#include <stdint.h>

struct StepperInterface {
    uint32_t target_pos;
    uint32_t current_pos;
    bool halt_requested;
};
StepperInterface shmem __attribute__((cregister("LOCAL", near))) = {};
//StepperInterface shmem __attribute__((location(0))) = {};


// define some r30 bits
#define CW  (1u << 0)
#define CCW (1u << 1)

uint32_t volatile register __R30;

#define delay_us(n) __delay_cycles((n) * 200u)
#define delay_ms(n) delay_us((n) * 1000u)

static inline void enable()
{
    // this could either control the ENA signal or perhaps disable the
    // control signals.  either way, probably want to use normal GPIO for
    // it since the PRU direct gpio (via R30) have random values at boot.
}

static inline void disable()
{
}

static inline void deassert_CW_CCW() {  __R30 = 0;  }
static inline void assert_CW() {  __R30 = CW;  }
static inline void assert_CCW() {  __R30 = CCW;  }

// CW/CCW version
int main()
{
    uint32_t pos = shmem.current_pos;
    deassert_CW_CCW();
    delay_us(1);  // just to be paranoid
    enable();
    delay_ms(200);
    while( ! shmem.halt_requested ) {
        int32_t delta = shmem.target_pos - pos;
        if( delta == 0 )
            continue;
        // XXX optional: check for excessive delta
        if( delta < 0 ) {
            --pos;
            assert_CCW();
        } else {
            ++pos;
            assert_CW();
        }
        shmem.current_pos = pos;  // for diagnostic purposes
        delay_us(1);
        deassert_CW_CCW();
        delay_us(1);
    }
    disable();
    __halt();
}