diff options
Diffstat (limited to 'center_fw/src/protocol.c')
| -rw-r--r-- | center_fw/src/protocol.c | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/center_fw/src/protocol.c b/center_fw/src/protocol.c new file mode 100644 index 0000000..dfa0d3e --- /dev/null +++ b/center_fw/src/protocol.c @@ -0,0 +1,149 @@ +/* Control protocol receiver sitting between 8b10b.c and logical protocol handlers */ + +#include <unistd.h> +#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; +} + |