Revision 0:80dd1516ad46, committed 2015-03-18

Comitter:

dnleek

Date:

Wed Mar 18 07:59:36 2015 +0000

Commit message:

Telemetry library from ducky

Changed in this revision

diff -r 000000000000 -r 80dd1516ad46 telemetry-data.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/telemetry-data.cpp	Wed Mar 18 07:59:36 2015 +0000
@@ -0,0 +1,90 @@
+/*
+ * telemetry-data.cpp
+ *
+ *  Created on: Mar 2, 2015
+ *      Author: Ducky
+ *
+ * Implementation for Telemetry Data classes.
+ */
+#include <telemetry.h>
+#include <string.h>
+
+namespace telemetry {
+void packet_write_string(TransmitPacketInterface& packet, const char* str) {
+  // TODO: move into HAL for higher performance?
+  while (*str != '\0') {
+    packet.write_uint8(*str);
+    str++;
+  }
+  packet.write_uint8('\0');
+}
+
+size_t Data::get_header_kvrs_length() {
+  return 1 + strlen(internal_name) + 1
+      + 1 + strlen(display_name) + 1
+      + 1 + strlen(units) + 1;
+}
+
+void Data::write_header_kvrs(TransmitPacketInterface& packet) {
+  packet.write_uint8(RECORDID_INTERNAL_NAME);
+  packet_write_string(packet, internal_name);
+  packet.write_uint8(RECORDID_DISPLAY_NAME);
+  packet_write_string(packet, display_name);
+  packet.write_uint8(RECORDID_UNITS);
+  packet_write_string(packet, units);
+}
+
+template<>
+uint8_t Numeric<uint8_t>::get_subtype() {
+  return NUMERIC_SUBTYPE_UINT;
+}
+template<>
+void Numeric<uint8_t>::serialize_data(uint8_t value, TransmitPacketInterface& packet) {
+  packet.write_uint8(value);
+}
+template<>
+uint8_t Numeric<uint8_t>::deserialize_data(ReceivePacketBuffer& packet) {
+  return packet.read_uint8();
+}
+
+template<>
+uint8_t Numeric<uint16_t>::get_subtype() {
+  return NUMERIC_SUBTYPE_UINT;
+}
+template<>
+void Numeric<uint16_t>::serialize_data(uint16_t value, TransmitPacketInterface& packet) {
+  packet.write_uint16(value);
+}
+template<>
+uint16_t Numeric<uint16_t>::deserialize_data(ReceivePacketBuffer& packet) {
+  return packet.read_uint16();
+}
+
+template<>
+uint8_t Numeric<uint32_t>::get_subtype() {
+  return NUMERIC_SUBTYPE_UINT;
+}
+template<>
+void Numeric<uint32_t>::serialize_data(uint32_t value, TransmitPacketInterface& packet) {
+  packet.write_uint32(value);
+}
+template<>
+uint32_t Numeric<uint32_t>::deserialize_data(ReceivePacketBuffer& packet) {
+  return packet.read_uint32();
+}
+
+// TODO: move into HAL
+template<>
+uint8_t Numeric<float>::get_subtype() {
+  return NUMERIC_SUBTYPE_FLOAT;
+}
+template<>
+void Numeric<float>::serialize_data(float value, TransmitPacketInterface& packet) {
+  packet.write_float(value);
+}
+template<>
+float Numeric<float>::deserialize_data(ReceivePacketBuffer& packet) {
+  return packet.read_float();
+}
+
+}

diff -r 000000000000 -r 80dd1516ad46 telemetry-mbed-hal.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/telemetry-mbed-hal.cpp	Wed Mar 18 07:59:36 2015 +0000
@@ -0,0 +1,39 @@
+/*
+ * telemetry-mbedo-hal.cpp
+ *
+ *  Created on: Mar 4, 2015
+ *      Author: Ducky
+ *
+ * Telemetry HAL for Serial on mBed.
