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Support Rate 1/2 Data CRC Mask

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The previous implementation hardcoded the mask for Rate 3/4 Data (0x01ff),
causing CRC check failure for Rate 1/2 on both encode and decode.

This patch also refactors to avoid code copying and fixes a bug where
calling DataBlock.Byte() on the output of Fragment.DataBlocks() produced
an incorrect CRC value due to Bytes() not resetting db.CRC before
performing it's own CRC calculation.
This commit is contained in:
Martin Hebnes Pedersen 2019-05-07 22:38:24 +02:00
parent 2851102398
commit 29c24593f9
1 changed files with 27 additions and 34 deletions
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61
data.go
View file

@ -15,6 +15,30 @@ const (
MaxPacketFragmentSize = 1500
)
// CRC Masks for data block's CRC-9 calculation, see DMR AI spec. page 148 (Table B.21).
var crc9Masks = map[uint8]uint16{
Rate12Data: 0x00f0,
Rate34Data: 0x01ff,
//Rate1Data: 0x010f,
}
func calculateCRC9(serial uint8, data []byte, dataType uint8) (crc uint16) {
for _, block := range data {
crc9(&crc, block, 8)
}
crc9(&crc, serial, 7)
crc9end(&crc, 8)
// Inverting according to the inversion polynomial.
crc = ^crc
crc &= 0x01ff
// Applying Data Type CRC Mask
crc ^= crc9Masks[dataType]
return crc
}
type DataBlock struct {
Serial uint8
CRC uint16
@ -37,17 +61,7 @@ func ParseDataBlock(data []byte, dataType uint8, confirmed bool) (*DataBlock, er
db.Data = make([]byte, db.Length)
copy(db.Data, data[2:2+db.Length])
for _, block := range db.Data {
crc9(&crc, block, 8)
}
crc9(&crc, db.Serial, 7)
crc9end(&crc, 8)
// Inverting according to the inversion polynomial.
crc = ^crc
crc &= 0x01ff
// Applying CRC mask, see DMR AI spec. page 143
crc ^= 0x01ff
crc = calculateCRC9(db.Serial, db.Data, dataType)
// FIXME(pd0mz): this is not working
if crc != db.CRC {
@ -69,17 +83,7 @@ func (db *DataBlock) Bytes(dataType uint8, confirmed bool) []byte {
)
if confirmed {
for _, block := range db.Data {
crc9(&db.CRC, block, 8)
}
crc9(&db.CRC, db.Serial, 7)
crc9end(&db.CRC, 8)
// Inverting according to the inversion polynomial.
db.CRC = ^db.CRC
db.CRC &= 0x01ff
// Applying CRC mask, see DMR AI spec. page 143
db.CRC ^= 0x01ff
db.CRC = calculateCRC9(db.Serial, db.Data, dataType)
// Grow data slice to support the two byte prefix
data = append(data, make([]byte, 2)...)
@ -180,18 +184,7 @@ func (df *DataFragment) DataBlocks(dataType uint8, confirm bool) ([]*DataBlock,
}
// Calculate block CRC9
block.CRC = 0
for _, b := range block.Data {
crc9(&block.CRC, b, 8)
}
crc9(&block.CRC, block.Serial, 7)
crc9end(&block.CRC, 8)
// Inverting according to the inversion polynomial
block.CRC = ^block.CRC
block.CRC &= 0x01ff
// Applying CRC mask, see DMR AI spec. page 143
block.CRC ^= 0x01ff
block.CRC = calculateCRC9(block.Serial, block.Data, dataType)
blocks[i] = block
}