# HG changeset patch
# User František Kučera <franta-hg@frantovo.cz>
# Date 1497143127 -7200
# Node ID e1e5db678ce841bfc69e4b34603bbdbe935e3cf3
# Parent  254d5d1bc659b2295b51b91dbbca50992426a910
lpt-signal-generator: calibration

diff -r 254d5d1bc659 -r e1e5db678ce8 c++/lpt-signal-generator/lpt.cpp
--- a/c++/lpt-signal-generator/lpt.cpp	Sun Jun 11 01:25:56 2017 +0200
+++ b/c++/lpt-signal-generator/lpt.cpp	Sun Jun 11 03:05:27 2017 +0200
@@ -54,10 +54,14 @@
    */
   setlocale(LC_ALL,"");
 
+
+  // configuration ----
   int addr = 0xe400; // parallel port address; first number of given port in: cat /proc/ioports | grep parport
   int baseFreq = 10000; // base frequency in Hz, should be between 5 000 between 10 000 Hz; lower frequency leads to dashed/dotted lines instead of greyscale
   int outputPower = 20; // duty cycle; 100 = 100 %
   int duration = 1; // in seconds; total sleep time, see note above
+  // ------------------
+
 
   int valueWidth =  10; // just for padding of printed values
   int labelWidth = -15; // just for padding of printed labels
@@ -74,9 +78,6 @@
   int timeOn =  oneSecond *        outputPower  / 100 / baseFreq;
   int timeOff = oneSecond * (100 - outputPower) / 100 / baseFreq;
 
-  timeOn  -= 13;
-  timeOff -= 13;
-
   int cycleCount = duration * baseFreq;
   wprintf(L"%*ls %'*d ×\n", labelWidth, L"Cycle count:", valueWidth, cycleCount);
   wprintf(L"%*ls %'*d μs 1× in each cycle\n", labelWidth, L"Time on:",  valueWidth, timeOn);
@@ -84,12 +85,67 @@
 
   //wprintf(L"%*ls %*ls\n", labelWidth, L"unicode test:", valueWidth, L"čeština → …");
 
+  wprintf(L"\n");
 
   if (ioperm(addr,1,1)) { fwprintf(stderr, L"Access denied to port %#x\n", addr), exit(1); }
 
-  outb(0b00000000, addr);
 
+  // calibration
   auto startTimestamp = chrono::high_resolution_clock::now();
+  auto calibrationCycles = 10000;
+  auto calibrationSleepTime = 10;
+
+  for (int i = 0; i < calibrationCycles; i++) {
+    outb(0b00000000, addr);
+    usleep(calibrationSleepTime);
+    outb(0b00000000, addr);
+    usleep(calibrationSleepTime);
+  }
+
+  auto finishTimestamp = chrono::high_resolution_clock::now();
+  auto measuredDuration = chrono::duration_cast<chrono::nanoseconds>(finishTimestamp - startTimestamp).count();
+
+  auto singleOutbCostNano = (measuredDuration - calibrationCycles*2*calibrationSleepTime*1000)/calibrationCycles/2;
+  auto singleOutbCostMicro = singleOutbCostNano/1000;
+
+  wprintf(L"%*ls %'*d μs 2× in each calibration cycle\n", labelWidth, L"Single outb():", valueWidth, singleOutbCostMicro);
+  wprintf(L"%*ls %'*d ns 2× in each calibration cycle\n", labelWidth, L"Single outb():", valueWidth, singleOutbCostNano);
+
+  auto minPower = 100*singleOutbCostNano/(1000*1000*1000/baseFreq);
+  auto maxPower = 100-minPower;
+  wprintf(L"%*ls %*d %% feasible duty cycle\n",  labelWidth, L"Minimum power:", valueWidth, minPower);
+  wprintf(L"%*ls %*d %% feasible duty cycle\n",  labelWidth, L"Maximum power:", valueWidth, maxPower);
+
+  if (singleOutbCostMicro < timeOn && singleOutbCostMicro < timeOff) {
+    wprintf(L"%*ls %*ls both frequency and duty cycle should be correct\n",  labelWidth, L"Calibration:", valueWidth, L"OK");
+    timeOn  -= singleOutbCostMicro;
+    timeOff -= singleOutbCostMicro;
+  } else if (2*singleOutbCostMicro < (timeOn + timeOff)) {
+    wprintf(L"%*ls %*ls frequency should be OK, but duty cycle is not feasible\n",  labelWidth, L"Calibration:", valueWidth, L"WARNING");
+    timeOn  -= singleOutbCostMicro;
+    timeOff -= singleOutbCostMicro;
+
+    if (timeOn < 0) {
+      timeOff -= timeOn;
+      timeOn = 0;
+    } else {
+      timeOn -= timeOff;
+      timeOff = 0;
+    }
+  } else {
+    wprintf(L"%*ls %*ls both frequency and duty cycle are not feasible\n",  labelWidth, L"Calibration:", valueWidth, L"ERROR");
+    timeOn  = 0;
+    timeOff = 0;
+  }
+
+  wprintf(L"%*ls %'*d μs 1× in each cycle\n", labelWidth, L"Sleep on:",  valueWidth, timeOn);
+  wprintf(L"%*ls %'*d μs 1× in each cycle\n", labelWidth, L"Sleep off:", valueWidth, timeOff);
+
+  wprintf(L"\n");
+
+
+  // actual signal generation
+  startTimestamp = chrono::high_resolution_clock::now();
 
   for (int i = 0; i < cycleCount; i++) {
     outb(0b00000001, addr); // first data out pin = data out 0 = pin 2 on DB-25 connector
@@ -98,10 +154,10 @@
     usleep(timeOff);
   }
 
-  auto finishTimestamp = chrono::high_resolution_clock::now();
-  auto measuredDuration = chrono::duration_cast<chrono::nanoseconds>(finishTimestamp - startTimestamp).count();
+  finishTimestamp = chrono::high_resolution_clock::now();
+  measuredDuration = chrono::duration_cast<chrono::nanoseconds>(finishTimestamp - startTimestamp).count();
 
-  wprintf(L"%*ls %'*d μs 2× in each cycle\n", labelWidth, L"single outb():", valueWidth, (measuredDuration-duration*oneSecond*1000)/cycleCount/2/1000);
-  wprintf(L"%*ls %'*d ns 2× in each cycle\n", labelWidth, L"single outb():", valueWidth, (measuredDuration-duration*oneSecond*1000)/cycleCount/2);
+  wprintf(L"%*ls %'*d μs in total\n", labelWidth, L"Deviation:", valueWidth, (measuredDuration-duration*oneSecond*1000)/1000);
+  wprintf(L"%*ls %'*d ns in each cycle\n", labelWidth, L"Deviation:", valueWidth, (measuredDuration-duration*oneSecond*1000)/cycleCount);
 
 }