set sample frequency

buttons.h

@@ -27,8 +27,8 @@
 #define BUTTON_AUTOREPEAT_INITIAL 100   // how many samples must read pressed before autorepeat starts
 #define BUTTON_AUTOREPEAT_NEXT 10       // how many samples must read pressed before the next repetition
 
-#define JOYSTICK_UPPER_PRESS_THRESHOLD 2100     // above this ADC value, button is pressed
-#define JOYSTICK_UPPER_RELEASE_THRESHOLD 2000   // below this ADC value, button is released
+#define JOYSTICK_UPPER_PRESS_THRESHOLD 2200     // above this ADC value, button is pressed
+#define JOYSTICK_UPPER_RELEASE_THRESHOLD 2100   // below this ADC value, button is released
 #define JOYSTICK_LOWER_PRESS_THRESHOLD 1700      // below this ADC value, button is pressed
 #define JOYSTICK_LOWER_RELEASE_THRESHOLD 1800   // above this ADC value, button is released
 

main.c

@@ -49,6 +49,20 @@ const float gVoltageScale[VOLTAGE_SCALES] = {
     0.1, 0.2, 0.5, 1., 2.
 };
 
+#define TIME_SCALES 6
+const char * const gTimeScaleStr[TIME_SCALES] = {
+"100 ms", "50 ms", "20 ms", " 10 ms", "50 us", "20 us"
+};
+
+const uint64_t gTImeScale[TIME_SCALES] = {
+    100 * 1000 / PIXELS_PER_DIV,
+    50 * 1000 / PIXELS_PER_DIV,
+    20 * 1000 / PIXELS_PER_DIV,
+    10 * 1000 / PIXELS_PER_DIV,
+    50 / PIXELS_PER_DIV,
+    20 / PIXELS_PER_DIV,
+};
+
 uint32_t cputime_unloaded;
 
 int Trigger(bool rising);
@@ -129,6 +143,7 @@ int main(void) {
     IntMasterEnable();
 
     uint8_t voltage_scale = 0;
+    uint8_t time_scale = 0;
     uint8_t rising = 1;
 
     while (true) {
@@ -154,6 +169,14 @@ int main(void) {
                 case Down: // previous scale
                     voltage_scale = (voltage_scale + VOLTAGE_SCALES - 1) % VOLTAGE_SCALES;
                     break;
+                case Right: // next scale
+                    time_scale = (time_scale + 1) % TIME_SCALES;
+                    set_frequency(gTImeScale[time_scale]);
+                    break;
+                case Left: // previous scale
+                    time_scale = (time_scale + TIME_SCALES - 1) % TIME_SCALES;
+                    set_frequency(gTImeScale[time_scale]);
+                    break;
             }
         }
 
@@ -176,6 +199,7 @@ int main(void) {
         // info
         GrContextForegroundSet(&sContext, ClrWheat);
         GrStringDraw(&sContext, gVoltageScaleStr[voltage_scale], /*length*/ -1, /*x*/ 0, /*y*/ 0, /*opaque*/ false);
+        GrStringDraw(&sContext, gTimeScaleStr[time_scale], /*length*/ -1, /*x*/ 60, /*y*/ 0, /*opaque*/ false);
         snprintf(str, sizeof(str), "CPU Load %.1f%%", usage_percent); 
         GrStringDraw(&sContext, str, /*length*/ -1, /*x*/ 0, /*y*/ HEIGHT - 10, /*opaque*/ false);
 

sampling.c

@@ -6,6 +6,7 @@
 #include "driverlib/gpio.h"
 #include "driverlib/sysctl.h"
 #include "driverlib/interrupt.h"
+#include "driverlib/timer.h"
 #include "sysctl_pll.h"
 #include "inc/hw_types.h"
 #include "inc/hw_memmap.h"
@@ -13,6 +14,8 @@
 #include "buttons.h"
 #include "sampling.h"
 
+extern uint32_t gSystemClock;   // [Hz] system clock frequency
+
 // latest sample index
 void ADC_ISR(void)
 {
@@ -41,6 +44,9 @@ void start_sampler() {
     // initialize ADC peripherals
     SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
     SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC1);
+
+    // timer for low-speed
+    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER2);
     // ADC clock
     uint32_t pll_frequency = SysCtlFrequencyGet(CRYSTAL_FREQUENCY);
     uint32_t pll_divisor =
@@ -64,3 +70,25 @@ void start_sampler() {
     // enable ADC1 sequence 0 interrupt in int. controller
     IntEnable(INT_ADC1SS0);
 }
+
+void set_frequency(uint64_t microseconds) {
+    if (microseconds == 1) {
+        ADCSequenceDisable(ADC1_BASE, 0);
+        // don't use a timer for high speed
+        ADCSequenceConfigure(ADC1_BASE, 0, ADC_TRIGGER_ALWAYS, 0);
+        ADCSequenceEnable(ADC1_BASE, 0);
+        return;
+    }
+
+    // initialize timer 2 in periodic mode
+    TimerDisable(TIMER2_BASE, TIMER_BOTH);
+    TimerConfigure(TIMER2_BASE, TIMER_CFG_PERIODIC);
+    #define MICROSECONDS_PER_SECOND 1000000
+    TimerLoadSet(TIMER2_BASE, TIMER_A, (uint32_t) ((uint64_t) gSystemClock * microseconds / MICROSECONDS_PER_SECOND) - 1);
+    TimerControlTrigger(TIMER2_BASE, TIMER_A, true);
+    TimerEnable(TIMER2_BASE, TIMER_A);
+
+    ADCSequenceDisable(ADC1_BASE, 0);
+    ADCSequenceConfigure(ADC1_BASE, 0, ADC_TRIGGER_TIMER, 0);
+    ADCSequenceEnable(ADC1_BASE, 0);
+}

sampling.h

@@ -15,4 +15,6 @@ volatile uint32_t gADCErrors; // number of missed ADC deadlines
 // initialize ADC and ISR
 void start_sampler(void);
 
+void set_frequency(uint64_t microseconds);
+
 #endif /* SAMPLING_H_ */