michele/DigiRadio
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Fix FM RDS: station name/RadioText never decoded, three stacked bugs

Browse Source 
GET /api/tuner/status and the full FM band scan always returned an
empty station_name, on every frequency, regardless of signal quality
-- confirmed live on multiple >35 dB SNR channels before this fix.
Three independent problems, found by reading the Si4684 datasheet
(AN649 Rev.2.0) instead of guessing further:

1. FM_RDS_CONFIG (property 0x3C02) was enabled (RDSEN=1) but with both
   block-error thresholds at 0 ("no block errors"), so almost any
   real-world RDS group -- routine with ordinary multipath/noise, even
   on a strong signal -- got rejected from the FIFO outright. Raised
   to the datasheet's most tolerant recommended setting (2, "3-5 bit
   errors detected and corrected").

2. FM_RDS_INTERRUPT_FIFO_COUNT (property 0x3C01) was never set at all,
   defaulting to 0 -- which the datasheet states disables RDSFIFOINT
   permanently. Si4684Driver::readFmRds()'s "received" flag reads
   exactly that bit (FM_RDS_STATUS RESP4 bit 0), so it could never be
   true, and Si4684Tuner::refreshStatus()'s RDS poll loop broke out on
   its first iteration every single time, before ever touching the
   accumulator. Set to 1 (fire as soon as one group is queued).

3. The real bug, once groups actually started arriving:
   RdsMetadataAccumulator::applyGroup() read the two Program Service
   name characters from Block C and computed the segment index as
   (blockB >> 1) & 0x3. Per ETSI EN 62106 §3.1.5, PS characters for
   group type 0 (both 0A and 0B) are always in Block D -- Block C
   holds alternate-frequency codes (0A) or a repeated PI code (0B),
   never text -- and the segment address is blockB bits[1:0] with no
   shift. This function had no dedicated test before now, which is
   how a wrong block/bit pair could ship unnoticed: the old test
   fixture encoded the same bug in its "expected" input.

Confirmed live after all three fixes: station_name and radiotext both
populate with stable, plausible content across repeated reads (not
noise) on a real broadcast signal.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
michele
2026-08-25 23:58:37 +02:00
co-authored by Claude Sonnet 5
parent 5d7d4919a0
commit d587032a0a
6 changed files with 168 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files
Software/components/core/src/RdsMetadataAccumulator.cpp
+7 -4
View File
@@ -35,12 +35,15 @@ void RdsMetadataAccumulator::applyGroup(std::uint16_t blockA,
static_cast<std::uint8_t>((blockB >> 12U) & 0x0FU);
if (groupType == 0U) {
const std::size_t index =
static_cast<std::size_t>((blockB >> 1U) & 0x03U);
// Group type 0 (both 0A and 0B): the two Program Service name
// characters are always in Block D. Block C differs by version --
// 0A carries alternate-frequency codes, 0B repeats the PI code --
// but never PS text either way (ETSI EN 62106 §3.1.5).
const std::size_t index = static_cast<std::size_t>(blockB & 0x03U);
if (index < kPsSegments) {
psBuffer_[index * 2U] =
static_cast<char>((blockC >> 8U) & 0xFFU);
psBuffer_[index * 2U + 1U] = static_cast<char>(blockC & 0xFFU);
static_cast<char>((blockD >> 8U) & 0xFFU);
psBuffer_[index * 2U + 1U] = static_cast<char>(blockD & 0xFFU);
psSegmentValid_[index] = true;
}
return;