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Synchronise the dexcom collection times to reduce refresh lag

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When collecting date from Dexcom via share2bridge-dexcom
before we would poll at regular intervals.

Dexcom transmitters / apps refresh every 5 minutes give/take the inaccuracy in the transmitters clock.

If we poll every 5 minutes, we will randomly introduce up to 5 minutes of lag before we refresh.

For example, if we poll 4:59s after dexcom refreshed we will face a 4:59s lag seeing the latest data arrive

This patch introduces a refresh adjustment. We look at the timestamp of the most recent data item and aim to refresh
5 minutes plus a buffer after that timestamp.

for example, 5:20s after the most recent data time. the additional buffer gives dexcom a chance to push the data through their
application/infrastructure (after the app sends the data, it appears in testing to be around 20s before it is available in the API)

This reduces the lag time to a reliable 20 seconds regardless of when nightscout was started and keeps it in track as it drifts forwards and back.
This commit is contained in:
Chris Pitchford
2021-12-09 22:55:52 +00:00
parent 9b048dddb7
commit a34a58ba43
1 changed files with 43 additions and 4 deletions
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lib/plugins/bridge.js
+43 -4
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@@ -24,6 +24,7 @@ function bridged (entries) {
mostRecentRecord = glucose[i].date;
}
}
//console.log("DEXCOM: Most recent entry received; "+new Date(mostRecentRecord).toString());
}
entries.create(glucose, function stored (err) {
if (err) {
@@ -46,12 +47,12 @@ function options (env) {
, minutes: env.extendedSettings.bridge.minutes || 1440
};
var interval = env.extendedSettings.bridge.interval || 60000 * 2.5; // Default: 2.5 minutes
var interval = env.extendedSettings.bridge.interval || 60000 * 2.6; // Default: 2.6 minutes
if (interval < 1000 || interval > 300000) {
// Invalid interval range. Revert to default
console.error("Invalid interval set: [" + interval + "ms]. Defaulting to 2.5 minutes.")
interval = 60000 * 2.5 // 2.5 minutes
console.error("Invalid interval set: [" + interval + "ms]. Defaulting to 2.6 minutes.")
interval = 60000 * 2.6 // 2.6 minutes
}
return {
@@ -75,15 +76,53 @@ function create (env, bus) {
bridge.startEngine = function startEngine (entries) {
opts.callback = bridged(entries);
let last_run = new Date(0).getTime();
let last_ondemand = new Date(0).getTime();
function should_run() {
// Time we expect to have to collect again
const msRUN_AFTER = (300+20) * 1000;
const msNow = new Date().getTime();
const next_entry_expected = mostRecentRecord + msRUN_AFTER;
if (next_entry_expected > msNow) {
// we're not due to collect a new slot yet. Use interval
const ms_since_last_run = msNow - last_run;
if (ms_since_last_run < interval) {
return false;
}
last_run = msNow;
last_ondemand = new Date(0).getTime();
console.log("DEXCOM: Running poll");
return true;
}
const ms_since_last_run = msNow - last_ondemand;
if (ms_since_last_run < interval) {
return false;
}
last_run = msNow;
last_ondemand = msNow;
console.log("DEXCOM: Data due, running extra poll");
return true;
}
let timer = setInterval(function () {
if (!should_run()) return;
opts.fetch.minutes = parseInt((new Date() - mostRecentRecord) / 60000);
opts.fetch.maxCount = parseInt((opts.fetch.minutes / 5) + 1);
opts.firstFetchCount = opts.fetch.maxCount;
console.log("Fetching Share Data: ", 'minutes', opts.fetch.minutes, 'maxCount', opts.fetch.maxCount);
engine(opts);
}, interval);
}, 1000 /*interval*/);
if (bus) {
bus.on('teardown', function serverTeardown () {