyounger	0:fb93ebe5f84f	275	//10.9us (NTSC) or 12.5us (PAL) for horizontal blanking interval
robyounger	0:fb93ebe5f84f	276	dac.write_u16(IRE_0); //Front porch 1.6us
robyounger	0:fb93ebe5f84f	277	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	278	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	279	dac.write_u16(IRE_m40); //Sync Tip 4.7us
robyounger	0:fb93ebe5f84f	280	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	281	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	282	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	283	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	284	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	285	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	286	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	287	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	288	// dac.write_u16(IRE_m40); //extra for PAL timing
robyounger	0:fb93ebe5f84f	289	dac.write_u16(IRE_0); //Breezeway 0.5us
robyounger	0:fb93ebe5f84f	290	dac.write_u16(IRE_0); //ColorBurst 2.5us
robyounger	0:fb93ebe5f84f	291	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	292	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	293	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	294	dac.write_u16(IRE_0);
robyounger	0:fb93ebe5f84f	295	dac.write_u16(IRE_m40); //Back Porch 1.6us (2.55us in PAL)
robyounger	0:fb93ebe5f84f	296	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	297	dac.write_u16(IRE_m40);
robyounger	0:fb93ebe5f84f	298	dac.write_u16(IRE_m40); //extra for PAL timing
robyounger	0:fb93ebe5f84f	299	dac.write_u16(IRE_m40); //extra for PAL timing
robyounger	0:fb93ebe5f84f	300
robyounger	0:fb93ebe5f84f	301	//Then that video signal for 52.6us (52 for PAL):
robyounger	0:fb93ebe5f84f	302
robyounger	0:fb93ebe5f84f	303	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	304	//Write out the video data
robyounger	0:fb93ebe5f84f	305	//(very timing sensitive as must last ~53us, no more or less)
robyounger	0:fb93ebe5f84f	306	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	307
robyounger	0:fb93ebe5f84f	308	// Examples:
robyounger	0:fb93ebe5f84f	309
robyounger	0:fb93ebe5f84f	310	//1) draw random shade per line
robyounger	0:fb93ebe5f84f	311	// dac.write_u16(rand() % 40000 + IRE_7p5); //Video signal for 52.6us
robyounger	0:fb93ebe5f84f	312	// wait_us(52);
robyounger	0:fb93ebe5f84f	313
robyounger	0:fb93ebe5f84f	314	//2) draw black
robyounger	0:fb93ebe5f84f	315	// dac.write_u16(IRE_7p5);
robyounger	0:fb93ebe5f84f	316	// wait_us(51);
robyounger	0:fb93ebe5f84f	317
robyounger	0:fb93ebe5f84f	318	//3) draw white
robyounger	0:fb93ebe5f84f	319	// dac.write_u16(IRE_100);
robyounger	0:fb93ebe5f84f	320	// wait_us(51);
robyounger	0:fb93ebe5f84f	321
robyounger	0:fb93ebe5f84f	322	//4) draw framebuffer
robyounger	0:fb93ebe5f84f	323
robyounger	0:fb93ebe5f84f	324	// Code here is very timing critical.
robyounger	0:fb93ebe5f84f	325
robyounger	0:fb93ebe5f84f	326	// loop count is instruction dependent, if you add some code here, it will need be a different width
robyounger	0:fb93ebe5f84f	327	// We have ~52.5us and a a dac write takes 0.5us so 104/105px seems correct.
