Implement TDoA anchor protocol 2.0

[ataffanel]

The current TDoA protocol does not contain packet sequence number which makes it hard to verify TDoA integrity in case of lost packet on the tag side. A new TDoA protocol should then include packet sequence number.

Calculating the distance to other anchors and including it in the packet will also simplify a bit the tag implementation and could increase robustness to lost packet.

[ataffanel]

Proposed packet format:

typedef struct rangePacket_s {
  uint8_t type;
  uint8_t seqs[NSLOTS];  // Packet id of the timestamps
  uint8_t timestamps[NSLOTS][TS_TX_SIZE];  // Relevant time for anchors
  uint16_t distances[NSLOTS];
} __attribute__((packed)) rangePacket_t;

Assuming the current anchors is of ID anchor_id

• type is 0x22
• seqs[i]
  • If i == anchor_id Sequence number of the current packet
  • If i != anchor_id Sequence number of the latest receive packet from anchor i
• timestamps[i]
  • If i == anchor_id Transmit time of the current packet expressed in current anchor clock
  • If i != anchor_id Receive time of the latest receive packet from anchor i expressed in current anchor clock
• distances[i]
  • If i == anchor_id Reserved for future use
  • If i != anchor_id Time of flight between current anchor and anchor i in radio timer tick expressed in current anchor clock