Add startMicros to LowLatencyLogger

LowLatencyLoggerADXL345/LowLatencyLoggerADXL345.ino

 #include "SdFat.h"
 #include "FreeStack.h"
 //------------------------------------------------------------------------------
-// User data functions.  Modify these functions for your data items.
-#include "UserDataType.h"  // Edit this include file to change data_t.
-
 // Set useSharedSpi true for use of an SPI sensor.
 const bool useSharedSpi = true;
 
+// File start time in micros.
+uint32_t startMicros;
+//------------------------------------------------------------------------------
+// User data functions.  Modify these functions for your data items.
+#include "UserDataType.h"  // Edit this include file to change data_t.
+
 const uint8_t ADXL345_CS = 9;
 
 const uint8_t POWER_CTL = 0x2D;  //Power Control Register
 
 // Print a data record.
 void printData(Print* pr, data_t* data) {
-  pr->print(data->time);
+  pr->print(data->time - startMicros);
   for (int i = 0; i < ACCEL_DIM; i++) {
     pr->write(',');
     pr->print(data->accel[i]);
   // Wait for Serial Idle.
   Serial.flush();
   delay(10);
+  bool closeFile = false;
   uint32_t bn = 0;
   uint32_t t0 = millis();
   uint32_t t1 = t0;
   uint32_t maxDelta = 0;
   uint32_t minDelta = 99999;
   uint32_t maxLatency = 0;
-  
-  // Start at a multiple of interval.
-  uint32_t logTime = micros()/LOG_INTERVAL_USEC + 1;
-  logTime *= LOG_INTERVAL_USEC;
-  bool closeFile = false;
+  uint32_t logTime = micros();
+
+  // Set time for first record of file.
+  startMicros = logTime + LOG_INTERVAL_USEC;
+
   while (1) {
     // Time for next data record.
     logTime += LOG_INTERVAL_USEC;

SdFat/examples/LowLatencyLogger/LowLatencyLogger.ino

 #include "SdFat.h"
 #include "FreeStack.h"
 //------------------------------------------------------------------------------
-// User data functions.  Modify these functions for your data items.
-#include "UserDataType.h"  // Edit this include file to change data_t.
-
 // Set useSharedSpi true for use of an SPI sensor.
 const bool useSharedSpi = false;
 
+// File start time in micros.
+uint32_t startMicros;
+//------------------------------------------------------------------------------
+// User data functions.  Modify these functions for your data items.
+#include "UserDataType.h"  // Edit this include file to change data_t.
+
 // Acquire a data record.
 void acquireData(data_t* data) {
   data->time = micros();
 
 // Print a data record.
 void printData(Print* pr, data_t* data) {
-  pr->print(data->time);
+  pr->print(data->time - startMicros);
   for (int i = 0; i < ADC_DIM; i++) {
     pr->write(',');
     pr->print(data->adc[i]);
   // Wait for Serial Idle.
   Serial.flush();
   delay(10);
+  bool closeFile = false;
   uint32_t bn = 0;
   uint32_t t0 = millis();
   uint32_t t1 = t0;
   uint32_t maxDelta = 0;
   uint32_t minDelta = 99999;
   uint32_t maxLatency = 0;
-  
-  // Start at a multiple of interval.
-  uint32_t logTime = micros()/LOG_INTERVAL_USEC + 1;
-  logTime *= LOG_INTERVAL_USEC;
-  bool closeFile = false;
+  uint32_t logTime = micros();
+
+  // Set time for first record of file.
+  startMicros = logTime + LOG_INTERVAL_USEC;
+
   while (1) {
     // Time for next data record.
     logTime += LOG_INTERVAL_USEC;