+ */
+
+#ifdef __ARMCC_VERSION
+
+#include "telemetry-mbed.h"
+
+namespace telemetry {
+
+void MbedHal::transmit_byte(uint8_t data) {
+  // TODO: optimize with DMA
+  serial.putc(data);
+}
+
+size_t MbedHal::rx_available() {
+  return serial.rxBufferGetCount();
+}
+
+uint8_t MbedHal::receive_byte() {
+  return serial.getc();
+}
+
+void MbedHal::do_error(const char* msg) {
+  serial.printf("%s\r\n", msg);
+}
+
+uint32_t MbedHal::get_time_ms() {
+  return timer.read_ms();
+}
+
+}
+
+#endif // ifdef MBED

diff -r 000000000000 -r 80dd1516ad46 telemetry-mbed.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/telemetry-mbed.h	Wed Mar 18 07:59:36 2015 +0000
@@ -0,0 +1,32 @@
+// Make this less hacky and detect properly
+#ifdef __ARMCC_VERSION
+
+#include "telemetry.h"
+#include "mbed.h"
+#include "MODSERIAL.h"
+
+namespace telemetry {
+
+class MbedHal : public HalInterface {
+public:
+  MbedHal(MODSERIAL& serial) :
+    serial(serial) {
+	  timer.start();
+  }
+
+  virtual void transmit_byte(uint8_t data);
+  virtual size_t rx_available();
+  virtual uint8_t receive_byte();
+
+  virtual void do_error(const char* message);
+
+  virtual uint32_t get_time_ms();
+
+protected:
+  MODSERIAL& serial;
+  Timer timer;
+};
+
+}
+
+#endif // ifdef MBED

diff -r 000000000000 -r 80dd1516ad46 telemetry.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/telemetry.cpp	Wed Mar 18 07:59:36 2015 +0000
@@ -0,0 +1,332 @@
+/*
+ * telemetry.cpp
+ *
+ *  Created on: Mar 2, 2015
+ *      Author: Ducky
+ *
+ * Implementation for the base Telemetry class.
+ */
+
+#include <telemetry.h>
+
+namespace telemetry {
+
+size_t Telemetry::add_data(Data& new_data) {
+  if (data_count >= MAX_DATA_PER_TELEMETRY) {
+    do_error("MAX_DATA_PER_TELEMETRY limit reached.");
+    return 0;
+  }
+  if (header_transmitted) {
+    do_error("Cannot add new data after header transmitted.");
+    return 0;
+  }
+  data[data_count] = &new_data;
+  data_updated[data_count] = true;
+  data_count++;
+  return data_count - 1;
+}
+
+void Telemetry::mark_data_updated(size_t data_id) {
+  data_updated[data_id] = true;
+}
+
+void Telemetry::transmit_header() {
+  if (header_transmitted) {
+    do_error("Cannot retransmit header.");
+    return;
+  }
+
+  size_t packet_legnth = 2; // opcode + sequence
+  for (int data_idx = 0; data_idx < data_count; data_idx++) {
+    packet_legnth += 2; // data ID, data type
+    packet_legnth += data[data_idx]->get_header_kvrs_length();
+    packet_legnth += 1; // terminator record id
+  }
+  packet_legnth++;  // terminator "record"
+
+  FixedLengthTransmitPacket packet(hal, packet_legnth);
+
+  packet.write_uint8(OPCODE_HEADER);
+  packet.write_uint8(packet_tx_sequence);
+  for (int data_idx = 0; data_idx < data_count; data_idx++) {
+    packet.write_uint8(data_idx+1);
+    packet.write_uint8(data[data_idx]->get_data_type());
+    data[data_idx]->write_header_kvrs(packet);
+    packet.write_uint8(RECORDID_TERMINATOR);
+  }
+  packet.write_uint8(DATAID_TERMINATOR);
+
+  packet.finish();
+
+  packet_tx_sequence++;
+  header_transmitted = true;
+}
+
+void Telemetry::do_io() {
+  transmit_data();
+  process_received_data();
+}
+
+void Telemetry::transmit_data() {
+  if (!header_transmitted) {
+    do_error("Must transmit header before transmitting data.");
+    return;
+  }
+
+  // Keep a local copy to make it more thread-safe
+  bool data_updated_local[MAX_DATA_PER_TELEMETRY];
+
+  size_t packet_legnth = 2; // opcode + sequence
+  for (int data_idx = 0; data_idx < data_count; data_idx++) {
+    data_updated_local[data_idx] = data_updated[data_idx];
+    data_updated[data_idx] = 0;
+    if (data_updated_local[data_idx]) {
+      packet_legnth += 1; // data ID
+      packet_legnth += data[data_idx]->get_payload_length();
+    }
+  }
+  packet_legnth++;  // terminator "record"
+
+  FixedLengthTransmitPacket packet(hal, packet_legnth);
+
+  packet.write_uint8(OPCODE_DATA);
+  packet.write_uint8(packet_tx_sequence);
+  for (int data_idx = 0; data_idx < data_count; data_idx++) {
