diff options
Diffstat (limited to 'src/dabOutput/edi/PFT.cpp')
| -rw-r--r-- | src/dabOutput/edi/PFT.cpp | 109 |
1 files changed, 79 insertions, 30 deletions
diff --git a/src/dabOutput/edi/PFT.cpp b/src/dabOutput/edi/PFT.cpp index 5eaac09..4578392 100644 --- a/src/dabOutput/edi/PFT.cpp +++ b/src/dabOutput/edi/PFT.cpp @@ -41,52 +41,88 @@ using namespace std; -typedef vector<uint8_t> Chunk; +// An integer division that rounds up, i.e. ceil(a/b) +#define CEIL_DIV(a, b) (a % b == 0 ? a / b : a / b + 1) - -RSPacket PFT::Protect(AFPacket af_packet) +RSBlock PFT::Protect(AFPacket af_packet) { - RSPacket rs_packet; + RSBlock rs_block; // number of chunks is ceil(afpacketsize / m_k) - if (af_packet.size() % m_k == 0) { - m_num_chunks = af_packet.size() / m_k; - } - else { - m_num_chunks = af_packet.size() / m_k + 1; + // TS 102 821 7.2.2: c = ceil(l / k_max) + m_num_chunks = CEIL_DIV(af_packet.size(), 207); + + if (m_verbose) { + fprintf(stderr, "Protect %zu chunks of size %zu\n", + m_num_chunks, af_packet.size()); } - const size_t zero_pad = m_num_chunks * m_k - af_packet.size(); + // calculate size of chunk: + // TS 102 821 7.2.2: k = ceil(l / c) + // chunk_len does not include the 48 bytes of protection. + const size_t chunk_len = CEIL_DIV(af_packet.size(), m_num_chunks); + + // The last RS chunk is zero padded + // TS 102 821 7.2.2: z = c*k - l + const size_t zero_pad = m_num_chunks * chunk_len - af_packet.size(); + + // Create the RS(k+p,k) encoder + ReedSolomon rs_encoder(chunk_len + ParityBytes, chunk_len); // add zero padding to last chunk for (size_t i = 0; i < zero_pad; i++) { af_packet.push_back(0); } - for (size_t i = 1; i < af_packet.size(); i+= m_k) { - Chunk c(m_k + ParityBytes); + if (m_verbose) { + fprintf(stderr, " add %zu zero padding\n", zero_pad); + } + + // Calculate RS for each chunk and assemble RS block + for (size_t i = 0; i < af_packet.size(); i+= chunk_len) { + vector<uint8_t> chunk(chunk_len + ParityBytes); - // copy m_k bytes into new chunk - memcpy(&c.front(), &af_packet[i], m_k); + // copy chunk_len bytes into new chunk + memcpy(&chunk.front(), &af_packet[i], chunk_len); // calculate RS for chunk - m_encoder.encode(&c.front(), c.size()); + rs_encoder.encode(&chunk.front(), chunk.size()); // append new chunk to the RS Packet - rs_packet.insert(rs_packet.end(), c.begin(), c.end()); + rs_block.insert(rs_block.end(), chunk.begin(), chunk.end()); } - return rs_packet; + return rs_block; } vector< vector<uint8_t> > PFT::ProtectAndFragment(AFPacket af_packet) { - RSPacket rs_packet = Protect(af_packet); + RSBlock rs_block = Protect(af_packet); +#if 0 + fprintf(stderr, " af_packet (%zu):", af_packet.size()); + for (size_t i = 0; i < af_packet.size(); i++) { + fprintf(stderr, "%02x ", af_packet[i]); + } + fprintf(stderr, "\n"); + + fprintf(stderr, " rs_block (%zu):", rs_block.size()); + for (size_t i = 0; i < rs_block.size(); i++) { + fprintf(stderr, "%02x ", rs_block[i]); + } + fprintf(stderr, "\n"); +#endif + + // TS 102 821 7.2.2: s_max = MIN(floor(c*p/(m+1)), MTU - h)) const size_t max_payload_size = ( m_num_chunks * ParityBytes ) / (m_m + 1); - const size_t fragment_size = m_num_chunks * (m_k + ParityBytes) / max_payload_size; - const size_t num_fragments = m_num_chunks * (m_k + ParityBytes) / fragment_size; + // Calculate fragment count and size + // TS 102 821 7.2.2: ceil((l + c*p + z) / s_max) + // l + c*p + z = length of RS block + const size_t num_fragments = CEIL_DIV(rs_block.size(), max_payload_size); + + // TS 102 821 7.2.2: ceil((l + c*p + z) / f) + const size_t fragment_size = CEIL_DIV(rs_block.size(), num_fragments); if (m_verbose) fprintf(stderr, " PnF fragment_size %zu, num frag %zu\n", @@ -97,7 +133,12 @@ vector< vector<uint8_t> > PFT::ProtectAndFragment(AFPacket af_packet) for (size_t i = 0; i < num_fragments; i++) { fragments[i].resize(fragment_size); for (size_t j = 0; j < fragment_size; j++) { - fragments[i][j] = rs_packet[j*num_fragments + i]; + if (j*num_fragments + i > rs_block.size()) { + fragments[i][j] = 0; + } + else { + fragments[i][j] = rs_block[j*num_fragments + i]; + } } } @@ -107,13 +148,20 @@ vector< vector<uint8_t> > PFT::ProtectAndFragment(AFPacket af_packet) std::vector< PFTFragment > PFT::Assemble(AFPacket af_packet) { vector< vector<uint8_t> > fragments = ProtectAndFragment(af_packet); - vector< vector<uint8_t> > pft_fragments; + vector< vector<uint8_t> > pft_fragments; // These contain PF headers unsigned int findex = 0; unsigned fcount = fragments.size(); - const size_t zero_pad = m_num_chunks * m_k - af_packet.size(); + // calculate size of chunk: + // TS 102 821 7.2.2: k = ceil(l / c) + // chunk_len does not include the 48 bytes of protection. + const size_t chunk_len = CEIL_DIV(af_packet.size(), m_num_chunks); + + // The last RS chunk is zero padded + // TS 102 821 7.2.2: z = c*k - l + const size_t zero_pad = m_num_chunks * chunk_len - af_packet.size(); for (size_t i = 0; i < fragments.size(); i++) { const vector<uint8_t>& fragment = fragments[i]; @@ -136,11 +184,11 @@ std::vector< PFTFragment > PFT::Assemble(AFPacket af_packet) unsigned int plen = fragment.size(); plen |= 0x8000; // Set FEC bit - packet.push_back(plen >> 8); // RSk - packet.push_back(plen & 0xFF); // RSz + packet.push_back(plen >> 8); + packet.push_back(plen & 0xFF); - packet.push_back(m_k); - packet.push_back(zero_pad); + packet.push_back(chunk_len); // RSk + packet.push_back(zero_pad); // RSz // calculate CRC over AF Header and payload uint16_t crc = 0xffff; @@ -155,9 +203,10 @@ std::vector< PFTFragment > PFT::Assemble(AFPacket af_packet) pft_fragments.push_back(packet); - if (m_verbose) - fprintf(stderr, "* PFT pseq %d, findex %d, fcount %d, plen %d\n", - m_pseq, findex, fcount, plen & ~0x8000); +#if 0 + fprintf(stderr, "* PFT pseq %d, findex %d, fcount %d, plen %d\n", + m_pseq, findex, fcount, plen & ~0x8000); +#endif } m_pseq++; |