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Detect full 48 bits of last data frame in a transmission

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While testing new support for DV Fast Data, I ran across a particular
image that reliably generated a bit sequence that the MDMVM firmware
interpreted as an end-of-transmission.  I dug a bit and discovered
that MMDVM only matches on 32 bits of the last data frame instead of
the full 48 bits.

See http://www.arrl.org/files/file/D-STAR.pdf section 2.1.2, item (6)
for details.
This commit is contained in:
Tim Stewart 2020-12-05 19:08:30 -05:00
parent fb4c543211
commit 0f7a64115d
2 changed files with 18 additions and 3 deletions
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20
DStarRX.cpp
View file

@ -40,8 +40,8 @@ const uint32_t DATA_SYNC_MASK = 0x00FFFFFFU;
const uint8_t DATA_SYNC_ERRS = 3U;
// D-Star bit order version of 0x55 0x55 0xC8 0x7A
const uint32_t END_SYNC_DATA = 0xAAAA135EU;
const uint32_t END_SYNC_MASK = 0xFFFFFFFFU;
const uint64_t END_SYNC_DATA = 0x0000AAAAAAAA135EU;
const uint64_t END_SYNC_MASK = 0x0000FFFFFFFFFFFFU;
const uint8_t END_SYNC_ERRS = 1U;
const uint8_t BIT_MASK_TABLE0[] = {0x7FU, 0xBFU, 0xDFU, 0xEFU, 0xF7U, 0xFBU, 0xFDU, 0xFEU};
@ -239,6 +239,7 @@ const uint16_t CCITT_TABLE[] = {
CDStarRX::CDStarRX() :
m_rxState(DSRXS_NONE),
m_patternBuffer(0x00U),
m_patternBuffer64(0x00U),
m_rxBuffer(),
m_rxBufferBits(0U),
m_dataBits(0U),
@ -256,6 +257,7 @@ void CDStarRX::reset()
{
m_rxState = DSRXS_NONE;
m_patternBuffer = 0x00U;
m_patternBuffer64 = 0x00U;
m_rxBufferBits = 0U;
m_dataBits = 0U;
}
@ -283,6 +285,10 @@ void CDStarRX::processNone(bool bit)
if (bit)
m_patternBuffer |= 0x01U;
m_patternBuffer64 <<= 1;
if (bit)
m_patternBuffer64 |= 0x01U;
// Fuzzy matching of the preamble sync sequence
if (countBits32((m_patternBuffer & PREAMBLE_MASK) ^ PREAMBLE_DATA) <= PREAMBLE_ERRS) {
@ -329,6 +335,10 @@ void CDStarRX::processHeader(bool bit)
if (bit)
m_patternBuffer |= 0x01U;
m_patternBuffer64 <<= 1;
if (bit)
m_patternBuffer64 |= 0x01U;
WRITE_BIT2(m_rxBuffer, m_rxBufferBits, bit);
m_rxBufferBits++;
@ -363,6 +373,10 @@ void CDStarRX::processData(bool bit)
if (bit)
m_patternBuffer |= 0x01U;
m_patternBuffer64 <<= 1;
if (bit)
m_patternBuffer64 |= 0x01U;
WRITE_BIT2(m_rxBuffer, m_rxBufferBits, bit);
m_rxBufferBits++;
@ -370,7 +384,7 @@ void CDStarRX::processData(bool bit)
reset();
// Fuzzy matching of the end frame sequences
if (countBits32((m_patternBuffer & END_SYNC_MASK) ^ END_SYNC_DATA) <= END_SYNC_ERRS) {
if (countBits64((m_patternBuffer64 & END_SYNC_MASK) ^ END_SYNC_DATA) <= END_SYNC_ERRS) {
DEBUG1("DStarRX: Found end sync in Data");
io.setDecode(false);

1
DStarRX.h
View file

@ -41,6 +41,7 @@ public:
private:
DSRX_STATE m_rxState;
uint32_t m_patternBuffer;
uint64_t m_patternBuffer64;
uint8_t m_rxBuffer[DSTAR_BUFFER_LENGTH_BITS / 8U];
unsigned int m_rxBufferBits;
unsigned int m_dataBits;