+    if (data_updated_local[data_idx]) {
+      packet.write_uint8(data_idx+1);
+      data[data_idx]->write_payload(packet);
+    }
+  }
+  packet.write_uint8(DATAID_TERMINATOR);
+
+  packet.finish();
+
+  packet_tx_sequence++;
+}
+
+void Telemetry::process_received_data() {
+  uint32_t current_time = hal.get_time_ms();
+
+  if (decoder_last_receive_ms <= current_time) {
+	if (!decoder_last_received && decoder_state != SOF && decoder_pos != 0
+		&& (decoder_last_receive_ms - current_time > DECODER_TIMEOUT_MS)) {
+	  decoder_pos = 0;
+	  packet_length = 0;
+	  decoder_state = SOF;
+	  hal.do_error("RX timeout");
+	}
+  } else {
+	// timer overflowed, do nothing
+  }
+  decoder_last_receive_ms = current_time;
+
+  decoder_last_received = false;
+  while (hal.rx_available()) {
+	decoder_last_received = true;
+
+    uint8_t rx_byte = hal.receive_byte();
+
+    if (decoder_state == SOF) {
+      if (rx_byte == SOF_SEQ[decoder_pos]) {
+        decoder_pos++;
+        if (decoder_pos >= (sizeof(SOF_SEQ) / sizeof(SOF_SEQ[0]))) {
+          decoder_pos = 0;
+          packet_length = 0;
+          decoder_state = LENGTH;
+        }
+      } else {
+        decoder_pos = 0;
+        // TODO: pass rest of data through
+      }
+    } else if (decoder_state == LENGTH) {
+      packet_length = (packet_length << 8) | rx_byte;
+      decoder_pos++;
+      if (decoder_pos >= LENGTH_SIZE) {
+        decoder_pos = 0;
+        decoder_state = DATA;
+      }
+    } else if (decoder_state == DATA) {
+      received_packet.add_byte(rx_byte);
+      decoder_pos++;
+      if (decoder_pos >= packet_length) {
+        process_received_packet();
+
+        decoder_pos = 0;
+        if (rx_byte == SOF_SEQ[0]) {
+          decoder_state = DATA_DESTUFF_END;
+        } else {
+          decoder_state = SOF;
+        }
+      } else {
+        if (rx_byte == SOF_SEQ[0]) {
+          decoder_state = DATA_DESTUFF;
+        }
+      }
+    } else if (decoder_state == DATA_DESTUFF) {
+      decoder_state = DATA;
+    } else if (decoder_state == DATA_DESTUFF_END) {
+      decoder_state = SOF;
+    }
+  }
+}
+
+void Telemetry::process_received_packet() {
+  uint8_t opcode = received_packet.read_uint8();
+  if (opcode == OPCODE_DATA) {
+    uint8_t data_id = received_packet.read_uint8();
+    while (data_id != DATAID_TERMINATOR) {
+      if (data_id < data_count + 1) {
+        data[data_id - 1]->set_from_packet(received_packet);
+      } else {
+        hal.do_error("Unknown data ID");
+      }
+      data_id = received_packet.read_uint8();
+    }
+  } else {
+    hal.do_error("Unknown opcode");
+  }
+}
+
+size_t Telemetry::receive_available() {
+  // TODO: implement me
+  return 0;
+}
+
+uint8_t read_receive() {
+  // TODO: implement me
+  return 0;
+}
+
+FixedLengthTransmitPacket::FixedLengthTransmitPacket(HalInterface& hal,
+    size_t length) :
+        hal(hal),
+        length(length),
+        count(0) {
+  hal.transmit_byte(SOF1);
+  hal.transmit_byte(SOF2);
+
+  hal.transmit_byte((length >> 8) & 0xff);
+  hal.transmit_byte((length >> 0) & 0xff);
+
+  valid = true;
+}
+
+void FixedLengthTransmitPacket::write_byte(uint8_t data) {
+  if (!valid) {
+    hal.do_error("Writing to invalid packet");
+    return;
+  } else if (count + 1 > length) {
+    hal.do_error("Writing over packet length");
+    return;
+  }
+  hal.transmit_byte(data);
+  if (data == SOF1) {
+    hal.transmit_byte(0x00);  // TODO: proper abstraction and magic numbers
+  }
+  count++;
+}
+
+void FixedLengthTransmitPacket::write_uint8(uint8_t data) {
+  write_byte(data);
+}
+
+void FixedLengthTransmitPacket::write_uint16(uint16_t data) {
+  write_byte((data >> 8) & 0xff);
+  write_byte((data >> 0) & 0xff);
+}
+
+void FixedLengthTransmitPacket::write_uint32(uint32_t data) {
+  write_byte((data >> 24) & 0xff);
+  write_byte((data >> 16) & 0xff);
+  write_byte((data >> 8) & 0xff);
+  write_byte((data >> 0) & 0xff);
+}
+
+void FixedLengthTransmitPacket::write_float(float data) {
+  // TODO: THIS IS ENDIANNESS DEPENDENT, ABSTRACT INTO HAL?
