#include <stdint.h>
#include <stddef.h>
#include "pru_uart.h"
#include "pru_ecap.h"
#include "sys_gpio.h"

// define PWM inputs for motor controll
#define EPWM1A  ( *(uint16_t volatile *)0x48302212 )
#define EPWM1B  ( *(uint16_t volatile *)0x48302214 )

// encoder position in other PRU core's memory
#define position_var ((uint32_t const volatile *)0x00002000)

struct Message {
	uint32_t id;
	uint32_t timestamp;
	uint32_t position;
	int16_t force;
	int16_t control_signal;
	int16_t motor_effort;
};

// layout of shared ddr3 memory (filled in by loader)
struct DDRLayout {
	Message volatile *msgbuf;
	uint16_t num_msgs;
	uint16_t msg_size;
};

struct SharedVars {
	// set by pru before halting
	char const *abort_file;
	int abort_line;
	// read-pointer updated by python
	uint16_t ridx;
	uint16_t signal[1000];
};

far struct DDRLayout ddr __attribute__((location(0x10000))) = {};
far struct SharedVars volatile shmem __attribute__((location(0x10100))) = {};

static inline uint32_t timestamp_cycles()
{
    return CT_ECAP.TSCTR;
}

// for easier debugging, record where in the source code we halted
__attribute__((noreturn))
void abort_at( char const *file, int line )
{
	shmem.abort_file = file;
	shmem.abort_line = line;
	for(;;) __halt();
}

static inline void assert_at( bool cond, char const *file, int line )
{
	if( ! cond )
		abort_at( file, line );
}

#define abort() abort_at( __FILE__, __LINE__ )
#define assert(cond) assert_at( (cond), __FILE__, __LINE__ )

// local copy of write-pointer
static uint16_t widx = 0;

// global var for write-pointer is located right after message ringbuffer
#define ddr_msgbuf_end	( ddr.msgbuf + ddr.num_msgs )
#define ddr_widx	( *(uint16_t volatile *)ddr_msgbuf_end )

// receive byte from uart
static inline char uart_recv_byte()
{
    for(;;) {
        uint8_t lsr = CT_UART.LSR;
        if( lsr & 0x1e )
            abort();  // receive-error occurred
        if( lsr & 0x01 )
            return (char) CT_UART.RBR;
    }
}


// receive CR-terminated line from uart
static inline uint8_t uart_recv_line( char volatile msg[], uint8_t maxlen )
{
    uint8_t len = 0;

    for(;;) {
        char c = uart_recv_byte();
        if( c == '\r' )
            break;  // found end of line
        if( len == maxlen )
            abort();  // line does not fit in buffer
        msg[ len++ ] = c;
    }

    return len;
}

int16_t receive_measurement()
{
    // allocate buffer at fixed address for debugging convenience
    static char volatile msg[8] __attribute__((location(0x1f00)));

    // receive line from uart
    uint8_t len = uart_recv_line( msg, sizeof msg );

    // verify length and prefix
    if( len != 8 || msg[0] != 'N' || (msg[1] != '+' && msg[1] != '-'))
        abort();

    // parse the remainder as integer
    int16_t value = 0;
    uint8_t i;
    for( i = 2; i < len; i++ ) {
        if( msg[i] < '0' || msg[i] > '9' )
            abort();
        value = value * 10 + ( msg[i] - '0' );
    }
    if (msg[1] == '-')
            value *= -1;

    return value;
}


void initialize()
{
	// perform sanity-checking
	assert( 0x80000000 <= (uint32_t)ddr.msgbuf );
	assert( ddr.msgbuf < ddr_msgbuf_end );
	assert( ddr.msg_size == sizeof(Message) );

	assert( ddr_widx == widx );
	assert( shmem.ridx == widx );
}


static inline uint16_t next_idx( uint16_t idx )
{
	if( ++idx == ddr.num_msgs )
		idx = 0;
	return idx;
}


void send_message( uint32_t id, int16_t current_force,uint32_t current_position, int16_t input, int16_t output)
{
	uint16_t next_widx = next_idx( widx );

	if( next_widx == shmem.ridx ) {
		// can't send message, ringbuffer is full
		abort();
	}

	Message volatile *msg = &ddr.msgbuf[ widx ];

	// fill in contents of message
	msg->id = id;
	msg->position = current_position;
	msg->force = current_force;
	msg->timestamp = timestamp_cycles();
	msg->control_signal = input;
	msg->motor_effort = output;
	// update write-pointer
	ddr_widx = widx = next_widx;
}

void main() {
    int16_t control_signal = 0;
	int32_t error[3];
    CT_UART.THR = 'S';
    CT_UART.THR = 'N';
    CT_UART.THR = '\r';
    initialize();

	uint32_t id =0;
    uint32_t reference_count = *position_var; // initil reading from decoder as unit32

	uint8_t counter = 0;
    gpio_set_one_low(&GPIO0,31);

    while (true) {
	    int16_t force = receive_measurement();
        uint32_t position = *position_var;

		// PID parameters
		int16_t Kp = 100;
        int16_t Ki = 0;
        int16_t Kd = 0;
        int16_t A[3] = {0};
		A[0] = Kp + Ki + Kd;
		A[1] = -Kp -2*Kd;
		A[2] = Kd;
	    int16_t input_signal = shmem.signal[counter];

		// Control logic work in progress
		error[2] = error[1];
        error[1] = error[0];
        error[0] = input_signal + reference_count; // current reading from decoder
        error[0] = error[0] - position;
		control_signal = control_signal + A[0] * error[0] + A[1] * error[1] + A[2] * error[2];

		// check if motor direction must change
		if (control_signal < 0) {
            gpio_set_one_low(&GPIO0,31);
		} else {
			gpio_set_one_high(&GPIO0,31);
		}

		// place upper bound on control signal
		if (control_signal > 4000)
			control_signal = 4000;
    	// place lower bound on control signal
        if (control_signal < 600)
			control_signal = 600;
		// check for fault condition
		if (position > 5000 && position < 4294967000)
	    	EPWM1A = 0;
		else
	    	EPWM1A = control_signal;
		//report to python
		send_message( ++id,force, position, input_signal,control_signal);
		++counter;
		// reset counter to enforce periodicy
		if (counter > 999)
			counter = 0;
    }
}