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Mode C1 datagram type B is supported now
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@xaelsouth
xaelsouth committed Dec 13, 2019
1 parent 2453cd8 commit 6a04c45
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Showing 2 changed files with 133 additions and 12 deletions.
11 changes: 8 additions & 3 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -40,14 +40,14 @@ Before building Android version the SDK and NDK have to be installed. See androi

Usage
-----
To save IQ-stream on disk and decode them off-line:
To save an IQ-stream on disk and decode that off-line:

* rtl_sdr samples.bin -f 868.9M -s 1600000
* rtl_sdr samples.bin -f 868.95M -s 1600000
* cat samples.bin | build/rtl_wmbus

To run continuously:

* rtl_sdr -f 868.9M -s 1600000 - 2>/dev/null | build/rtl_wmbus
* rtl_sdr -f 868.95M -s 1600000 - 2>/dev/null | build/rtl_wmbus

To count "good" (no 3 out of 6 errors, no checksum errors) packets:

Expand All @@ -59,6 +59,11 @@ samples2.bin is a "live" example with two devices received.

On Android first the driver must be started with options given above. IQ-data goes to a port which is would be already set by driver settings. Use get_net to get IQ-data into rtl_wmbus.

Bugfixing
-----
Mode C1 datagram type B is supported now - thanks to Fredrik Öhrström for spotting this bug and for providing raw datagram samples.
An another thanks to Kjell Braden (afflux) and to carlos62 for the idea how to fix this.

License
-------

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134 changes: 125 additions & 9 deletions t1_c1_packet_decoder.h
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@
#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <time.h>

Expand Down Expand Up @@ -237,6 +238,7 @@ static struct
unsigned err_3outof: 1;
unsigned crc_ok: 1;
unsigned c1_packet: 1;
unsigned b_frame_type: 1;
};
};
unsigned l;
Expand All @@ -247,12 +249,28 @@ static struct
char timestamp[64];
} t1_c1_packet_decoder_work = {.state = &states[0]}; // idle

int get_mode_a_tlg_length(uint8_t lfield)
{
return 1 + (int)lfield + (((int)lfield - 10 + 15)/16 + 1) * 2;
}

int get_mode_b_tlg_length(uint8_t lfield)
{
/* L-field of frame type B is given including data and CRC bytes but the length byte itself. */
return 1 + (int)lfield;
}

static void reset_t1_c1_packet_decoder(void)
{
memset(&t1_c1_packet_decoder_work, 0, sizeof(t1_c1_packet_decoder_work));
t1_c1_packet_decoder_work.state = &states[0];
}

static void idle(unsigned bit)
{
if (!(bit & PACKET_PREAMBLE_DETECTED_MASK))
{
t1_c1_packet_decoder_work.state = &states[0]; // idle
reset_t1_c1_packet_decoder();
}
}

Expand Down Expand Up @@ -299,17 +317,26 @@ static void rx_low_nibble_last_lfield_bit(unsigned bit)

if (t1_c1_packet_decoder_work.L == 0xFFu || byte == 0xFFu)
{
if (t1_c1_packet_decoder_work.mode == C1_MODE_A || t1_c1_packet_decoder_work.mode == C1_MODE_B)
if (t1_c1_packet_decoder_work.mode == C1_MODE_A)
{
t1_c1_packet_decoder_work.b_frame_type = 0;
t1_c1_packet_decoder_work.state = &states[26]; // c1_rx_first_mode_bit
}
else if (t1_c1_packet_decoder_work.mode == C1_MODE_B)
{
t1_c1_packet_decoder_work.b_frame_type = 1;
t1_c1_packet_decoder_work.state = &states[26]; // c1_rx_first_mode_bit
}
else
{
t1_c1_packet_decoder_work.state = &states[0]; // idle
reset_t1_c1_packet_decoder();
}
}
else
{
t1_c1_packet_decoder_work.b_frame_type = 0;
t1_c1_packet_decoder_work.c1_packet = 0;

t1_c1_packet_decoder_work.L |= byte;
t1_c1_packet_decoder_work.l = 0;
t1_c1_packet_decoder_work.packet[t1_c1_packet_decoder_work.l++] = t1_c1_packet_decoder_work.L;
Expand Down Expand Up @@ -389,7 +416,7 @@ static void c1_rx_last_mode_bit(unsigned bit)
}
else
{
t1_c1_packet_decoder_work.state = &states[0]; // idle
reset_t1_c1_packet_decoder();
}
}