+  uint8_t *float_array = (uint8_t*) &data;
+  write_byte(float_array[3]);
+  write_byte(float_array[2]);
+  write_byte(float_array[1]);
+  write_byte(float_array[0]);
+}
+
+void FixedLengthTransmitPacket::finish() {
+  if (!valid) {
+    hal.do_error("Finish invalid packet");
+    return;
+  } else if (count != length) {
+    hal.do_error("TX packet under length");
+    return;
+  }
+
+  // TODO: add CRC check here
+}
+
+ReceivePacketBuffer::ReceivePacketBuffer(HalInterface& hal) :
+    hal(hal) {
+  new_packet();
+}
+
+void ReceivePacketBuffer::new_packet() {
+  packet_length = 0;
+  read_loc = 0;
+}
+
+void ReceivePacketBuffer::add_byte(uint8_t byte) {
+  if (packet_length >= MAX_RECEIVE_PACKET_LENGTH) {
+    hal.do_error("RX packet over length");
+    return;
+  }
+
+  data[packet_length] = byte;
+  packet_length++;
+}
+
+uint8_t ReceivePacketBuffer::read_uint8() {
+  if (read_loc + 1 > packet_length) {
+    hal.do_error("Read uint8 over length");
+    return 0;
+  }
+  read_loc += 1;
+  return data[read_loc - 1];
+}
+
+uint16_t ReceivePacketBuffer::read_uint16() {
+  if (read_loc + 2 > packet_length) {
+    hal.do_error("Read uint16 over length");
+    return 0;
+  }
+  read_loc += 2;
+  return ((uint16_t)data[read_loc - 2] << 8)
+       | ((uint16_t)data[read_loc - 1] << 0);
+}
+
+uint32_t ReceivePacketBuffer::read_uint32() {
+  if (read_loc + 4 > packet_length) {
+    hal.do_error("Read uint32 over length");
+    return 0;
+  }
+  read_loc += 4;
+  return ((uint32_t)data[read_loc - 4] << 24)
+       | ((uint32_t)data[read_loc - 3] << 16)
+       | ((uint32_t)data[read_loc - 2] << 8)
+       | ((uint32_t)data[read_loc - 1] << 0);
+}
+
+float ReceivePacketBuffer::read_float() {
+  if (read_loc + 4 > packet_length) {
+    hal.do_error("Read float over length");
+    return 0;
+  }
+  read_loc += 4;
+  float out = 0;
+  uint8_t* out_array = (uint8_t*)&out;
+  out_array[0] = data[read_loc - 1];
+  out_array[1] = data[read_loc - 2];
+  out_array[2] = data[read_loc - 3];
+  out_array[3] = data[read_loc - 4];
+  return out;
+}
+
+}

diff -r 000000000000 -r 80dd1516ad46 telemetry.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/telemetry.h	Wed Mar 18 07:59:36 2015 +0000
@@ -0,0 +1,524 @@
+#ifndef _TELEMETRY_H_
+#define _TELEMETRY_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+namespace telemetry {
+
+#ifndef TELEMETRY_DATA_LIMIT
+#define TELEMETRY_DATA_LIMIT 16
+#endif
+
+// Maximum number of DataInterface objects a Telemetry object can hold.
+// Used for array sizing.
+const size_t MAX_DATA_PER_TELEMETRY = TELEMETRY_DATA_LIMIT;
+
+// Maximum payload size for a received telemetry packet.
+const size_t MAX_RECEIVE_PACKET_LENGTH = 255;
+
+// Various wire protocol constants.
