MODE_HOLD is not the place for anything like this.
If you wanted to try to make something like this work, you would do it in case MODE_DATA, where the incoming data bytes are transferred to the WS2801:
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if(bytesBuffered > 0) {
SPDR = buffer[indexOut++]; // Issue next byte
bytesBuffered--;
bytesRemaining--;
spiFlag = 1;
}
You would need to declare another array to contain the previous data packet. There's a long comment block at line 42 that gives a description of the data packets that come from the host:
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// … The host software will need to
// generate a compatible header: immediately following the magic word
// are three bytes: a 16-bit count of the number of LEDs (high byte
// first) followed by a simple checksum value (high byte XOR low byte
// XOR 0x55). LED data follows, 3 bytes per LED, in order R, G, B,
// where 0 = off and 255 = max brightness.
The header is checked in case MODE_HEADER. The LED data is processed in case MODE_DATA.
So, you would declare an array large enough to hold a complete packet's worth of LED data.
You need a boolean value - call it "noChange" - initialized to true.
You also need a counter. If "noChange" is still true after you make it through an entire packet, then you increment the counter. If "noChange" is false, then you reset the counter to 0.
Before copying a byte out to SPDR, you would first compare it against the corresponding byte in your "previous" data packet. If the two bytes are equal, you do not change the value of "noChange". If the two bytes are different, you set "noChange" to false. An easy way to do this is:
noChange = noChange & (<old byte> == <new byte>);
If noChange is false, you copy the new byte into the "previous" data packet buffer. (or don't waste time checking noChange - just copy it anyway).
Down in the ELSE clause (comment "// End of data -- issue latch:") is where you check the value of noChange and increment or reset your counter.
Pick a value where you want to turn the lights off. When the counter gets up to that value, you decide that the picture is paused, and set a "lightsOut" flag.
To avoid overflow problems, you probably should stop incrementing the counter once it gets to this point.
Now, you want to turn the lights off. Probably the simplest way to do this is to put a test into the same loop where you compare the data bytes. If your "lightsOut" flag is set, then instead of copying a data byte to SPDR, write a zero to it instead. You still want to keep doing all the "noChange" comparisons, so that you know when the picture starts changing again. When "noChange" starts ending up false, you will reset your counter and clear your "lightsOut" flag, and the lights will start operating normally again.
You're going to have to be careful to always increment indexOut properly, and in the right places too.
Good luck!