robyounger	0:fb93ebe5f84f	328	// Trial+error shows ~100-110 pixels to be OKish on a particular old TV.
robyounger	0:fb93ebe5f84f	329
robyounger	0:fb93ebe5f84f	330	int k =(i/ SCAN ); //double scan the framebuffer, particularly convenient for 128 vertical px but 256 line resolution..
robyounger	0:fb93ebe5f84f	331
robyounger	0:fb93ebe5f84f	332	// The modulo is only needed if screen output size is bigger than framebuffer (wrapping occurs).
robyounger	0:fb93ebe5f84f	333	// Stick to powers of 2 for modulo wrapping (or likely too slow).
robyounger	0:fb93ebe5f84f	334	for (int j = 0; j < DRAWWIDTH; j++) {
robyounger	0:fb93ebe5f84f	335	dac.write_u16( framebuffer[k%128][j%128] ); //modulo used to wrap framebuffer. Keep to power of 2 =< framebuffer sizes.
robyounger	0:fb93ebe5f84f	336	} //next pixel
robyounger	0:fb93ebe5f84f	337
robyounger	0:fb93ebe5f84f	338	} //next line loop
robyounger	0:fb93ebe5f84f	339
robyounger	0:fb93ebe5f84f	340	//Default back to black when we don't bother drawing the last few lines of a frame!
robyounger	0:fb93ebe5f84f	341	dac.write_u16(IRE_7p5);
robyounger	0:fb93ebe5f84f	342	} //End of createframe routine
robyounger	0:fb93ebe5f84f	343
robyounger	0:fb93ebe5f84f	344
robyounger	0:fb93ebe5f84f	345
robyounger	0:fb93ebe5f84f	346	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	347	// randomfill the framebuffer //
robyounger	0:fb93ebe5f84f	348	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	349	void randomfill () {
robyounger	0:fb93ebe5f84f	350	for (int j = 0; j < HEIGHT; j++) {
robyounger	0:fb93ebe5f84f	351	for (int i = 0; i < WIDTH; i++) {
robyounger	0:fb93ebe5f84f	352	framebuffer[j][i] = rand();
robyounger	0:fb93ebe5f84f	353	if (framebuffer[j][i] < IRE_7p5 ) {
robyounger	0:fb93ebe5f84f	354	framebuffer[j][i] = IRE_7p5;
robyounger	0:fb93ebe5f84f	355	}
robyounger	0:fb93ebe5f84f	356	}
robyounger	0:fb93ebe5f84f	357	}
robyounger	0:fb93ebe5f84f	358	}
robyounger	0:fb93ebe5f84f	359
robyounger	0:fb93ebe5f84f	360	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	361	// blank the framebuffer //
robyounger	0:fb93ebe5f84f	362	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	363	void blankfill () {
robyounger	0:fb93ebe5f84f	364	for (int j = 0; j < HEIGHT; j++) {
robyounger	0:fb93ebe5f84f	365	for (int i = 0; i < WIDTH; i++) {
robyounger	0:fb93ebe5f84f	366	framebuffer[j][i] = IRE_7p5;
robyounger	0:fb93ebe5f84f	367	//framebuffer[j][i] = IRE_100;
robyounger	0:fb93ebe5f84f	368	}
robyounger	0:fb93ebe5f84f	369	}
robyounger	0:fb93ebe5f84f	370	}
robyounger	0:fb93ebe5f84f	371
robyounger	0:fb93ebe5f84f	372	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	373	// zooming mandelbot fractal in the framebuffer //
robyounger	0:fb93ebe5f84f	374	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	375
robyounger	0:fb93ebe5f84f	376	void mandelbrot () {
robyounger	0:fb93ebe5f84f	377	//Mandelbrot escape time algorithm (doubles+iteration=slow)
robyounger	0:fb93ebe5f84f	378	//Taken from wikipedia pseudocode,
robyounger	0:fb93ebe5f84f	379	//tweaked by using the speeded up version that google found on geocities