+const uint8_t SOF1 = 0x05;  // start of frame byte 1
+const uint8_t SOF2 = 0x39;  // start of frame byte 2
+const uint8_t SOF_SEQ[] = {0x05, 0x39};
+
+const size_t LENGTH_SIZE = 2;
+
+// TODO: make these length independent
+
+const uint8_t OPCODE_HEADER = 0x81;
+const uint8_t OPCODE_DATA = 0x01;
+
+const uint8_t DATAID_TERMINATOR = 0x00;
+
+const uint8_t DATATYPE_NUMERIC = 0x01;
+const uint8_t DATATYPE_NUMERIC_ARRAY = 0x02;
+
+const uint8_t RECORDID_TERMINATOR = 0x00;
+const uint8_t RECORDID_INTERNAL_NAME = 0x01;
+const uint8_t RECORDID_DISPLAY_NAME = 0x02;
+const uint8_t RECORDID_UNITS = 0x03;
+
+const uint8_t RECORDID_OVERRIDE_CTL = 0x08;
+const uint8_t RECORDID_OVERRIDE_DATA = 0x08;
+
+const uint8_t RECORDID_NUMERIC_SUBTYPE = 0x40;
+const uint8_t RECORDID_NUMERIC_LENGTH = 0x41;
+const uint8_t RECORDID_NUMERIC_LIMITS = 0x42;
+const uint8_t RECORDID_ARRAY_COUNT = 0x50;
+
+const uint8_t NUMERIC_SUBTYPE_UINT = 0x01;
+const uint8_t NUMERIC_SUBTYPE_SINT = 0x02;
+const uint8_t NUMERIC_SUBTYPE_FLOAT = 0x03;
+
+const uint32_t DECODER_TIMEOUT_MS = 100;
+
+// Hardware abstraction layer for the telemetry server.
+class HalInterface {
+public:
+  virtual ~HalInterface() {}
+
+  // Write a byte to the transmit buffer.
+  virtual void transmit_byte(uint8_t data) = 0;
+  // Returns the number of bytes available in the receive buffer.
+  virtual size_t rx_available() = 0;
+  // Returns the next byte in the receive stream. rx_available must return > 0.
+  virtual uint8_t receive_byte() = 0;
+
+  // TODO: more efficient block transmit operations?
+
+  // Called on a telemetry error.
+  virtual void do_error(const char* message) = 0;
+
+  // Return the current time in milliseconds. May overflow at any time.
+  virtual uint32_t get_time_ms() = 0;
+};
+
+// Abstract base class for building a packet to be transmitted.
+// Implementation is unconstrained - writes may either be buffered or passed
+// directly to the hardware transmit buffers.
+class TransmitPacketInterface {
+public:
+  virtual ~TransmitPacketInterface() {}
+
+  // Writes a 8-bit unsigned integer to the packet stream.
+  virtual void write_byte(uint8_t data) = 0;
+    
+  // Writes a 8-bit unsigned integer to the packet stream.
+  virtual void write_uint8(uint8_t data) = 0;
+  // Writes a 16-bit unsigned integer to the packet stream.
+  virtual void write_uint16(uint16_t data) = 0;
+  // Writes a 32-bit unsigned integer to the packet stream.
+  virtual void write_uint32(uint32_t data) = 0;
+  // Writes a float to the packet stream.
+  virtual void write_float(float data) = 0;
+
+  // Finish the packet and writes data to the transmit stream (if not already
+  // done). No more data may be written afterwards.
+  virtual void finish() = 0;
+};
+
+class ReceivePacketBuffer {
+public:
+  ReceivePacketBuffer(HalInterface& hal);
+
+  // Starts a new packet, resetting the packet length and read pointer.
+  void new_packet();
+
+  // Appends a new byte onto this packet, advancing the packet length
+  void add_byte(uint8_t byte);
+
+  // Reads a 8-bit unsigned integer from the packet stream, advancing buffer.
+  uint8_t read_uint8();
+  // Reads a 16-bit unsigned integer from the packet stream, advancing buffer.
+  uint16_t read_uint16();
+  // Reads a 32-bit unsigned integer from the packet stream, advancing buffer.
+  uint32_t read_uint32();
+  // Reads a float from the packet stream, advancing buffer.
+  float read_float();
+
+protected:
+  HalInterface& hal;
+
+  size_t packet_length;
+  size_t read_loc;
+  uint8_t data[MAX_RECEIVE_PACKET_LENGTH];
+};
+
+// Abstract base class for telemetry data objects.
+class Data {
+public:
+  Data(const char* internal_name, const char* display_name,
+      const char* units):
+      internal_name(internal_name),
+      display_name(display_name),
+      units(units) {};
+
+  virtual ~Data() {}
+
+  // Returns the data type code.
+  virtual uint8_t get_data_type() = 0;
+
+  // Returns the length of the header KVRs, in bytes. Does not include the
+  // terminator header.
+  virtual size_t get_header_kvrs_length();
+  // Writes the header KVRs to the transmit packet. Does not write the
+  // terminiator header.
+  virtual void write_header_kvrs(TransmitPacketInterface& packet);
+
+  // Returns the length of the payload, in bytes. Should be "fast".
+  virtual size_t get_payload_length() = 0;
+  // Writes the payload to the transmit packet. Should be "fast".
