From c4781e4203e37242b44a2cb9d5d1e41c4c9e6f47 Mon Sep 17 00:00:00 2001
From: Karl <klohner@users.noreply.github.com>
Date: Wed, 8 May 2024 18:20:26 -0400
Subject: [PATCH] ignore 3of6 decoding errors, let CRC fail decoding if
necessary, (#2883)
* ignore 3of6 decoding errors, let CRC fail decoding if necessary
* decode all 3of6 bytes, return count of contiguous bytes successfully decoded
* attempt decode all 3of6 bytes, return count of contiguously successful bytes
---
src/devices/m_bus.c | 42 +++++++++++++++++++++++-------------------
1 file changed, 23 insertions(+), 19 deletions(-)
diff --git a/src/devices/m_bus.c b/src/devices/m_bus.c
index ffa6562f..d9e0bb9f 100644
--- a/src/devices/m_bus.c
+++ b/src/devices/m_bus.c
@@ -31,25 +31,25 @@ static unsigned bcd2int(uint8_t bcd)
// Mapping from 6 bits to 4 bits. "3of6" coding used for Mode T
static uint8_t m_bus_decode_3of6(uint8_t byte)
{
- uint8_t out = 0xFF; // Error
+ uint8_t out = 0xF0; // Error
//fprintf(stderr,"Decode %0d\n", byte);
switch(byte) {
- case 22: out = 0x0; break; // 0x16
- case 13: out = 0x1; break; // 0x0D
- case 14: out = 0x2; break; // 0x0E
- case 11: out = 0x3; break; // 0x0B
- case 28: out = 0x4; break; // 0x17
- case 25: out = 0x5; break; // 0x19
- case 26: out = 0x6; break; // 0x1A
- case 19: out = 0x7; break; // 0x13
- case 44: out = 0x8; break; // 0x2C
- case 37: out = 0x9; break; // 0x25
- case 38: out = 0xA; break; // 0x26
- case 35: out = 0xB; break; // 0x23
- case 52: out = 0xC; break; // 0x34
- case 49: out = 0xD; break; // 0x31
- case 50: out = 0xE; break; // 0x32
- case 41: out = 0xF; break; // 0x29
+ case 22: out = 0x00; break; // 0x16
+ case 13: out = 0x01; break; // 0x0D
+ case 14: out = 0x02; break; // 0x0E
+ case 11: out = 0x03; break; // 0x0B
+ case 28: out = 0x04; break; // 0x1C
+ case 25: out = 0x05; break; // 0x19
+ case 26: out = 0x06; break; // 0x1A
+ case 19: out = 0x07; break; // 0x13
+ case 44: out = 0x08; break; // 0x2C
+ case 37: out = 0x09; break; // 0x25
+ case 38: out = 0x0A; break; // 0x26
+ case 35: out = 0x0B; break; // 0x23
+ case 52: out = 0x0C; break; // 0x34
+ case 49: out = 0x0D; break; // 0x31
+ case 50: out = 0x0E; break; // 0x32
+ case 41: out = 0x0F; break; // 0x29
default: break; // Error
}
return out;
@@ -59,15 +59,19 @@ static uint8_t m_bus_decode_3of6(uint8_t byte)
// Bad data must be handled with second layer CRC
static int m_bus_decode_3of6_buffer(uint8_t const *bits, unsigned bit_offset, uint8_t* output, unsigned num_bytes)
{
+ int successful_contiguous_bytes = -1;
for (unsigned n=0; n<num_bytes; ++n) {
uint8_t nibble_h = m_bus_decode_3of6(bitrow_get_byte(bits, n*12+bit_offset) >> 2);
uint8_t nibble_l = m_bus_decode_3of6(bitrow_get_byte(bits, n*12+bit_offset+6) >> 2);
if (nibble_h > 0xf || nibble_l > 0xf) {
- return -1;
+ // return -1; // fail at first 3of6 decoding error
+ nibble_l &= 0x0F; // assume logical 0 nibble if 3of6 decoding error, let CRC fail decoding if necessary
+ if (successful_contiguous_bytes < 0) successful_contiguous_bytes = n; // return count found until the first error
}
output[n] = (nibble_h << 4) | nibble_l;
}
- return 0;
+ if (successful_contiguous_bytes < 0) successful_contiguous_bytes = num_bytes; // if all data decoded successfully
+ return successful_contiguous_bytes;
}
// Validate CRC