text: /*! ----------------------------------------------------------------------------
   *  @file    main.c
   *  @brief   Double-sided two-way ranging (DS TWR) initiator example code
   *
   *           This is a simple code example which acts as the initiator in a DS TWR distance measurement exchange. This application sends a "poll"
   *           frame (recording the TX time-stamp of the poll), and then waits for a "response" message expected from the "DS TWR responder" example
   *           code (companion to this application). When the response is received its RX time-stamp is recorded and we send a "final" message to
   *           complete the exchange. The final message contains all the time-stamps recorded by this application, including the calculated/predicted TX
   *           time-stamp for the final message itself. The companion "DS TWR responder" example application works out the time-of-flight over-the-air
   *           and, thus, the estimated distance between the two devices.
   *
   * @attention
   *
   * Copyright 2015 (c) Decawave Ltd, Dublin, Ireland.
   *
   * All rights reserved.
   *
   * @author Decawave
   */
  
  /*
   * initiator.c
   *
   *  Created on: Feb 23, 2021
   *      Author: kostasdeligiorgis
   */
  
  #include <DWM_functions.h>
  #include "main.h"
  #include "deca_device_api.h"
  #include "deca_regs.h"
  
  #include "deca_timestamps.h"
  
  #include "port.h"
  
  #include "usbd_cdc_if.h"
  
  //#define RNG_DELAY_MS 1000  // Original
  //#define RNG_DELAY_MS 100
  #define RNG_DELAY_MS 650
  
  /* Default communication configuration. We use here EVK1000's default mode (mode 3). */
  static dwt_config_t config = {
      2,               /* Channel number. */
      DWT_PRF_64M,     /* Pulse repetition frequency. */
      DWT_PLEN_1024,   /* Preamble length. Used in TX only. */
      DWT_PAC32,       /* Preamble acquisition chunk size. Used in RX only. */
      9,               /* TX preamble code. Used in TX only. */
      9,               /* RX preamble code. Used in RX only. */
      1,               /* 0 to use standard SFD, 1 to use non-standard SFD. */
      DWT_BR_110K,     /* Data rate. */
      DWT_PHRMODE_STD, /* PHY header mode. */
      (1025 + 64 - 32) /* SFD timeout (preamble length + 1 + SFD length - PAC size). Used in RX only. */
  };
  
  /* Default antenna delay values for 64 MHz PRF. See NOTE 1 below. */
  #define TX_ANT_DLY     16505
  #define RX_ANT_DLY     16505
  
  /* Length of the common part of the message (up to and including the function code, see NOTE 2 below). */
  #define ALL_MSG_COMMON_LEN            10
  
  /* Indexes to access some of the fields in the frames defined above. */
  #define ALL_MSG_SN_IDX                2
  #define FINAL_MSG_TS_LEN              4
  #define FINAL_MSG_POLL_TX_TS_IDX      10
  #define FINAL_MSG_RESP_RX_TS_IDX      14
  #define FINAL_MSG_FINAL_TX_TS_IDX     18
  
  /* Frame sequence number, incremented after each transmission. */
  static uint8_t frame_seq_nb = 0;
  
  /* UWB microsecond (uus) to device time unit (dtu, around 15.65 ps) conversion factor.
   * 1 uus = 512 / 499.2 ms and 1 ms = 499.2 * 128 dtu. */
  #define UUS_TO_DWT_TIME   65536
  
  /* Speed of light in air, in metres per second. */
  #define SPEED_OF_LIGHT  299702547
  
  
  /* Delay between frames, in UWB microseconds. See NOTE 4 below. */
  /* This is the delay from the end of the frame transmission to the enable of the receiver, as programmed for the DW1000's wait for response feature. */
  #define POLL_TX_TO_RESP_RX_DLY_UUS  300  //  Original
  //#define POLL_TX_TO_RESP_RX_DLY_UUS 150 // it works
  
  /* This is the delay from Frame RX timestamp to TX reply timestamp used for calculating/setting the DW1000's delayed TX function. This includes the
   * frame length of approximately 2.66 ms with above configuration. */
  //#define RESP_RX_TO_FINAL_TX_DLY_UUS 3100  // Original
  #define RESP_RX_TO_FINAL_TX_DLY_UUS 3500
  
  /* Receive response timeout. See NOTE 5 below. */
  //#define RESP_RX_TIMEOUT_UUS 2700  // Original
  #define RESP_RX_TIMEOUT_UUS 3500
  
  /* Preamble timeout, in multiple of PAC size. See NOTE 6 below. */
  //#define PRE_TIMEOUT 8
  #define PRE_TIMEOUT 30  
  