+  virtual void write_payload(TransmitPacketInterface& packet) = 0;
+
+  // Sets my value from the received packet, interpreting the current packet
+  // read position as my data type.
+  virtual void set_from_packet(ReceivePacketBuffer& packet) = 0;
+
+protected:
+  const char* internal_name;
+  const char* display_name;
+  const char* units;
+};
+
+// Telemetry Server object.
+class Telemetry {
+public:
+  Telemetry(HalInterface& hal) :
+    hal(hal),
+    data_count(0),
+    received_packet(ReceivePacketBuffer(hal)),
+    decoder_state(SOF),
+    decoder_pos(0),
+    packet_length(0),
+	decoder_last_received(false),
+	decoder_last_receive_ms(0),
+    header_transmitted(false),
+    packet_tx_sequence(0),
+    packet_rx_sequence(0) {};
+
+  // Associates a DataInterface with this object, returning the data ID.
+  size_t add_data(Data& new_data);
+
+  // Marks a data ID as updated, to be transmitted in the next packet.
+  void mark_data_updated(size_t data_id);
+
+  // Transmits header data. Must be called after all add_data calls are done
+  // and before and IO is done.
+  void transmit_header();
+
+  // Does IO, including transmitting telemetry packets. Should be called on
+  // a regular basis. Since this does IO, this may block depending on the HAL
+  // semantics.
+  void do_io();
+
+  // TODO: better docs defining in-band receive.
+  // Returns the number of bytes available in the receive stream.
+  size_t receive_available();
+  // Returns the next byte in the receive stream.
+  uint8_t read_receive();
+
+  // Calls the HAL's error function if some condition is false.
+  void do_error(const char* message) {
+    hal.do_error(message);
+  }
+
+protected:
+  // Transmits any updated data.
+  void transmit_data();
+
+  // Handles received data, splitting regular UART data from in-band packet
+  // data and processing received telemetry packets.
+  void process_received_data();
+
+  // Handles a received packet in received_packet.
+  void process_received_packet();
+
+  HalInterface& hal;
+
+  // Array of associated DataInterface objects. The index+1 is the
+  // DataInterface's data ID field.
+  Data* data[MAX_DATA_PER_TELEMETRY];
+  // Whether each data has been updated or not.
+  bool data_updated[MAX_DATA_PER_TELEMETRY];
+  // Count of associated DataInterface objects.
+  size_t data_count;
+
+  // Buffer holding the receive packet being assembled / parsed.
+  ReceivePacketBuffer received_packet;
+
+  enum DecoderState {
+    SOF,    // reading start-of-frame sequence (or just non-telemetry data)
+    LENGTH, // reading packet length
+    DATA,   // reading telemetry packet data
+    DATA_DESTUFF,     // reading a stuffed byte
+    DATA_DESTUFF_END  // last stuffed byte in a packet
+  } decoder_state;
+
+  size_t decoder_pos;
+  size_t packet_length;
+  bool decoder_last_received;
+  uint32_t decoder_last_receive_ms;
+
+  bool header_transmitted;
+
+  // Sequence number of the next packet to be transmitted.
+  uint8_t packet_tx_sequence;
+  uint8_t packet_rx_sequence; // TODO use this somewhere
+};
+
+// A telemetry packet with a length known before data is written to it.
+// Data is written directly to the hardware transmit buffers without packet
+// buffering. Assumes transmit buffers won't fill up.
+class FixedLengthTransmitPacket : public TransmitPacketInterface {
+public:
+  FixedLengthTransmitPacket(HalInterface& hal, size_t length);
+
+  virtual void write_byte(uint8_t data);
+
+  virtual void write_uint8(uint8_t data);
+  virtual void write_uint16(uint16_t data);
+  virtual void write_uint32(uint32_t data);
+  virtual void write_float(float data);
+
+  virtual void finish();
+
+protected:
+  HalInterface& hal;
+
+  // Predetermined length, in bytes, of this packet's payload, for sanity check.
+  size_t length;
+
+  // Current length, in bytes, of this packet's payload.
+  size_t count;
+
+  // Is the packet valid?
