/*! ----------------------------------------------------------------------------
 *  @file    main.c
 *  @brief   Single-sided two-way ranging (SS TWR) responder example code
 *
 *           This is a simple code example which acts as the responder in a SS TWR distance measurement exchange. This application waits for a "poll"
 *           message (recording the RX time-stamp of the poll) expected from the "SS TWR initiator" example code (companion to this application), and
 *           then sends a "response" message to complete the exchange. The response message contains all the time-stamps recorded by this application,
 *           including the calculated/predicted TX time-stamp for the response message itself. The companion "SS TWR initiator" 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
 */
#include <string.h>

#include "deca_device_api.h"
#include "deca_regs.h"
#include "lcd.h"
#include "port.h"

/* Example application name and version to display on LCD screen. */
#define APP_NAME "SS TWR RESP v1.2"

/* Default communication configuration. We use here EVK1000's mode 4. See NOTE 1 below. */
static dwt_config_t config = {
    2,               /* Channel number. */
    DWT_PRF_64M,     /* Pulse repetition frequency. */
    DWT_PLEN_128,    /* Preamble length. Used in TX only. */
    DWT_PAC8,        /* Preamble acquisition chunk size. Used in RX only. */
    9,               /* TX preamble code. Used in TX only. */
    9,               /* RX preamble code. Used in RX only. */
    0,               /* 0 to use standard SFD, 1 to use non-standard SFD. */
    DWT_BR_6M8,      /* Data rate. */
    DWT_PHRMODE_STD, /* PHY header mode. */
    (129 + 8 - 8)    /* SFD timeout (preamble length + 1 + SFD length - PAC size). Used in RX only. */
};

/* Default antenna delay values for 64 MHz PRF. See NOTE 2 below. */
#define TX_ANT_DLY 16436
#define RX_ANT_DLY 16436

/* Frames used in the ranging process. See NOTE 3 below. */
static uint8 rx_poll_msg[] = {0x41, 0x88, 0, 0xCA, 0xDE, 'W', 'A', 'V', 'E', 0xE0, 0, 0};
static uint8 tx_resp_msg[] = {0x41, 0x88, 0, 0xCA, 0xDE, 'V', 'E', 'W', 'A', 0xE1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
/* Length of the common part of the message (up to and including the function code, see NOTE 3 below). */
#define ALL_MSG_COMMON_LEN 10
/* Index to access some of the fields in the frames involved in the process. */
#define ALL_MSG_SN_IDX 2
#define RESP_MSG_POLL_RX_TS_IDX 10
#define RESP_MSG_RESP_TX_TS_IDX 14
#define RESP_MSG_TS_LEN 4
/* Frame sequence number, incremented after each transmission. */
static uint8 frame_seq_nb = 0;

/* Buffer to store received messages.
 * Its size is adjusted to longest frame that this example code is supposed to handle. */
#define RX_BUF_LEN 12
static uint8 rx_buffer[RX_BUF_LEN];

/* Hold copy of status register state here for reference so that it can be examined at a debug breakpoint. */
static uint32 status_reg = 0;

/* UWB microsecond (uus) to device time unit (dtu, around 15.65 ps) conversion factor.
 * 1 uus = 512 / 499.2 µs and 1 µs = 499.2 * 128 dtu. */
#define UUS_TO_DWT_TIME 65536

/* Delay between frames, in UWB microseconds. See NOTE 1 below. */
#define POLL_RX_TO_RESP_TX_DLY_UUS 330

/* Timestamps of frames transmission/reception.
 * As they are 40-bit wide, we need to define a 64-bit int type to handle them. */
typedef unsigned long long uint64;
static uint64 poll_rx_ts;
static uint64 resp_tx_ts;

/* Declaration of static functions. */
static uint64 get_rx_timestamp_u64(void);
static void resp_msg_set_ts(uint8 *ts_field, const uint64 ts);

/*! ------------------------------------------------------------------------------------------------------------------
 * @fn main()
 *
 * @brief Application entry point.
 *
 * @param  none
 *
 * @return none
 */
int responderexample(void)
{
    /* Start with board specific hardware init. */
    peripherals_init();

    /* Display application name on LCD. */
    lcd_display_str(APP_NAME);

    /* 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. */
    reset_DW1000(); /* Target specific drive of RSTn line into DW1000 low for a period. */
    spi_set_rate_low();
    if (dwt_initialise(DWT_LOADUCODE) == DWT_ERROR)
    {
        lcd_display_str("INIT FAILED");
        while (1)
        { };
    }
    spi_set_rate_high();

    /* Configure DW1000. See NOTE 5 below. */
    dwt_configure(&config);

    /* Apply default antenna delay value. See NOTE 2 below. */
    dwt_setrxantennadelay(RX_ANT_DLY);
    dwt_settxantennadelay(TX_ANT_DLY);

    /* Loop forever responding to ranging requests. */
    while (1)
    {
        /* Activate reception immediately. */
        dwt_rxenable(DWT_START_RX_IMMEDIATE);

        /* Poll for reception of a frame or error/timeout. See NOTE 6 below. */
        while (!((status_reg = dwt_read32bitreg(SYS_STATUS_ID)) & (SYS_STATUS_RXFCG | SYS_STATUS_ALL_RX_ERR)))
        { };

        if (status_reg & SYS_STATUS_RXFCG)
        {
            uint32 frame_len;

            /* Clear good RX frame event in the DW1000 status register. */
            dwt_write32bitreg(SYS_STATUS_ID, SYS_STATUS_RXFCG);

