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Advanced Internet of Things firmware engineering with Thingsquare and Contiki - day 1, part 2
The Contiki netstack consists of four fixed layers - radio, duty cycling (RDC), MAC, and network. It uses a single packet buffer (packetbuf) to hold packets as they pass through each layer. Packetbuf attributes like addresses and RSSI are used to pass metadata between layers. Lower layers like MAC and radio use framers to convert between packet attributes and link-layer headers. When a packet is received, it moves up the stack from the radio layer through RDC, MAC, and network layers. When transmitting, it moves down the stack from network to MAC to RDC and radio.
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Advanced Internet of Things firmware engineering with Thingsquare and Contiki - day 1, part 2
- 1.
- 2. The Contiki netstack •Four layers – Network layer Application Transport Network, routing Adaptation – MAC layer – RDC layer – Radio layer MAC Duty cycling Radio
- 3. Netstack concepts • Fourfixed layers – – – – • • • • NETSTACK_RADIO NETSTACK_RDC NETSTACK_MAC NETSTACK_NETWORK The packet buffer – packetbuf Queue buffers – queuebuf uIP packet buffer – uip_buf Framers – NETSTACK_FRAMER
- 4. The packetbuf • Onebuffer, holds a single packet • All layers of the netstack operate on the packetbuf • Large enough to hold a single radio packet – PACKETBUF_CONF_LEN • Packet attributes – Parsed header data: addresses – Packet meta data: RSSI
- 5. The packetbuf hdrand data hdr data • hdr grows upwards – Only used on outbound path • data typically don’t grow – Contains data on outbound path – Contains header and data on inbound path
- 6. packetbuf • void packetbuf_clear(void); •int packetbuf_copyfrom(const void *from, uint16_t len); • void *packetbuf_dataptr(void); • uint16_t packetbuf_datalen(void); • void packetbuf_set_datalen(uint16_t len); • void *packetbuf_hdrptr(void); • uint8_t packetbuf_hdrlen(void); • uint16_t packetbuf_totlen(void); • void packetbuf_compact(void); • int packetbuf_copyto(void *to);
- 7. queuebuf • The packetbufonly holds the current packet • To store packets on queues, use a queuebuf • struct queuebuf *queuebuf_new_from_packetbuf(void); • void queuebuf_to_packetbuf(struct queuebuf *b); • void queuebuf_free(struct queuebuf *b); • Use a list to keep track of them
- 8. Framer • The framermodule converts link-layer headers to packet attributes – parse() • And packet attributes to link-layer headers – create()
- 9. Walking up thenetstack
- 10. A packet throughthe netstack • Step 1: the radio interrupt – Data arrives in bytes via an interrupt handler • Read byte by byte, put in buffer • Poll process on last byte – Or – Data arrives as a full packet via interrupt handler • Read out packet into buffer, poll process Application Transport Network, routing Adaptation MAC Duty cycling Radio
- 11. A packet throughthe netstack • Step 2: the radio process – Copy packet data from buffer into packetbuf – Read out RSSI, store as packetbuf attribute – Call NETSTACK_RDC.input(); Application Transport Network, routing Adaptation MAC Duty cycling Radio
- 12. Interruption: Calling Contikifrom an interrupt • The golden rule: there is only one safe Contiki function to call – process_poll(); • process_poll(&process) will cause the process to be sent a special PROCESS_EVENT_POLL event • Try to do as much as possible in a poll event handler • Synchronize data with ringbuf
- 13. A packet throughthe netstack • Step 3: the RDC input – Call framer to parse header – Check if pending bit set • Indicates a packet burst • Might need to have radio on for a while – Call NETSTACK_MAC.input() Application Transport Network, routing Adaptation MAC Duty cycling Radio
- 14. A packet throughthe netstack • Step 3: the MAC input – Just call NETSTACK_NETWORK.input() Application Transport Network, routing Adaptation MAC Duty cycling Radio
- 15. A packet throughthe netstack • Step 4: the 6lowpan input – Uncompress header – If part of a larger IPv6 packet, copy into fragmentation reassembly buffer and return to wait for the next packet – Copy packet into uip_buf – Call the IPv6 stack tcpip_input() Application Transport Network, routing Adaptation MAC Duty cycling Radio
- 16. Walking down thenetstack
- 17. A packet throughthe netstack • Step 1: the 6lowpan output – Clear packetbuf – Compress header from uip_buf to packetbuf – If uip_buf packet too large, split into several queuebufs – Call NETSTACK_MAC.send(); Application Transport Network, routing Adaptation MAC Duty cycling Radio
- 18. A packet throughthe netstack • Step 2: the MAC output – Find the receiver in the neighbor list – Add the packet to the neighbor’s output queue – If only packet on queue, call NETSTACK_RDC.send_list(); Application Transport Network, routing Adaptation MAC Duty cycling Radio
- 19. A packet throughthe netstack • Step 3: the RDC output – Check for radio traffic • If so, return a collision to the MAC layer – Send all packets on list, wait for ACK between each Application Transport Network, routing Adaptation MAC Duty cycling Radio
- 20. A packet throughthe netstack • Step 4: the radio output – Push packet to radio hardware – Send packet Application Transport Network, routing Adaptation MAC Duty cycling Radio
- 21.