  /* Frames used in the ranging process. See NOTE 2 below. */
  static uint8_t tx_poll_msg[]  = {0x41, 0x88, 0, 0xCA, 0xDE, 'W', 'A', 'V', 'E', 0x21, 0, 0};  // 0x21 = Ranging Tag initial Poll Response
  static uint8_t rx_resp_msg[]  = {0x41, 0x88, 0, 0xCA, 0xDE, 'V', 'E', 'W', 'A', 0x10, 0x02, 0, 0, 0, 0}; // 0x10 = Activity control from infrastructure  // 0x02 = something its not finish
  static uint8_t tx_final_msg[] = {0x41, 0x88, 0, 0xCA, 0xDE, 'W', 'A', 'V', 'E', 0x23, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};  // 0x32 = Ranging Tag Final response message with embedded Tx time
  
  /* Buffer to store received response message.
   * Its size is adjusted to longest frame that this example code is supposed to handle. */
  #define RX_BUF_LEN  20
  static uint8_t rx_buffer[RX_BUF_LEN];
  
  /* Time-stamps of frames transmission/reception, expressed in device time units.
  * As they are 40-bit wide, we need to define a 64-bit int type to handle them. */
  uint32_t frameLen, final_tx_time;
  uint64_t poll_tx_ts, resp_rx_ts, final_tx_ts;
  
  /* Hold copy of status register state here for reference so that it can be examined at a debug breakpoint. */
  static uint32_t status = 0;
  
  /*! ------------------------------------------------------------------------------------------------------------------
   * @fn main()
   *
   * @brief Application entry point.
   *
   * @param  none
   *
   * @return none
   */
  void ds_twr_init(void)
  {
  
  	/* Reset and initialise DW1000.
  	 * For initialisation, DW1000 clocks must be temporarily set to crystal speed. After initialisation SPI rate can be increased for optimum
  	 * performance. */
  	deca_reset(); /* Target specific drive of RSTn line into DW1000 low for a period. */
  
  	port_set_dw1000_slowrate();
  
  	if (dwt_initialise(DWT_LOADUCODE) == DWT_ERROR)
  	{
  		while (1){};
  	}
  
  	port_set_dw1000_fastrate();
  
      /* Configure DW1000. See NOTE 7 below. */
  	dwt_configure(&config);
  
      /* Apply default antenna delay value. See NOTE 1 below. */
  	dwt_settxantennadelay(TX_ANT_DLY);
  	dwt_setrxantennadelay(RX_ANT_DLY);
  
  
      /* Set expected response's delay and timeout. See NOTE 4, 5 and 6 below.
       * As this example only handles one incoming frame with always the same delay and timeout, those values can be set here once for all. */
  	dwt_setrxaftertxdelay(POLL_TX_TO_RESP_RX_DLY_UUS);
  	dwt_setrxtimeout(RESP_RX_TIMEOUT_UUS);
      dwt_setpreambledetecttimeout(PRE_TIMEOUT);
  
      /* Loop forever initiating ranging exchanges. */
  	while(1)
  	{
          /* Write frame data to DW1000 and prepare transmission. See NOTE 8 below. */
  		tx_poll_msg[ALL_MSG_COMMON_LEN] = frame_seq_nb;
  		dwt_writetxdata(sizeof(tx_poll_msg), tx_poll_msg, 0);  /* Zero offset in TX buffer. */
  		dwt_writetxfctrl(sizeof(tx_poll_msg), 0, 1);           /* Zero offset in TX buffer, ranging. */
  
          /* Start transmission, indicating that a response is expected so that reception is enabled automatically after the frame is sent and the delay
           * set by dwt_setrxaftertxdelay() has elapsed. */
  		dwt_starttx(DWT_START_TX_IMMEDIATE | DWT_RESPONSE_EXPECTED);
  
  		/* We assume that the transmission is achieved correctly, poll for reception of a frame or error/timeout. See NOTE 9 below. */
  		do {
  	    	status = dwt_read32bitreg(SYS_STATUS_ID);
  		} while (!(status & (SYS_STATUS_RXFCG | SYS_STATUS_ALL_RX_TO | SYS_STATUS_ALL_RX_ERR)));
  
          /* Increment frame sequence number after transmission of the poll message (modulo 256). */
  		frame_seq_nb ++;
  
  		if(status & SYS_STATUS_RXFCG)
  		{
  
              /* Clear good RX frame event and TX frame sent in the DW1000 status register. */
  			dwt_write32bitreg(SYS_STATUS_ID, SYS_STATUS_RXFCG | SYS_STATUS_TXFRS);
  
  			memset(rx_buffer, 0, RX_BUF_LEN);
  			// A frame has been received, copy it to our local buffer.
  			frameLen = dwt_read32bitreg(RX_FINFO_ID) & 0x0000007FUL;  // RX_FINFO_RXFLEN_MASK = 0x0000007FUL
  			if ( frameLen <= RX_BUF_LEN)
  			{
  				dwt_readrxdata(rx_buffer, frameLen, 0);
  			}
  
