bitbuffer decoding

[habub]

Hello,
Sorry if these are basic. Just warming up...

1. Bitbuffer

• How are the sync and gap words ("y=", "g=") reresented in the bitbuffer?
• What is the row delimiter in a bitbuffer?
• When/how does a bitbuffer end? What is the bitbuffer end delimiter?

2. Decoders

• How does the program decide which of the registered decoders (-R) to use for a signal?
• Can mutiple decoders be used on the same input signal? considering the signal can match more than 1 decoder?

Thanks!

[zuckschwerdt]

A sync or gap will break into a new row and sync also sets a sync counter (syncs_before_row[i]) on the row.
Rows have a given length (bits_per_row[i]). The Bitbuffers have a given number of rows (num_rows). S.a.

rtl_433/include/bitbuffer.h

Lines 32 to 39 in 5f76eae

	/// Bit buffer.
	typedef struct bitbuffer {
	uint16_t num_rows; ///< Number of active rows
	uint16_t free_row; ///< Index of next free row
	uint16_t bits_per_row[BITBUF_ROWS]; ///< Number of active bits per row
	uint16_t syncs_before_row[BITBUF_ROWS]; ///< Number of sync pulses before row
	bitarray_t bb; ///< The actual bits buffer
	} bitbuffer_t;

All decoders with matching "timings" are run. This means deciding if FSK / OOK is present and then trying if the timings can extract bits.

[habub]

Thanks!
I'm not sure I understand how to identify sync vs gap, and the reset signals.
When trying to decode this signal assuming ook_pwm, I get:
{178} FE / 9F 6D B3 29 FF / 9F EF DF BF FF / 9C BF ED EA E9 BA B7 7B C (without setting gap)
Should this transmission be 1 bitbuffer or more? Does each "/" represent a new row?

[zuckschwerdt]

That's not PWM, there is data in the gaps. It's PCM (125 µs) with MC, and there is a (de-)synch of 6 bit 111000 (which is not valid MC and thus a de-synch). Looking at that it's three or four transmissions or rows.

Use PCM with 125 short/long. Then put it in a BitBench and break in the preamble, use a match (e.g. 55c) to align.
But you see the code is broken, invalid MC (there must not be an 00 or 11 parts), bad reception.

[habub]

Okay, wow....
I'll give it a try

[habub]

Hi,
Rgarding your reply:

A sync or gap will break into a new row and sync also sets a sync counter (syncs_before_row[i]) on the row. Rows have a given length (bits_per_row[i]). The Bitbuffers have a given number of rows (num_rows). S.a.

Does this mean every decoder has a different bitbuffer structure? Since gaps and rows are unique for each decoder (y=, g=, r=). I thought bitbuffer is a more raw bitstream, prior to the deocding stage. Is this correct?

[zuckschwerdt]

The bitbuffer is a raw bitstream with some meta-data, e.g. where syncs and long gaps occured.

[habub]

One last question on this thread...

I decode the row values ( bitbuffer->bb[row] ) as a decimal number. How can I get (or convert) the Hex values of a row?
So it will appear like in the analyzers:
bitbuffer:: Number of rows: 2
[00] { 8} ff : 11111111
[01] {26} 9e 37 ed c0 : 10011110 00110111 11101101 11

[zuckschwerdt]

Byte values are not decimal numbers, that's just one option to printf them ("%d") and hex would be "%x".
To print debug values in a decoder you likely want

decoder_log_bitbuffer(decoder, 0, __func__, bitbuffer, "Rows Debug");

[habub]

I want to compare my data (in hex) to the bitbuffer data. Not print.
For example:

my_data = 0x 9E 37 ED C0
if ( my_data == bitbuffer->bb[i] ) ...

Which type should I declare my_data?

[merbanan]

This is a C-language question and this is not really the place for that. But if you want to compare you can use the uint8_t type.

uint8_t my_data = { 0x9E, 0x37 ....}

Then compare against bitbuffer->bb[0][0] which also should be uint8_t. But we have other tools for handling this. I suggest you read through a couple of decoders to see what is available.

[habub]

Thanks. You're correct, I'll brush up on my programming skills. It's been a long time...

[sp372]

interesting