#include <stdint.h>
#include <stddef.h>

struct Message {
	uint32_t id;
	uint32_t time;
	uint32_t position;
    int32_t force;
    uint8_t duty_cycle;
    uint8_t wave_form;
};

// 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;
};

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


// 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 )

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, uint32_t position, int32_t force )
{
	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->force = force;
	msg->position = position;
	msg->duty_cycle = 0
	msg->wave_form = 0
	// update write-pointer
	ddr_widx = widx = next_widx;
}


static inline char uart_recv_byte()
{
    for(;;) {
        uint8_t lsr = CT_UART.LSR;
        if( lsr & 0x1e )
            __halt();  // 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 )
            __halt();  // line does not fit in buffer
        msg[ len++ ] = c;
    }

    return len;
}

// receive and parse measurement message from load cell
int32_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] != '-'))
        __halt();

    // parse the remainder as integer
    int32_t value = 0;
    uint8_t i;
    for( i = 2; i < len; i++ ) {
        if( msg[i] < '0' || msg[i] > '9' )
            __halt();
        value = value * 10 + ( msg[i] - '0' );
    }
    if (msg[1] == '-')
            value *= -1;

    return value;
}


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

void main() {
	initialize();

	uint32_t id = 0;
	int32_t force = 0;
	uint32_t position =0;



	for(;;) {


		// parse and interpret message from load cell
        force = receive_measurement();

		// read position value from decoder
 		position = *position_var;

		send_message( ++id,force,position );
		__delay_cycles( 10000 );
	}
}