+  bool valid;
+};
+
+template <typename T> 
+class Numeric : public Data {
+public:
+  Numeric(Telemetry& telemetry_container, 
+      const char* internal_name, const char* display_name,
+      const char* units, T init_value):
+      Data(internal_name, display_name, units),
+      telemetry_container(telemetry_container),
+      value(init_value), min_val(init_value), max_val(init_value),
+      frozen(false) {
+    data_id = telemetry_container.add_data(*this);
+  }
+
+  T operator = (T b) {
+    if (!frozen) {
+      value = b;
+      telemetry_container.mark_data_updated(data_id);
+    }
+    return value;
+  }
+
+  operator T() {
+    return value;
+  }
+  
+  Numeric<T>& set_limits(T min, T max) {
+    min_val = min;
+    max_val = max;
+    return *this;
+  }
+  
+  virtual uint8_t get_data_type() { return DATATYPE_NUMERIC; }
+
+  virtual size_t get_header_kvrs_length() {
+    return Data::get_header_kvrs_length()
+        + 1 + 1   // subtype
+        + 1 + 1   // data length
+        + 1 + sizeof(value) + sizeof(value);  // limits
+  }
+
+  virtual void write_header_kvrs(TransmitPacketInterface& packet) {
+    Data::write_header_kvrs(packet);
+    packet.write_uint8(RECORDID_NUMERIC_SUBTYPE);
+    packet.write_uint8(get_subtype());
+    packet.write_uint8(RECORDID_NUMERIC_LENGTH);
+    packet.write_uint8(sizeof(value));
+    packet.write_uint8(RECORDID_NUMERIC_LIMITS);
+    serialize_data(min_val, packet);
+    serialize_data(max_val, packet);
+  }
+
+  uint8_t get_subtype();
+
+  virtual size_t get_payload_length() { return sizeof(value); }
+  virtual void write_payload(TransmitPacketInterface& packet) { serialize_data(value, packet); }
+  virtual void set_from_packet(ReceivePacketBuffer& packet) {
+    value = deserialize_data(packet);
+    telemetry_container.mark_data_updated(data_id); }
+  
+  void serialize_data(T data, TransmitPacketInterface& packet);
+  T deserialize_data(ReceivePacketBuffer& packet);
+
+protected:
+  Telemetry& telemetry_container;
+  size_t data_id;
+  T value;
+  T min_val, max_val;
+  bool frozen;
+};
+
+template <typename T, uint32_t array_count>
+class NumericArrayAccessor;
+
+// TODO: fix this partial specialization inheritance nightmare
+template <typename T, uint32_t array_count> 
+class NumericArrayBase : public Data {
+  friend class NumericArrayAccessor<T, array_count>;
+public:
+  NumericArrayBase(Telemetry& telemetry_container, 
+      const char* internal_name, const char* display_name,
+      const char* units, T elem_init_value):
+      Data(internal_name, display_name, units),
+      telemetry_container(telemetry_container),
+      min_val(elem_init_value), max_val(elem_init_value),
+      frozen(false) {
+    for (size_t i=0; i<array_count; i++) {
+      value[i] = elem_init_value;
+    }
+    data_id = telemetry_container.add_data(*this);
+  }
+
+  NumericArrayAccessor<T, array_count> operator[] (const int index) {
+    // TODO: add bounds checking here
+    // TODO: add "frozen" check
+    return NumericArrayAccessor<T, array_count>(*this, index);
+  }
+
+  NumericArrayBase<T, array_count>& set_limits(T min, T max) {
+    min_val = min;
+    max_val = max;
+    return *this;
+  }
+  
+  virtual uint8_t get_data_type() { return DATATYPE_NUMERIC_ARRAY; }
+
+  virtual size_t get_header_kvrs_length() {
+    return Data::get_header_kvrs_length()
+        + 1 + 1   // subtype
+        + 1 + 1   // data length
+        + 1 + 4   // array length
+        + 1 + sizeof(value[0]) + sizeof(value[0]);  // limits
+  }
+
+  virtual void write_header_kvrs(TransmitPacketInterface& packet) {
+    Data::write_header_kvrs(packet);
+    packet.write_uint8(RECORDID_NUMERIC_SUBTYPE);
+    packet.write_uint8(get_subtype());
+    packet.write_uint8(RECORDID_NUMERIC_LENGTH);
+    packet.write_uint8(sizeof(value[0]));
+    packet.write_uint8(RECORDID_ARRAY_COUNT);
+    packet.write_uint32(array_count);
+    packet.write_uint8(RECORDID_NUMERIC_LIMITS);
+    serialize_data(min_val, packet);
+    serialize_data(max_val, packet);
+  }
+
+  virtual uint8_t get_subtype() = 0;
+
+  virtual size_t get_payload_length() { return sizeof(value); }
+  virtual void write_payload(TransmitPacketInterface& packet) {
+    for (size_t i=0; i<array_count; i++) { serialize_data(this->value[i], packet); } }
+  virtual void set_from_packet(ReceivePacketBuffer& packet) {
