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fix: Update CRC calc to use 0 init and full 16-bit stored value
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Daniel Dybing
2026-02-07 10:47:29 +01:00
parent 6a6df63980
commit 84d1094d16
1 changed files with 5 additions and 4 deletions
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9
src/teletext/models.py
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@@ -82,8 +82,9 @@ class Page:
Row 0: Skips first 8 bytes (Header/Control). Uses bytes 8-39. Row 0: Skips first 8 bytes (Header/Control). Uses bytes 8-39.
Rows 1-23: Uses all 40 bytes. Rows 1-23: Uses all 40 bytes.
Data is 7-bit (stripped parity). Data is 7-bit (stripped parity).
Initial value: 0 (ETSI EN 300 706 9.4.1.2).
""" """
crc = 0xFFFF crc = 0
poly = 0x1021 poly = 0x1021
# Helper to update CRC with a byte # Helper to update CRC with a byte
@@ -135,13 +136,13 @@ class Page:
if designation == 0: if designation == 0:
# Packet 27/0 # Packet 27/0
# Checksum is in bytes 38 and 39 # Checksum is in bytes 38 and 39.
# ETSI EN 300 706: 8 bits of each byte are used.
if len(p.data) >= 40: if len(p.data) >= 40:
hi = p.data[38] hi = p.data[38]
lo = p.data[39] lo = p.data[39]
# Strip parity crc = (hi << 8) | lo
crc = ((hi & 0x7F) << 8) | (lo & 0x7F)
return crc return crc
except: except:
pass pass