icE1usb fw: Add GPSDO VCXO trimming loop
Rather basic and not super well tested, use with caution Signed-off-by: Sylvain Munaut <tnt@246tNt.com> Change-Id: I5f9ce6621492be967d6a44d31f270e107f3ef686
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70c10f05cf
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e76b643298
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@ -49,6 +49,7 @@ HEADERS_app=\
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config.h \
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e1.h \
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gps.h \
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gpsdo.h \
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ice1usb_proto.h \
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misc.h \
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usb_desc_ids.h \
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@ -62,6 +63,7 @@ SOURCES_app=\
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e1.c \
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fw_app.c \
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gps.c \
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gpsdo.c \
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misc.c \
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usb_desc_app.c \
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usb_dev.c \
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@ -15,6 +15,7 @@
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#include "console.h"
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#include "e1.h"
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#include "gps.h"
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#include "gpsdo.h"
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#include "led.h"
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#include "misc.h"
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#include "mini-printf.h"
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@ -94,12 +95,13 @@ void main()
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pdm_set(PDM_E1_RX1, true, 128 + d, false);
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#endif
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/* Setup clock tuning */
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pdm_set(PDM_CLK_HI, true, 2048, false);
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pdm_set(PDM_CLK_LO, false, 0, false);
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/* GPS init */
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gps_init();
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#if defined(BOARD_ICE1USB_PROTO_ICEBREAKER) || defined(BOARD_ICE1USB_PROTO_BITSY)
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gpsdo_init(VCTXO_TAITIEN_VT40);
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#else
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gpsdo_init(VCTXO_SITIME_SIT3808_E);
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#endif
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/* Enable USB directly */
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usb_init(&app_stack_desc);
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@ -170,6 +172,7 @@ void main()
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/* GPS poll */
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gps_poll();
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gpsdo_poll();
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usb_gps_poll();
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}
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}
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@ -0,0 +1,254 @@
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/*
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* gpsdo.c
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*
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* Copyright (C) 2019-2022 Sylvain Munaut <tnt@246tNt.com>
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* SPDX-License-Identifier: GPL-3.0-or-later
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*/
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#include <stdint.h>
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#include <string.h>
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#include "console.h"
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#include "gps.h"
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#include "gpsdo.h"
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#include "misc.h"
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struct {
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/* Current tuning */
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struct {
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uint16_t coarse;
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uint16_t fine;
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} tune;
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/* Measurements */
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struct {
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uint32_t tick_prev; /* Previous tick value */
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uint32_t last; /* Last measurement */
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int skip; /* Number of measurement left to discard */
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int invalid; /* Number of consecutive invalid measurements */
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} meas;
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/* FSM */
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enum {
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STATE_DISABLED, /* Forced to manual */
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STATE_HOLD_OVER, /* GPS invalid data, hold */
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STATE_TUNE_COARSE, /* Adjust coarse tuning until we're +- 3 Hz */
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STATE_TUNE_FINE, /* Fine tracking */
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} state;
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/* Coarse tuning */
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struct {
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int vctxo_sensitivity;
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int step;
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} coarse;
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/* Fine tracking */
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struct {
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int acc;
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int div;
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} fine;
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} g_gpsdo;
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/* VCXTO sensitivity vs 'coarse' count for fast initial acquisition */
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/*
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* Note that the spec if often a guaranteed minimum range and goes
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* from ~0.1V to 3.2V instead of 0-3.3V so actual sensitivity is
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* higher than the "theoritical value". We boost it by ~ 10% here.
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*/
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static const int
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vctxo_sensitivity[] = {
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/* +- 50 ppm pull range => ~ 0.75 Hz / hi-count (set to 0.85) */
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[VCTXO_TAITIEN_VT40] = 300,
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/* +- 100 ppm pull range => ~ 1.50 Hz / hi-count (set to 1.6) */
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[VCTXO_SITIME_SIT3808_E] = 160,
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};
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/* Tuning params */
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#define TARGET 30720000
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#define MAX_DEV_VALID 1000
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#define MAX_DEV_FINE 3
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#define MAX_INVALID 5
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static void
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_gpsdo_coarse_start(void)
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{
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/* Set the state */
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g_gpsdo.state = STATE_TUNE_COARSE;
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/* Skip a few measurements to be safe */
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g_gpsdo.meas.skip = 3;
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/* Reset coarse tuning state */
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g_gpsdo.coarse.step = 0;
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/* Put the fine adjust back in the middle point */
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g_gpsdo.tune.coarse += ((int)g_gpsdo.tune.fine - 2048) >> 6;
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g_gpsdo.tune.fine = 2048;
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pdm_set(PDM_CLK_HI, true, g_gpsdo.tune.coarse, false);
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pdm_set(PDM_CLK_LO, true, g_gpsdo.tune.fine, false);
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}
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static void
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_gpsdo_fine_start(void)
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{
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/* Set the state */
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g_gpsdo.state = STATE_TUNE_FINE;
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/* Reset the long term error tracking */
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g_gpsdo.fine.acc = 0;
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g_gpsdo.fine.div = 0;
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}
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static void
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_gpsdo_coarse_tune(uint32_t tick_diff)
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{