              /* Check that the frame is the expected response from the companion "DS TWR responder" example.
               * As the sequence number field of the frame is not relevant, it is cleared to simplify the validation of the frame. */
  			rx_buffer[ALL_MSG_SN_IDX] = 0;
  			if (memcmp(rx_buffer, rx_resp_msg, ALL_MSG_COMMON_LEN) == 0)
  			{
  				int ret;
  
  				poll_tx_ts = get_tx_timestamp_u64();
  				resp_rx_ts = get_rx_timestamp_u64();
  
                  /* Compute final message transmission time. See NOTE 10 below. */
  				final_tx_time = (resp_rx_ts + (RESP_RX_TO_FINAL_TX_DLY_UUS * UUS_TO_DWT_TIME)) >> 8;
  
  				dwt_setdelayedtrxtime(final_tx_time);
  
  				/* Final TX timestamp is the transmission time we programmed plus the TX antenna delay. */
  				final_tx_ts = (((uint64_t)(final_tx_time & 0xFFFFFFFEUL)) << 8) + TX_ANT_DLY;
  
                  /* Write all timestamps in the final message. See NOTE 11 below. */
  				final_msg_set_ts(&tx_final_msg[FINAL_MSG_POLL_TX_TS_IDX], poll_tx_ts);
  				final_msg_set_ts(&tx_final_msg[FINAL_MSG_RESP_RX_TS_IDX], resp_rx_ts);
  				final_msg_set_ts(&tx_final_msg[FINAL_MSG_FINAL_TX_TS_IDX], final_tx_ts);
  
                  /* Write and send final message. See NOTE 8 below. */
  				tx_final_msg[ALL_MSG_SN_IDX] = frame_seq_nb;
  				dwt_writetxdata(sizeof(tx_final_msg), tx_final_msg, 0);  /* Zero offset in TX buffer. */
  				dwt_writetxfctrl(sizeof(tx_final_msg), 0, 1); /* Zero offset in TX buffer, ranging. */
  
  				/* If dwt_starttx() returns an error, abandon this ranging exchange and proceed to the next one. See NOTE 12 below. */
  				ret = dwt_starttx(DWT_START_TX_DELAYED);
  				if (ret == DWT_SUCCESS){
  
                      /* Poll DW1000 until TX frame sent event set. See NOTE 9 below. */
  					while (!(dwt_read32bitreg(SYS_STATUS_ID) & SYS_STATUS_TXFRS)) {};
  
                      /* Clear TXFRS event. */
  					dwt_write32bitreg(SYS_STATUS_ID, SYS_STATUS_TXFRS);
  
  					/* Increment frame sequence number after transmission of the final message (modulo 256). */
  					frame_seq_nb ++;
  
  				}
  			}
  		}
  		else
  		{
              /* Clear RX error/timeout events in the DW1000 status register. */
  			dwt_write32bitreg(SYS_STATUS_ID, SYS_STATUS_ALL_RX_TO | SYS_STATUS_ALL_RX_ERR);
  
  			/* Reset RX to properly re-initialise LDE operation. */
  			dwt_rxreset();
  		}
  
          /* Execute a delay between ranging exchanges. */
  		Sleep(RNG_DELAY_MS);
  
