Пример #1
0
/* set frequency of PWM signal to freq */
int pwm_freq_set(int channel, u_int32_t freq)
{
	/* in order to get maximum resolution, the pre-scaler must be set to
	 * something like freq << 16.  However, the mimimum pre-scaled frequency
	 * we can get is MCLK (48MHz), the minimum is MCLK/(1024*255) =
	 * 48MHz/261120 = 183Hz */
	u_int32_t overall_div;
	u_int32_t presc_total;
	u_int8_t cpre = 0;
	u_int16_t cprd;

	if (freq > MCLK)
		return -ERANGE;
	
	overall_div = MCLK / freq;
	DEBUGPCRF("mclk=%u, freq=%u, overall_div=%u", MCLK, freq, overall_div);

	if (overall_div > 0x7fff) {
		/* divisor is larger than half the maximum CPRD register, we
		 * have to configure prescalers */
		presc_total = overall_div >> 15;

		/* find highest 2^n fitting in prescaler (highest bit set) */
		cpre = fhs(presc_total);
		if (cpre > 0) {
			/* subtract one, because of fhs semantics */
			cpre--;
		}
		cprd = overall_div / (1 << cpre);
	} else
Пример #2
0
/* set frequency of PWM signal to freq */
int pwmFreqSet(int channel, uint32_t freq)
{
    /* in order to get maximum resolution, the pre-scaler must be set to
     * something like freq << 16.  However, the mimimum pre-scaled frequency
     * we can get is MCLK (48MHz), the minimum is MCLK/(1024*255) =
     * 48MHz/261120 = 183Hz */
    uint32_t overall_div;
    uint32_t presc_total;
    uint8_t cpre = 0;
    uint16_t cprd;

    if (freq > MCK)
        return -1;
    overall_div = MCK / freq;

    if (overall_div > 0x7fff)
    {
        // divisor is larger than half the maximum CPRD register, we
        // have to configure prescalers
        presc_total = overall_div >> 15;
        // find highest 2^n fitting in prescaler (highest bit set)
        cpre = fhs(presc_total);
        if (cpre > 0)
        {
            // subtract one, because of fhs semantics //
            cpre--;
        }
        cprd = overall_div / (1 << cpre);
    }