robyounger	0:fb93ebe5f84f	380	//(oops - Geocities has shut down in the 3 weeks since I wrote this! first time I've used it in years!)
robyounger	0:fb93ebe5f84f	381	//http://www.geocities.com/CapeCanaveral/5003/Mandel.txt
robyounger	0:fb93ebe5f84f	382	//then put in a loop to zoom in on a intersting co-ords point i saw elsewhere...
robyounger	0:fb93ebe5f84f	383	double zoom;
robyounger	0:fb93ebe5f84f	384	for (int z = 0; z < 200; z++) {//2^50 is quite a lot of zoom - thats why you need precision!
robyounger	0:fb93ebe5f84f	385	zoom= pow((double)1.2,z);
robyounger	0:fb93ebe5f84f	386
robyounger	0:fb93ebe5f84f	387	led1=0;
robyounger	0:fb93ebe5f84f	388	led2=0;
robyounger	0:fb93ebe5f84f	389	led3=0;
robyounger	0:fb93ebe5f84f	390	led4=0;
robyounger	0:fb93ebe5f84f	391
robyounger	0:fb93ebe5f84f	392	double x,y;
robyounger	0:fb93ebe5f84f	393	double x0,y0;
robyounger	0:fb93ebe5f84f	394	// double xtemp;
robyounger	0:fb93ebe5f84f	395	double xsq;
robyounger	0:fb93ebe5f84f	396	double ysq;
robyounger	0:fb93ebe5f84f	397
robyounger	0:fb93ebe5f84f	398	unsigned short int iteration = 0;
robyounger	0:fb93ebe5f84f	399	unsigned short int max_iteration = (z*2)+20; //arbitrary scaling so there are more interation allowed as you zoom
robyounger	0:fb93ebe5f84f	400	for (int j = 0; j < HEIGHT; j++) {
robyounger	0:fb93ebe5f84f	401	//little status hack as as drawing fractals (particularly with doubles on only 10% of a cpu is slow!)
robyounger	0:fb93ebe5f84f	402	if (j== (( HEIGHT /4)-1)) {
robyounger	0:fb93ebe5f84f	403	led1=1;
robyounger	0:fb93ebe5f84f	404	} else if (j==(( HEIGHT /2)-1)) {
robyounger	0:fb93ebe5f84f	405	led2=1;
robyounger	0:fb93ebe5f84f	406	} else if (j==(3*( HEIGHT /4)-1)) {
robyounger	0:fb93ebe5f84f	407	led3=1;
robyounger	0:fb93ebe5f84f	408	} else if (j==( HEIGHT -1)) {
robyounger	0:fb93ebe5f84f	409	led4=1;
robyounger	0:fb93ebe5f84f	410	}
robyounger	0:fb93ebe5f84f	411	//end of little status hack
robyounger	0:fb93ebe5f84f	412
robyounger	0:fb93ebe5f84f	413
robyounger	0:fb93ebe5f84f	414	for (int i = 0; i < WIDTH; i++) {
robyounger	0:fb93ebe5f84f	415	// x0=(((float) i) -32.0)/32.0;//redefine 0to63 as -1to+1 mandelbrot window
robyounger	0:fb93ebe5f84f	416	// y0=(((float) j) -32.0)/32.0;//redefine 0to63 as -1to+1 mandelbrot window
robyounger	0:fb93ebe5f84f	417	//-1.865725138512217656771 moves center point to something interesting
robyounger	0:fb93ebe5f84f	418	x0=((((double) i) - ( WIDTH /2)) /zoom)-1.865725138512217656771;//redefine 0to63 as -1to+1 mandelbrot window
robyounger	0:fb93ebe5f84f	419	y0=(((double) j) - ( HEIGHT /2)) /zoom;//redefine 0to63 as -1to+1 mandelbrot window
robyounger	0:fb93ebe5f84f	420	iteration = 0;
robyounger	0:fb93ebe5f84f	421
robyounger	0:fb93ebe5f84f	422	//Standard version of mandelbrot loop based on wikipedia pseudocode
robyounger	0:fb93ebe5f84f	423	// x=0;
robyounger	0:fb93ebe5f84f	424	// y=0;
robyounger	0:fb93ebe5f84f	425	// while ( ((xx + yy) <= (2*2)) && (iteration < max_iteration) ) {
robyounger	0:fb93ebe5f84f	426	// xtemp = xx - yy + x0;
robyounger	0:fb93ebe5f84f	427	// y = 2xy + y0;
robyounger	0:fb93ebe5f84f	428	// x = xtemp;
robyounger	0:fb93ebe5f84f	429	// iteration++;
robyounger	0:fb93ebe5f84f	430	// }
