Subversion Repositories neo430

// #################################################################################################

// #  < neo430_freq_gen.c - Frequency Generator helper functions >                                 #

// # ********************************************************************************************* #

// # BSD 3-Clause License                                                                          #

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// # Copyright (c) 2020, Stephan Nolting. All rights reserved.                                     #

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// # The NEO430 Processor - https://github.com/stnolting/neo430                                    #

// #################################################################################################

#include "neo430.h"

#include "neo430_freq_gen.h"

// Private function prototypes

static uint32_t neo430_freq_gen_nco_real_output(uint16_t tuning_word, uint16_t prsc_shift);

/* ------------------------------------------------------------

 * INFO Enable programmable frequency output channel ch (0..2)

 * ------------------------------------------------------------ */

void neo430_freq_gen_enable_ch(uint16_t ch) {

  if (ch > 2) {

    return;

  }

  FREQ_GEN_CT |= (1 << (FREQ_GEN_CT_CH0_EN+ch));

}

/* ------------------------------------------------------------

 * INFO Disable programmable frequency output channel ch (0..2)

 * ------------------------------------------------------------ */

void neo430_freq_gen_disable_ch(uint16_t ch) {

  if (ch > 2) {

    return;

  }

  FREQ_GEN_CT &= ~(1 << (FREQ_GEN_CT_CH0_EN+ch));

}

/* ------------------------------------------------------------

 * INFO Disable all programmable frequency outputs

 * ------------------------------------------------------------ */

void neo430_freq_gen_disable(void) {

  register uint16_t ct = FREQ_GEN_CT;

  ct &= ~(1 << FREQ_GEN_CT_CH0_EN);

  ct &= ~(1 << FREQ_GEN_CT_CH1_EN);

  ct &= ~(1 << FREQ_GEN_CT_CH2_EN);

  FREQ_GEN_CT = ct;

}

/* ------------------------------------------------------------

 * INFO Disable all programmable frequency outputs and reset unit

 * ------------------------------------------------------------ */

void neo430_freq_gen_reset(void) {

  FREQ_GEN_CT = 0;

}

/* ------------------------------------------------------------

 * INFO Set frequency programmable frequency output

 * INFO f_out = ((f_cpu / nco_prsc) * tuning_word[15:0]) / 2^17

 * WARNING Imprecise due to rounding/truncation errors!

 * PARAM ch channel to configure (0..2)

 * PARAM frequency: output frequency in Hz (no fractions possible here)

 * RETURN the actual output frequency

 * ------------------------------------------------------------ */

uint32_t neo430_freq_gen_set_freq(uint16_t ch, uint32_t frequency) {

  // tuning_word = (f_out * 2^17) / (f_cpu / nco_prsc)

  uint32_t f_cpu = CLOCKSPEED_32bit;

  int16_t i;

  uint16_t prsc_shift = 12; // start with highest prescaler (4096 => 12)

  if (frequency > (f_cpu/4)) {

    return 0;

  }

  uint64_t freq_tmp;

  uint32_t freq_real;

  uint32_t freq_diff;

  uint32_t freq_diff_best = 0xffffffff; // max

  uint16_t tuning_word_best = 0;

  uint16_t prsc_best = 0;

  uint32_t freq_real_best = 0;

  // check all possible prescaler

  for(i=7; i>=0; i--) {

    freq_tmp = (uint64_t)frequency;

    freq_tmp = freq_tmp << (17 + prsc_shift); // multiply via bit shifts

    freq_tmp = freq_tmp / f_cpu;

    uint16_t tuning_word = (uint16_t)(freq_tmp);

    // add 1 to tuning word (for rounding issues)

    freq_real = neo430_freq_gen_nco_real_output(tuning_word+1, prsc_shift);

    freq_diff = freq_real - frequency;

    if ((int32_t)freq_diff < 0) {

      freq_diff = 0 - freq_diff;

    }

    // best result yet?

    if (freq_diff < freq_diff_best) {

      tuning_word_best = tuning_word;

      prsc_best = i;

      freq_diff_best = freq_diff;

      freq_real_best = freq_real;

    }

    // compute next prescaler

    if ((i == 5) || (i == 3)) {

      prsc_shift = prsc_shift - 3;

    }

    else {

      prsc_shift = prsc_shift - 1;

    }

  }

  // set tuning word and prescaler

  neo430_freq_gen_set(ch, tuning_word_best, prsc_best);

  return freq_real_best;

}

/* ------------------------------------------------------------

 * INFO Compute actual NCO output frequency based on tuning word and prescaler

 * RETURN the actual output frequency in Hz

 * ------------------------------------------------------------ */

static uint32_t neo430_freq_gen_nco_real_output(uint16_t tuning_word, uint16_t prsc_shift) {

  // f_out = ((f_cpu/nco_prsc) * tuning_word[15:0]) / 2^17

  uint32_t f_cpu = CLOCKSPEED_32bit;

  uint64_t f_out = (uint64_t)f_cpu;

  f_out = f_out * tuning_word;

  f_out = f_out >> (17 + prsc_shift); // divide by 2^17 * PRSC

  return (uint32_t)f_out;

}

/* ------------------------------------------------------------

 * INFO Set HW configuration

 * PARAM ch channel 0,1,2

 * PARAM 16-bit tuning word

 * PARAM 3-bit prescaler selector (0,...,7)

 * ------------------------------------------------------------ */

void neo430_freq_gen_set(uint16_t ch, uint16_t tuning_word, uint16_t prsc) {

  // set tuning word and prescaler

  register uint16_t ctrl = FREQ_GEN_CT;

  if (ch == 0) {

    FREQ_GEN_TW_CH0 = tuning_word;

    ctrl &= ~(0b111 << FREQ_GEN_CT_CH0_PRSC0); // clear old prescaler config

    ctrl |=  (prsc  << FREQ_GEN_CT_CH0_PRSC0); // set new prescaler config

  }

  else if (ch == 1) {

    FREQ_GEN_TW_CH1 = tuning_word;

    ctrl &= ~(0b111 << FREQ_GEN_CT_CH1_PRSC0); // clear old prescaler config

    ctrl |=  (prsc  << FREQ_GEN_CT_CH1_PRSC0); // set new prescaler config

  }

  else if (ch == 2) {

    FREQ_GEN_TW_CH2 = tuning_word;

    ctrl &= ~(0b111 << FREQ_GEN_CT_CH2_PRSC0); // clear old prescaler config

    ctrl |=  (prsc  << FREQ_GEN_CT_CH2_PRSC0); // set new prescaler config

  }

  FREQ_GEN_CT = ctrl;

}