+    for (size_t i=0; i<array_count; i++) { value[i] = deserialize_data(packet); }
+    telemetry_container.mark_data_updated(data_id); }
+
+  virtual void serialize_data(T data, TransmitPacketInterface& packet) = 0;
+  virtual T deserialize_data(ReceivePacketBuffer& packet) = 0;
+  
+protected:
+  Telemetry& telemetry_container;
+  size_t data_id;
+  T value[array_count];
+  T min_val, max_val;
+  bool frozen;
+};
+
+template <typename T, uint32_t array_count>
+class NumericArrayAccessor {
+public:
+  NumericArrayAccessor(NumericArrayBase<T, array_count>& container, size_t index) :
+    container(container), index(index) { }
+
+  T operator = (T b) {
+    if (!container.frozen) {
+      container.value[index] = b;
+      container.telemetry_container.mark_data_updated(container.data_id);
+    }
+    return container.value[index];
+  }
+
+  operator T() {
+    return container.value[index];
+  }
+
+protected:
+  NumericArrayBase<T, array_count>& container;
+  size_t index;
+};
+
+template <typename T, uint32_t array_count> 
+class NumericArray : public NumericArrayBase<T, array_count> {
+  NumericArray(Telemetry& telemetry_container, 
+      const char* internal_name, const char* display_name,
+      const char* units, T elem_init_value);
+  virtual uint8_t get_subtype();
+  virtual void write_payload(TransmitPacketInterface& packet);
+  virtual T deserialize_data(ReceivePacketBuffer& packet);
+};
+
+template <uint32_t array_count> 
+class NumericArray<uint8_t, array_count> : public NumericArrayBase<uint8_t, array_count> {
+public:
+  NumericArray(Telemetry& telemetry_container, 
+      const char* internal_name, const char* display_name,
+      const char* units, uint8_t elem_init_value):
+      NumericArrayBase<uint8_t, array_count>(
+          telemetry_container, internal_name, display_name,
+          units, elem_init_value) {};
+  virtual uint8_t get_subtype() {return NUMERIC_SUBTYPE_UINT; }
+  virtual void serialize_data(uint8_t data, TransmitPacketInterface& packet) {
+    packet.write_uint8(data); }
+  virtual uint8_t deserialize_data(ReceivePacketBuffer& packet) {
+    return packet.read_uint8(); }
+};
+
+template <uint32_t array_count> 
+class NumericArray<uint16_t, array_count> : public NumericArrayBase<uint16_t, array_count> {
+public:
+  NumericArray(Telemetry& telemetry_container, 
+      const char* internal_name, const char* display_name,
+      const char* units, uint16_t elem_init_value):
+      NumericArrayBase<uint16_t, array_count>(
+          telemetry_container, internal_name, display_name,
+          units, elem_init_value) {};
+  virtual uint8_t get_subtype() {return NUMERIC_SUBTYPE_UINT; }
+  virtual void serialize_data(uint16_t data, TransmitPacketInterface& packet) {
+    packet.write_uint16(data); }
+  virtual uint16_t deserialize_data(ReceivePacketBuffer& packet) {
+    return packet.read_uint16(); }
+};
+
+template <uint32_t array_count> 
+class NumericArray<uint32_t, array_count> : public NumericArrayBase<uint32_t, array_count> {
+public:
+  NumericArray(Telemetry& telemetry_container, 
+      const char* internal_name, const char* display_name,
+      const char* units, uint32_t elem_init_value):
+      NumericArrayBase<uint32_t, array_count>(
+          telemetry_container, internal_name, display_name,
+          units, elem_init_value) {};
+  virtual uint8_t get_subtype() {return NUMERIC_SUBTYPE_UINT; }
+  virtual void serialize_data(uint32_t data, TransmitPacketInterface& packet) {
+    packet.write_uint32(data); }
+  virtual uint32_t deserialize_data(ReceivePacketBuffer& packet) {
+    return packet.read_uint32(); }
+};
+
+template <uint32_t array_count> 
+class NumericArray<float, array_count> : public NumericArrayBase<float, array_count> {
+public:
+  NumericArray(Telemetry& telemetry_container, 
+      const char* internal_name, const char* display_name,
+      const char* units, float elem_init_value):
+      NumericArrayBase<float, array_count>(
+          telemetry_container, internal_name, display_name,
+          units, elem_init_value) {};
+  virtual uint8_t get_subtype() {return NUMERIC_SUBTYPE_FLOAT; }
+  virtual void serialize_data(float data, TransmitPacketInterface& packet) {
+    packet.write_float(data); }
+  virtual float deserialize_data(ReceivePacketBuffer& packet) {
+    return packet.read_float(); }
+};
+
+}
+
+#endif