robyounger	0:fb93ebe5f84f	431
robyounger	0:fb93ebe5f84f	432	//Speedy version of main mandelbrot loop (algorithm from geocities page)
robyounger	0:fb93ebe5f84f	433	x=x0+x0x0-y0y0;
robyounger	0:fb93ebe5f84f	434	y=y0+x0y0+x0y0;
robyounger	0:fb93ebe5f84f	435	for (iteration=0;iteration<max_iteration && (ysq=yy)+(xsq=xx)<4;iteration++,y=y0+xy+xy,x=x0-ysq+xsq) ;
robyounger	0:fb93ebe5f84f	436
robyounger	0:fb93ebe5f84f	437	//Iteration count determines color (clamp max iteration to zero, and normalize for black to white)
robyounger	0:fb93ebe5f84f	438	framebuffer[j][i] = (( iteration == max_iteration ) ? (IRE_7p5) : (IRE_7p5 + ((iteration%20)*2000)) );
robyounger	0:fb93ebe5f84f	439	}
robyounger	0:fb93ebe5f84f	440	}
robyounger	0:fb93ebe5f84f	441	}//zoom loop
robyounger	0:fb93ebe5f84f	442	}
robyounger	0:fb93ebe5f84f	443
robyounger	0:fb93ebe5f84f	444
robyounger	0:fb93ebe5f84f	445	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	446	// main() showing use framebuffer //
robyounger	0:fb93ebe5f84f	447	// Puts a grayscale pic in it //
robyounger	0:fb93ebe5f84f	448	////////////////////////////////////////////////////////////
robyounger	0:fb93ebe5f84f	449
robyounger	0:fb93ebe5f84f	450	int main() {
robyounger	0:fb93ebe5f84f	451
robyounger	0:fb93ebe5f84f	452	blankfill(); //set framebuffer to blank values
robyounger	0:fb93ebe5f84f	453
robyounger	0:fb93ebe5f84f	454	timer.attach_us(&createframe,20000);//attach the display (at 50Hz)
robyounger	0:fb93ebe5f84f	455
robyounger	0:fb93ebe5f84f	456	// int attached=0; //attach frame
robyounger	0:fb93ebe5f84f	457	// //If you had a lot of setup in a main game loop, you could do something like this:
robyounger	0:fb93ebe5f84f	458	// if (attached==0) {
robyounger	0:fb93ebe5f84f	459	// timer.attach_us(&createframe,20000);
robyounger	0:fb93ebe5f84f	460	// attached=1;
robyounger	0:fb93ebe5f84f	461	// }
robyounger	0:fb93ebe5f84f	462
robyounger	0:fb93ebe5f84f	463	//Program loop
robyounger	0:fb93ebe5f84f	464	while (1) {
robyounger	0:fb93ebe5f84f	465	// Add you own demo code here. Expect it to get regularly interupted by the screen draw call!
robyounger	0:fb93ebe5f84f	466	// very simple code can run at full fps.
robyounger	0:fb93ebe5f84f	467	//Example - change HEIGHT to 64 and SCAN to 4 and use randomfill instead of mandelbrot...
robyounger	0:fb93ebe5f84f	468
robyounger	0:fb93ebe5f84f	469	//randomfill(); //random pixel fill
robyounger	0:fb93ebe5f84f	470	mandelbrot(); //mandelbrot procedure is a 200 loop zoom so takes ages - and each scene redraw takes a few seconds!
robyounger	0:fb93ebe5f84f	471	} //while
robyounger	0:fb93ebe5f84f	472
robyounger	0:fb93ebe5f84f	473	} //main
robyounger	0:fb93ebe5f84f	474
robyounger	0:fb93ebe5f84f	475

Repository toolbox

Export to desktop IDE

Build repository

Repository details

Type:	Program
Mbed OS support:	Mbed 2 deprecated
Created:	15 Nov 2009
Imports:	5
Forks:	0
Commits:	1
Dependents:	0
Dependencies:	1
Followers:	1

composite.cpp@0:fb93ebe5f84f, 2009-11-15 (annotated)

Who changed what in which revision?

Repository toolbox

Repository details

Important Information for this Arm website

Access Warning