/* Control protocol receiver sitting between 8b10b.c and logical protocol handlers */ #include #include "protocol.h" #include "8b10b.h" volatile uint32_t decoding_error_cnt = 0, protocol_error_cnt = 0; volatile bool backchannel_frame = 0; /* Reset the given protocol state and register the command definition given with it. */ void reset_receiver(struct proto_rx_st *st, const struct command_if_def *cmd_if) { st->rxpos = -1; st->address = 5; /* FIXME debug code */ st->cmd_if = cmd_if; } /* Receive an 8b10b symbol using the given protocol state. Handle any packets matching the enclosed command definition. * * This method is called from adc.c during the last bit period of the symbol, just before the actual end of the symbol * and start of the next symbol. */ void receive_symbol(struct proto_rx_st *st, int symbol) { if (symbol == -K28_2) { /* Backchannel marker */ /* This symbol is inserted into the symbol stream at regular intervals. It is not passed to the higher protocol * layers but synchronizes the backchannel logic through all nodes. The backchannel works by a node putting a * specified additional load of about 100mA (FIXME) on the line (1) or not (0) with all other nodes being * silent. The master can detect this additional current. The backchannel is synchronized to the 8b10b frame * being sent from the master, and the data is also 8b10b encoded. This means the backchannel is independent * from the forward-channel. * * This means while the forward-channel (the line voltage) might go like the upper trace, the back-channel (the * line current drawn by the node) might simultaneously look like the lower trace: * * Zoomed in on two master frames: * * |<--- D31.1 --->| |<--- D03.6 --->| * Master -> Node 1 0 1 0 1 1 1 0 0 1 1 1 0 0 0 1 0 1 1 0 * Voltage (V) .../^^\__/^^\__/^^^^^^^^\_____/^^^^^^^^\________/^^\__/^^^^^\___... * * Current (I) ...\_____________________________/^^^^^V^^^^^^^^V^^V^^V^^^^^V^^\... * Node -> Master 0 1 * * * Zoomed out on two node frames, or twenty master frames: * * Master -> Node | | | | | | | | | | | | | | | | | | |<- symbols, one after another * Voltage (V) ...XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX... * * Current (I) ...___/^^^^^\__/^^\_____/^^\__/^^^^^\_____/^^\__/^^^^^\__/^^\___... * Node -> Master 0 1 1 0 1 0 0 1 0 1 1 0 0 1 0 1 1 0 1 0 * |<--- D22.2 --->| |<--- D09.5 --->| * * Note that during backchannel transmissions only one node transmits at a time, and all nodes including the * transmitter keep their LEDs blanked to allow the master to more easily demodulate the transmission. * * This means that: * * backchannel transmissions should be sparse (one per several regular symbols) to not affect brightness * too much * * backchannel transmissions should be spaced-out evenly and frequent enough to not cause visible flicker * * A consequence of this is that the backchannel has a bandwidth of only a fraction of the forward-channel. The * master can dynamically adjust the frequency of the forward-channel and spacing of the backchannel markers. * For 5kHz and 10% backchannel data (every tenth symbol being a backchannel symbol) the bandwidth works out to: * * BW(forward-channel) = 5 [kHz] / 10 [8b10b] = 500 byte/s * BW(backchannel) = 5 [kHz] / 10 [8b10b] / 10 [every 10th symbol] / 10 [8b10b again] = 5 byte/s * * Luckily, we only use the backchannel for monitoring anyway and at ~20byte per monitoring frame we can easily * monitor a bus-load (heh!) of nodes once a minute, which is enough for our purposes. */ /* Blank the LEDs for the next frame to keep the bus quiet during backchannel transmission. This happens on all * nodes. */ backchannel_frame = true; return; /* We're done handling this symbol */ } else { /* On anything else than a backchannel marker, turn off backchannel blanking for the next frame */ backchannel_frame = false; } if (symbol == -K28_1) { /* Comma/frame delimiter */ st->rxpos = 0; /* Fall through and return and just ignore incomplete packets */ } else if (symbol == -DECODING_ERROR) { if (decoding_error_cnt < UINT32_MAX) decoding_error_cnt++; goto reset; } else if (symbol < 0) { /* Unknown comma symbol */ if (protocol_error_cnt < UINT32_MAX) protocol_error_cnt++; goto reset; } else if (st->rxpos == -1) { /* Receiver freshly reset and no comma seen yet */ return; } else if (st->rxpos == 0) { /* First data symbol, and not an error or comma symbol */ st->packet_type = symbol & ~PKT_TYPE_BULK_FLAG; if (st->packet_type >= st->cmd_if->packet_type_max) goto reset; /* Not a protocol error */ /* If this a bulk packet, calculate and store the offset of our portion of it. Otherwise just prime the state * for receiving the indidual packet by setting the offset to the first packet byte after the address. */ int payload_len = st->cmd_if->payload_len[st->packet_type]; st->is_bulk = symbol & PKT_TYPE_BULK_FLAG; st->offset = (st->is_bulk) ? (st->address*payload_len + 1) : 2; st->rxpos++; if (payload_len == 0 && st->is_bulk) { /* Length-0 packet type, handle now for bulk packets as we don't know when the master will send the next * comma or other symbol. For individually addressed packets, wait for the address byte. */ handle_command(st->packet_type, NULL); goto reset; } } else if (!st->is_bulk && st->rxpos == 1) { /* First byte (address byte) of individually adressed packet */ if (symbol != st->address) /* A different node is adressed */ goto reset; if (st->cmd_if->payload_len[st->packet_type] == 0) { /* Length-0 packet type, handle now as we don't know when the master will send the next comma or other * symbol. */ handle_command(st->packet_type, NULL); goto reset; } st->rxpos++; } else { /* Receiving packet body */ if (st->rxpos - st->offset >= 0) { /* Either we're receiving an individually adressed packet adressed to us, or we're in the middle of a bulk * packet at our offset */ st->argbuf[st->rxpos - st->offset] = symbol; } st->rxpos++; if (st->rxpos - st->offset == st->cmd_if->payload_len[st->packet_type]) { /* We're at the end of either an individual packet or our portion of a bulk packet. Handle packet here. */ handle_command(st->packet_type, (uint8_t *)st->argbuf); goto reset; } } return; reset: st->rxpos = -1; }