  	}
  }
  
  /*****************************************************************************************************************************************************
   * NOTES:
   *
   * 1. The sum of the values is the TX to RX antenna delay, experimentally determined by a calibration process. Here we use a hard coded typical value
   *    but, in a real application, each device should have its own antenna delay properly calibrated to get the best possible precision when performing
   *    range measurements.
   * 2. The messages here are similar to those used in the DecaRanging ARM application (shipped with EVK1000 kit). They comply with the IEEE
   *    802.15.4 standard MAC data frame encoding and they are following the ISO/IEC:24730-62:2013 standard. The messages used are:
   *     - a poll message sent by the initiator to trigger the ranging exchange.
   *     - a response message sent by the responder allowing the initiator to go on with the process
   *     - a final message sent by the initiator to complete the exchange and provide all information needed by the responder to compute the
   *       time-of-flight (distance) estimate.
   *    The first 10 bytes of those frame are common and are composed of the following fields:
   *     - byte 0/1: frame control (0x8841 to indicate a data frame using 16-bit addressing).
   *     - byte 2: sequence number, incremented for each new frame.
   *     - byte 3/4: PAN ID (0xDECA).
   *     - byte 5/6: destination address, see NOTE 3 below.
   *     - byte 7/8: source address, see NOTE 3 below.
   *     - byte 9: function code (specific values to indicate which message it is in the ranging process).
   *    The remaining bytes are specific to each message as follows:
   *    Poll message:
   *     - no more data
   *    Response message:
   *     - byte 10: activity code (0x02 to tell the initiator to go on with the ranging exchange).
   *     - byte 11/12: activity parameter, not used here for activity code 0x02.
   *    Final message:
   *     - byte 10 -> 13: poll message transmission timestamp.
   *     - byte 14 -> 17: response message reception timestamp.
   *     - byte 18 -> 21: final message transmission timestamp.
   *    All messages end with a 2-byte checksum automatically set by DW1000.
   * 3. Source and destination addresses are hard coded constants in this example to keep it simple but for a real product every device should have a
   *    unique ID. Here, 16-bit addressing is used to keep the messages as short as possible but, in an actual application, this should be done only
   *    after an exchange of specific messages used to define those short addresses for each device participating to the ranging exchange.
   * 4. Delays between frames have been chosen here to ensure proper synchronisation of transmission and reception of the frames between the initiator
   *    and the responder and to ensure a correct accuracy of the computed distance. The user is referred to DecaRanging ARM Source Code Guide for more
   *    details about the timings involved in the ranging process.
   * 5. This timeout is for complete reception of a frame, i.e. timeout duration must take into account the length of the expected frame. Here the value
   *    is arbitrary but chosen large enough to make sure that there is enough time to receive the complete response frame sent by the responder at the
   *    110k data rate used (around 3 ms).
   * 6. The preamble timeout allows the receiver to stop listening in situations where preamble is not starting (which might be because the responder is
   *    out of range or did not receive the message to respond to). This saves the power waste of listening for a message that is not coming. We
   *    recommend a minimum preamble timeout of 5 PACs for short range applications and a larger value (e.g. in the range of 50% to 80% of the preamble
   *    length) for more challenging longer range, NLOS or noisy environments.
   * 7. In a real application, for optimum performance within regulatory limits, it may be necessary to set TX pulse bandwidth and TX power, (using
   *    the dwt_configuretxrf API call) to per device calibrated values saved in the target system or the DW1000 OTP memory.
   * 8. dwt_writetxdata() takes the full size of the message as a parameter but only copies (size - 2) bytes as the check-sum at the end of the frame is
   *    automatically appended by the DW1000. This means that our variable could be two bytes shorter without losing any data (but the sizeof would not
   *    work anymore then as we would still have to indicate the full length of the frame to dwt_writetxdata()).
   * 9. We use polled mode of operation here to keep the example as simple as possible but all status events can be used to generate interrupts. Please
   *    refer to DW1000 User Manual for more details on "interrupts". It is also to be noted that STATUS register is 5 bytes long but, as the event we
   *    use are all in the first bytes of the register, we can use the simple dwt_read32bitreg() API call to access it instead of reading the whole 5
   *    bytes.
   * 10. As we want to send final TX timestamp in the final message, we have to compute it in advance instead of relying on the reading of DW1000
   *     register. Timestamps and delayed transmission time are both expressed in device time units so we just have to add the desired response delay to
   *     response RX timestamp to get final transmission time. The delayed transmission time resolution is 512 device time units which means that the
   *     lower 9 bits of the obtained value must be zeroed. This also allows to encode the 40-bit value in a 32-bit words by shifting the all-zero lower
   *     8 bits.
   * 11. In this operation, the high order byte of each 40-bit timestamps is discarded. This is acceptable as those time-stamps are not separated by
   *     more than 2**32 device time units (which is around 67 ms) which means that the calculation of the round-trip delays (needed in the
   *     time-of-flight computation) can be handled by a 32-bit subtraction.
   * 12. When running this example on the EVB1000 platform with the RESP_RX_TO_FINAL_TX_DLY response delay provided, the dwt_starttx() is always
   *     successful. However, in cases where the delay is too short (or something else interrupts the code flow), then the dwt_starttx() might be issued
   *     too late for the configured start time. The code below provides an example of how to handle this condition: In this case it abandons the
   *     ranging exchange to try another one after 1 second. If this error handling code was not here, a late dwt_starttx() would result in the code
   *     flow getting stuck waiting for a TX frame sent event that will never come. The companion "responder" example (ex_05b) should timeout from
   *     awaiting the "final" and proceed to have its receiver on ready to poll of the following exchange.
   * 13. The user is referred to DecaRanging ARM application (distributed with EVK1000 product) for additional practical example of usage, and to the
   *     DW1000 API Guide for more details on the DW1000 driver functions.
   ****************************************************************************************************************************************************/
  