Expand All @@ -406,7 +433,14 @@ static void c1_rx_last_lfield_bit(unsigned bit)
t1_c1_packet_decoder_work.L = t1_c1_packet_decoder_work.byte;
t1_c1_packet_decoder_work.l = 0;
t1_c1_packet_decoder_work.packet[t1_c1_packet_decoder_work.l++] = t1_c1_packet_decoder_work.L;
t1_c1_packet_decoder_work.L = FULL_TLG_LENGTH_FROM_L_FIELD[t1_c1_packet_decoder_work.L];
if (t1_c1_packet_decoder_work.b_frame_type)
{
t1_c1_packet_decoder_work.L = get_mode_b_tlg_length(t1_c1_packet_decoder_work.L);
}
else
{
t1_c1_packet_decoder_work.L = FULL_TLG_LENGTH_FROM_L_FIELD[t1_c1_packet_decoder_work.L];
}
}

static void c1_rx_first_data_bit(unsigned bit)
Expand Down Expand Up @@ -481,6 +515,36 @@ static bool check_calc_crc_wmbus(const uint8_t *data, size_t datalen)
return crc_ok;
}

static bool check_calc_crc_wmbus_b_frame_type(const uint8_t *data, size_t datalen)
{
bool crc_ok = (datalen >= 12);
uint16_t crc1, crc2;

/* The CRC field of Block 2 is calculated on the _concatenation_
of Block 1 and Block 2 data. */
while (crc_ok && datalen)
{
if (datalen >= 128)
{
crc1 = calc_crc_wmbus(data, 126);
crc2 = (data[126] << 8) | (data[127]);
data += 128;
datalen -= 128;
crc_ok = (crc1 == crc2);
}
else
{
crc1 = calc_crc_wmbus(data, datalen-2);
crc2 = (data[datalen-2] << 8) | (data[datalen-1]);
data += datalen;
datalen -= datalen;
crc_ok = (crc1 == crc2);
}
}

return crc_ok;
}

/** @brief Strip CRCs in place. */
static unsigned cook_pkt(uint8_t *data, unsigned datalen)
{
Expand Down Expand Up @@ -523,6 +587,44 @@ static unsigned cook_pkt(uint8_t *data, unsigned datalen)
return dstlen;
}

/** @brief Strip CRCs in place. */
static unsigned cook_pkt_b_frame_type(uint8_t *data, unsigned datalen)
{
uint8_t *dst = data;
unsigned dstlen = 0;

if (datalen >= 12)
{
while (datalen)
{
/* The CRC field of Block 2 is calculated on the _concatenation_
of Block 1 and Block 2 data. */
if (datalen >= 128)
{
memmove(dst, data, 126);

dst += 126;
dstlen += 126;

data += 128;
datalen -= 128;
}
else
{
memmove(dst, data, datalen-2);

dst += (datalen-2);
dstlen += (datalen-2);

data += datalen;
datalen -= datalen;
}
}
}

return dstlen;
}

static inline uint32_t get_serial(const uint8_t *const packet)
{
uint32_t serial;
Expand All @@ -544,7 +646,14 @@ static void t1_c1_packet_decoder(unsigned bit, unsigned rssi)
}
else if (*t1_c1_packet_decoder_work.state == done)
{
t1_c1_packet_decoder_work.crc_ok = check_calc_crc_wmbus(t1_c1_packet_decoder_work.packet, t1_c1_packet_decoder_work.L) ? 1 : 0;
if (t1_c1_packet_decoder_work.b_frame_type)
{
t1_c1_packet_decoder_work.crc_ok = check_calc_crc_wmbus_b_frame_type(t1_c1_packet_decoder_work.packet, t1_c1_packet_decoder_work.L) ? 1 : 0;
}
else
{
t1_c1_packet_decoder_work.crc_ok = check_calc_crc_wmbus(t1_c1_packet_decoder_work.packet, t1_c1_packet_decoder_work.L) ? 1 : 0;
}

fprintf(stdout, "%s;%u;%u;%s;%u;%u;%08X;", t1_c1_packet_decoder_work.c1_packet ? "C1": "T1",
t1_c1_packet_decoder_work.crc_ok,
Expand All @@ -561,23 +670,30 @@ static void t1_c1_packet_decoder(unsigned bit, unsigned rssi)
#endif

#if 1
t1_c1_packet_decoder_work.L = cook_pkt(t1_c1_packet_decoder_work.packet, t1_c1_packet_decoder_work.L);
if (t1_c1_packet_decoder_work.b_frame_type)
{
t1_c1_packet_decoder_work.L = cook_pkt_b_frame_type(t1_c1_packet_decoder_work.packet, t1_c1_packet_decoder_work.L);
}
else
{
t1_c1_packet_decoder_work.L = cook_pkt(t1_c1_packet_decoder_work.packet, t1_c1_packet_decoder_work.L);
}
fprintf(stdout, "0x");
for (size_t l = 0; l < t1_c1_packet_decoder_work.L; l++) fprintf(stdout, "%02x", t1_c1_packet_decoder_work.packet[l]);
#endif

fprintf(stdout, "\n");
fflush(stdout);

t1_c1_packet_decoder_work.state = &states[0]; // idle
reset_t1_c1_packet_decoder();
}
else
{
// Stop receiving packet if current rssi below threshold.
// The current packet seems to be collided with an another one.
if (rssi < PACKET_CAPTURE_THRESHOLD)
{
t1_c1_packet_decoder_work.state = &states[0]; // idle
reset_t1_c1_packet_decoder();
}
}
}
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