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Populate transmit timestamp in request and verify the originate timestamp in the response matches. #28

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Populate transmit timestamp in request and verify the originate timestamp in the response matches. #28

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21 changes: 18 additions & 3 deletions NTP.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -73,8 +73,17 @@ bool NTP::update() {
}

bool NTP::ntpUpdate() {
if (server == nullptr) udp->beginPacket(serverIP, NTP_PORT);
if (server == nullptr) udp->beginPacket(serverIP, NTP_PORT);
else udp->beginPacket(server, NTP_PORT);
// We set the transmit timestamp to be able to pick the
// correct response packet in case of previous responses arriving
// later. Sine the transmit timestamp is just copied verbatim
// into the response origin timestamp but otherwise not used
// it can be any number, and in particular does not nned to be
// an ntp-style timestamp.
const int64_t transmit_ts = micros();
// Set transmit ts, offset in packet is 40, i.e. 10 32-bit words
*reinterpret_cast<int64_t *>(ntpRequest + 10*4) = transmit_ts;
udp->write(ntpRequest, NTP_PACKET_SIZE);
udp->endPacket();
uint8_t timeout = 0;
Expand All @@ -84,9 +93,15 @@ bool NTP::ntpUpdate() {
size = udp->parsePacket();
if (timeout > 100) return false;
timeout++;
} while (size != 48);
if (size == 48) {
udp->read(ntpQuery, NTP_PACKET_SIZE);
}
} while (size != 48 ||
// Check returned originate timestamp also matches
// transmit_ts. Originate timestamp is 6 32 bit words
// into packet.
*reinterpret_cast<int64_t *>(ntpQuery + 6*4) != transmit_ts);
lastUpdate = millis() - (10 * (timeout + 1));
udp->read(ntpQuery, NTP_PACKET_SIZE);
#ifdef __AVR__
unsigned long highWord = word(ntpQuery[40], ntpQuery[41]);
unsigned long lowWord = word(ntpQuery[42], ntpQuery[43]);
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4 changes: 2 additions & 2 deletions NTP.h
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Expand Up @@ -249,8 +249,8 @@ class NTP {
UDP *udp;
const char* server = nullptr;
IPAddress serverIP;
uint8_t ntpRequest[NTP_PACKET_SIZE]; // = {0xE3, 0x00, 0x06, 0xEC};
uint8_t ntpQuery[NTP_PACKET_SIZE];
uint8_t ntpRequest[NTP_PACKET_SIZE] __attribute__((aligned(4))); // = {0xE3, 0x00, 0x06, 0xEC};
uint8_t ntpQuery[NTP_PACKET_SIZE] __attribute__((aligned(4)));
time_t utcCurrent = 0;
time_t local = 0;
struct tm *current;
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