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int freq_diff = (int)tick_diff - TARGET;
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/* Is the measurement good enough to switch to fine ? */
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if ((freq_diff > -MAX_DEV_FINE) && (freq_diff < MAX_DEV_FINE)) {
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_gpsdo_fine_start();
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return;
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}
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/* Estimate correction and apply it */
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g_gpsdo.tune.coarse -= (freq_diff * g_gpsdo.coarse.vctxo_sensitivity) >> 8;
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pdm_set(PDM_CLK_HI, true, g_gpsdo.tune.coarse, false);
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/* Skip next measurement */
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g_gpsdo.meas.skip = 1;
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/* Debug */
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#ifdef GPSDO_DEBUG
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printf("[+] GPSDO Coarse: err=%d tune=%d\n", freq_diff, g_gpsdo.tune.coarse);
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#endif
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}
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static void
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_gpsdo_fine_track(uint32_t tick_diff)
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{
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int freq_diff = (int)tick_diff - TARGET;
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uint16_t tune;
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/* Did we deviate too much ? */
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if ((freq_diff < -2*MAX_DEV_FINE) && (freq_diff > 2*MAX_DEV_FINE)) {
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_gpsdo_coarse_start();
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return;
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}
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/* Accumulate long term error */
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g_gpsdo.fine.acc += freq_diff;
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/* Update fine tuning value */
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if (((g_gpsdo.fine.acc >= 0) && (freq_diff > 0)) ||
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((g_gpsdo.fine.acc <= 0) && (freq_diff < 0)))
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{
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g_gpsdo.tune.fine -= freq_diff;
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}
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if (g_gpsdo.fine.acc) {
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if (++g_gpsdo.fine.div > 10) {
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g_gpsdo.fine.div = 0;
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if (g_gpsdo.fine.acc > 0)
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g_gpsdo.tune.fine--;
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else if (g_gpsdo.fine.acc < 0)
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g_gpsdo.tune.fine++;
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}
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} else {
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g_gpsdo.fine.div = 0;
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}
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/* Apply value with a bias from long term accumulator */
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tune = g_gpsdo.tune.fine - (g_gpsdo.fine.acc / 2);
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pdm_set(PDM_CLK_LO, true, tune, false);
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/* Debug */
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#ifdef GPSDO_DEBUG
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printf("[+] GPSDO Fine: err=%d acc=%d tune=%d\n", freq_diff, g_gpsdo.fine.acc, g_gpsdo.tune.fine);
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#endif
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}
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void
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gpsdo_poll(void)
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{
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uint32_t tick_now, tick_diff;
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bool valid;
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/* Get current tick and check if there was a PPS and estimate frequency */
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tick_now = time_pps_read();
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if (tick_now == g_gpsdo.meas.tick_prev)
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return;
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g_gpsdo.meas.last = tick_diff = tick_now - g_gpsdo.meas.tick_prev;
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g_gpsdo.meas.tick_prev = tick_now;
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/* If we're currently discarding samples, skip it */
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if (g_gpsdo.meas.skip) {
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g_gpsdo.meas.skip--;
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return;
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}
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/* If we're disabled, nothing else to do */
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if (g_gpsdo.state == STATE_DISABLED)
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return;
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/* Check GPS state */
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if (!gps_has_valid_fix()) {
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/* No GPS fix, go to hold-over */
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g_gpsdo.state = STATE_HOLD_OVER;
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return;
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}
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/* Check measurement plausibility */
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valid = (tick_diff > (TARGET - MAX_DEV_VALID)) && (tick_diff < (TARGET + MAX_DEV_VALID));
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if (valid) {
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/* If we're in hold-over, switch to active */
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if (g_gpsdo.state == STATE_HOLD_OVER) {
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_gpsdo_coarse_start();
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return;
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}
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} else {
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/* Count invalid measurements and if too many of
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* them, we go back to hold-over */
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if (++g_gpsdo.meas.invalid >= MAX_INVALID) {
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g_gpsdo.state = STATE_HOLD_OVER;
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return;
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}
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}
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g_gpsdo.meas.invalid = 0;
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/* If we reach here, we have a valid fix, valid measurement and
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* we're not in hold-over or disabled. Feed the correct loop */
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if (g_gpsdo.state == STATE_TUNE_COARSE)
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_gpsdo_coarse_tune(tick_diff);
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else if (g_gpsdo.state == STATE_TUNE_FINE)
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_gpsdo_fine_track(tick_diff);
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}
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void
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gpsdo_init(enum gpsdo_vctxo_model vctxo)
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{
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/* State */
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memset(&g_gpsdo, 0x00, sizeof(g_gpsdo));
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/* Default tune to middle range */
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g_gpsdo.tune.coarse = 2048;
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g_gpsdo.tune.fine = 2048;
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pdm_set(PDM_CLK_HI, true, g_gpsdo.tune.coarse, false);
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pdm_set(PDM_CLK_LO, true, g_gpsdo.tune.fine, false);
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/* Initial state and config */
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g_gpsdo.state = STATE_HOLD_OVER;
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g_gpsdo.coarse.vctxo_sensitivity = vctxo_sensitivity[vctxo];
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}
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@ -0,0 +1,16 @@
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/*
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* gpsdo.h
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*
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* Copyright (C) 2019-2022 Sylvain Munaut <tnt@246tNt.com>
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* SPDX-License-Identifier: GPL-3.0-or-later
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*/
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#pragma once
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enum gpsdo_vctxo_model {
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VCTXO_TAITIEN_VT40 = 0, /* VTEUALJANF-30.720000 */
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VCTXO_SITIME_SIT3808_E = 1, /* SIT3808AI-D2-33EE-30.720000T */
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};
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void gpsdo_poll(void);
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void gpsdo_init(enum gpsdo_vctxo_model vctxo);
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