Hello
On 11/09/2016 05:44 PM, Ramesh Shanmugasundaram wrote:
+static int max2175_set_lo_freq(struct max2175 *ctx, u64 lo_freq)
+{
+ u64 scaled_lo_freq, scaled_npf, scaled_integer, scaled_fraction;
+ u32 frac_desired, int_desired, lo_mult = 1;
+ const u32 scale_factor = 1000000U;
+ u8 loband_bits = 0, vcodiv_bits = 0;
+ enum max2175_band band;
+ int ret;
+
+ /* Scale to larger number for precision */
+ scaled_lo_freq = lo_freq * scale_factor * 100;
+ band = max2175_read_bits(ctx, 5, 1, 0);
+
+ mxm_dbg(ctx, "set_lo_freq: scaled lo_freq %llu lo_freq %llu band %d\n",
+ scaled_lo_freq, lo_freq, band);
+
+ switch (band) {
+ case MAX2175_BAND_AM:
+ if (max2175_read_bit(ctx, 5, 7) == 0)
+ lo_mult = 16;
else is lo_mult = 1. No idea if it is correct, but sounds very small
output divider for low freq like am band. And on the other-hand local
oscillator output divider, which I expect this to be, is usually 2 or more.
+ break;
+ case MAX2175_BAND_FM:
+ if (lo_freq <= 74700000) {
+ lo_mult = 16;
No meaning as you set it later 8.
+ } else if (lo_freq > 74700000 && lo_freq <= 110000000) {
+ loband_bits = 1;
+ } else {
+ loband_bits = 1;
+ vcodiv_bits = 3;
+ }
+ lo_mult = 8;
+ break;
+ case MAX2175_BAND_VHF:
+ if (lo_freq <= 210000000) {
+ loband_bits = 2;
+ vcodiv_bits = 2;
+ } else {
+ loband_bits = 2;
+ vcodiv_bits = 1;
+ }
+ lo_mult = 4;
+ break;
+ default:
+ loband_bits = 3;
+ vcodiv_bits = 2;
+ lo_mult = 2;
+ break;
+ }
+
+ if (band == MAX2175_BAND_L)
+ scaled_npf = div_u64(div_u64(scaled_lo_freq, ctx->xtal_freq),
+ lo_mult);
+ else
+ scaled_npf = div_u64(scaled_lo_freq, ctx->xtal_freq) * lo_mult;
+
+ scaled_npf = div_u64(scaled_npf, 100);
+ scaled_integer = div_u64(scaled_npf, scale_factor) * scale_factor;
+ int_desired = div_u64(scaled_npf, scale_factor);
+ scaled_fraction = scaled_npf - scaled_integer;
+ frac_desired = div_u64(scaled_fraction << 20, scale_factor);
+
+ /* Check CSM is not busy */
+ ret = max2175_poll_csm_ready(ctx);
+ if (ret)
+ return ret;
+
+ mxm_dbg(ctx, "loband %u vcodiv %u lo_mult %u scaled_npf %llu\n",
+ loband_bits, vcodiv_bits, lo_mult, scaled_npf);
+ mxm_dbg(ctx, "scaled int %llu frac %llu desired int %u frac %u\n",
+ scaled_integer, scaled_fraction, int_desired, frac_desired);
+
+ /* Write the calculated values to the appropriate registers */
+ max2175_write(ctx, 1, int_desired);
+ max2175_write_bits(ctx, 2, 3, 0, (frac_desired >> 16) & 0xf);
+ max2175_write(ctx, 3, frac_desired >> 8);
+ max2175_write(ctx, 4, frac_desired);
+ max2175_write_bits(ctx, 5, 3, 2, loband_bits);
+ max2175_write_bits(ctx, 6, 7, 6, vcodiv_bits);
+ return ret;
+}
That synthesizer config is hard to understand. It seems to be
fractional-N, with configurable N, K and output divider - like a school
book example.
+----------------------------+
v |
Fref +----+ +-------+ +------+
------> | PD | --> | VCO | ------> | /N.F |
+----+ +-------+ +------+
|
|
v
+-------+ Fout
| /Rout | ------>
+-------+
I made following look-up table in order to understand it:
band lo freq band vcodiv div_out
AM < 50000000 0 0 16 // reg 5 bit 7 ?
FM < 74700000 0 0 16
FM < 110000000 1 0 8
FM < 160000000 1 3 8
VHF < 210000000 2 2 4
VHF < 600000000 2 1 4
L <2000000000 3 2 2
"vcodiv" looks unrelated to synth calculation, dunno what it is.
One which makes calculation very complex looking is that it is based of
floating point calculus. On integer mathematics you should replace
fractional part with fractional modulus (usually letter "K" is used for
fractional modulus on PLL calc).
So that ends up something like:
1) select suitable lo output divider from desired output frequency
2) calculate vco frequency
3) convert vco frequency to N and K
* N = Fvco/Fref
* K = Fvco%Fref
4) convert K to control word (looks like << 20)
5) program values
Result should be calculus without scaling.
regards
Antti
--
http://palosaari.fi/
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