            /* A frame has been received, read it into the local buffer. */
            frame_len = dwt_read32bitreg(RX_FINFO_ID) & RX_FINFO_RXFL_MASK_1023;
            if (frame_len <= RX_BUFFER_LEN)
            {
                dwt_readrxdata(rx_buffer, frame_len, 0);
            }

            /* Check that the frame is a poll sent by "SS TWR initiator" 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_poll_msg, ALL_MSG_COMMON_LEN) == 0)
            {
                uint32 resp_tx_time;
                int ret;

                /* Retrieve poll reception timestamp. */
                poll_rx_ts = get_rx_timestamp_u64();

                /* Compute final message transmission time. See NOTE 7 below. */
                resp_tx_time = (poll_rx_ts + (POLL_RX_TO_RESP_TX_DLY_UUS * UUS_TO_DWT_TIME)) >> 8;
                dwt_setdelayedtrxtime(resp_tx_time);

                /* Response TX timestamp is the transmission time we programmed plus the antenna delay. */
                resp_tx_ts = (((uint64)(resp_tx_time & 0xFFFFFFFEUL)) << 8) + TX_ANT_DLY;

                /* Write all timestamps in the final message. See NOTE 8 below. */
                resp_msg_set_ts(&tx_resp_msg[RESP_MSG_POLL_RX_TS_IDX], poll_rx_ts);
                resp_msg_set_ts(&tx_resp_msg[RESP_MSG_RESP_TX_TS_IDX], resp_tx_ts);

                /* Write and send the response message. See NOTE 9 below. */
                tx_resp_msg[ALL_MSG_SN_IDX] = frame_seq_nb;
                dwt_writetxdata(sizeof(tx_resp_msg), tx_resp_msg, 0); /* Zero offset in TX buffer. */
                dwt_writetxfctrl(sizeof(tx_resp_msg), 0, 1); /* Zero offset in TX buffer, ranging. */
                ret = dwt_starttx(DWT_START_TX_DELAYED);

                /* If dwt_starttx() returns an error, abandon this ranging exchange and proceed to the next one. See NOTE 10 below. */
                if (ret == DWT_SUCCESS)
                {
                    /* Poll DW1000 until TX frame sent event set. See NOTE 6 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 poll message (modulo 256). */
                    frame_seq_nb++;
                }
            }
        }
        else
        {
            /* Clear RX error events in the DW1000 status register. */
            dwt_write32bitreg(SYS_STATUS_ID, SYS_STATUS_ALL_RX_ERR);

            /* Reset RX to properly reinitialise LDE operation. */
            dwt_rxreset();
        }
    }
}

/*! ------------------------------------------------------------------------------------------------------------------
 * @fn get_rx_timestamp_u64()
 *
 * @brief Get the RX time-stamp in a 64-bit variable.
 *        /!\ This function assumes that length of time-stamps is 40 bits, for both TX and RX!
 *
 * @param  none
 *
 * @return  64-bit value of the read time-stamp.
 */
static uint64 get_rx_timestamp_u64(void)
{
    uint8 ts_tab[5];
    uint64 ts = 0;
    int i;
    dwt_readrxtimestamp(ts_tab);
    for (i = 4; i >= 0; i--)
    {
        ts <<= 8;
        ts |= ts_tab[i];
    }
    return ts;
}

/*! ------------------------------------------------------------------------------------------------------------------
 * @fn final_msg_set_ts()
 *
 * @brief Fill a given timestamp field in the response message with the given value. In the timestamp fields of the
 *        response message, the least significant byte is at the lower address.
 *
 * @param  ts_field  pointer on the first byte of the timestamp field to fill
 *         ts  timestamp value
 *
 * @return none
 */
static void resp_msg_set_ts(uint8 *ts_field, const uint64 ts)
{
    int i;
    for (i = 0; i < RESP_MSG_TS_LEN; i++)
    {
        ts_field[i] = (ts >> (i * 8)) & 0xFF;
    }
}

/*****************************************************************************************************************************************************
 * NOTES:
 *
 * 1. The single-sided two-way ranging scheme implemented here has to be considered carefully as the accuracy of the distance measured is highly
 *    sensitive to the clock offset error between the devices and the length of the response delay between frames. To achieve the best possible
 *    accuracy, this response delay must be kept as low as possible. In order to do so, 6.8 Mbps data rate is used in this example and the response
 *    delay between frames is defined as low as possible. The user is referred to User Manual for more details about the single-sided two-way ranging
 *    process.
 * 2. 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.
 * 3. The frames used here are Decawave specific ranging frames, complying with the IEEE 802.15.4 standard data frame encoding. The frames are the
 *    following:
 *     - a poll message sent by the initiator to trigger the ranging exchange.
 *     - a response message sent by the responder to complete the exchange and provide all information needed by the initiator 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 4 below.
 *     - byte 7/8: source address, see NOTE 4 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 -> 13: poll message reception timestamp.
 *     - byte 14 -> 17: response message transmission timestamp.
 *    All messages end with a 2-byte checksum automatically set by DW1000.
 * 4. 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.
 * 5. 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.
 * 6. 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.
 * 7. 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.
 * 8. 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.
 * 9. 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()).
 * 10. When running this example on the EVB1000 platform with the POLL_RX_TO_RESP_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 and simply goes back to awaiting another poll message. If this error handling code was not here, a late dwt_starttx() would
 *     result in the code flow getting stuck waiting subsequent RX event that will will never come. The companion "initiator" example (ex_06a) should
 *     timeout from awaiting the "response" and proceed to send another poll in due course to initiate another ranging exchange.
 * 11. 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.
 ****************************************************************************************************************************************************/

