Introduce PWM freq switching so that power could be averaged on shorter intervals

With this a TS-I tip is usable with a small netbook 19 V / 30 W PSU with
power limit set to 40 W (38.9 W is reported during the heating up
stage). Without this the device just reboots on attempt to turn on the
heater (unless the power limit is set to 10 or even 5 W).

This code doesn't affect maximum power available and allows up to 73 W
when a beefy 24 V / 96 W PSU is used.

Should be useful for all models, not just TS100.

The fixed comments are based on calculations, not measurements!

Fixes #693.

workspace/TS100/Core/BSP/BSP.h

@@ -1,9 +1,10 @@
+#include <stdint.h>
+#include <stdbool.h>
 #include "BSP_Flash.h"
 #include "BSP_Power.h"
 #include "BSP_QC.h"
 #include "Defines.h"
 #include "Model_Config.h"
-#include "stdint.h"
 /*
  * BSP.h -- Board Support
  *
@@ -16,11 +17,19 @@
 extern "C" {
 #endif
 
+// maximum htim2 PWM value
+extern const uint16_t powerPWM;
+// htim2.Init.Period, the full PWM cycle
+extern uint16_t totalPWM;
+
 // Called first thing in main() to init the hardware
 void preRToSInit();
 // Called once the RToS has started for any extra work
 void postRToSInit();
 
+// Called once from preRToSInit()
+void BSPInit(void);
+
 // Called to reset the hardware watchdog unit
 void resetWatchdog();
 // Accepts a output level of 0.. to use to control the tip output PWM
@@ -31,6 +40,9 @@ uint16_t getHandleTemperature();
 uint16_t getTipRawTemp(uint8_t refresh);
 // Returns the main DC input voltage, using the adjustable divisor + sample flag
 uint16_t getInputVoltageX10(uint16_t divisor, uint8_t sample);
+// Switch to the most suitable PWM freq given the desired period;
+// returns true if the switch was performed and totalPWM changed
+bool tryBetterPWM(uint8_t pwm);
 
 // Readers for the two buttons
 // !! Returns 1 if held down, 0 if released

workspace/TS100/Core/BSP/Miniware/BSP.cpp

@@ -12,6 +12,14 @@
 volatile uint16_t PWMSafetyTimer = 0;
 volatile uint8_t pendingPWM = 0;
 
+const uint16_t powerPWM = 255;
+static const uint8_t holdoffTicks = 13; // delay of 7 ms
+static const uint8_t tempMeasureTicks = 17;
+
+uint16_t totalPWM; //htim2.Init.Period, the full PWM cycle
+
+static bool fastPWM;
+
 //2 second filter (ADC is PID_TIM_HZ Hz)
 history<uint16_t, PID_TIM_HZ> rawTempFilter = { { 0 }, 0, 0 };
 void resetWatchdog() {
@@ -190,6 +198,41 @@ void setTipPWM(uint8_t pulse) {
 	pendingPWM = pulse;
 }
 
+static void switchToFastPWM(void) {
+	fastPWM = true;
+	totalPWM = powerPWM + tempMeasureTicks * 2;
+	htim2.Instance->ARR = totalPWM;
+	// ~3.5 Hz rate
+	htim2.Instance->CCR1 = powerPWM + holdoffTicks * 2;
+	// 2 MHz timer clock/2000 = 1 kHz tick rate
+	htim2.Instance->PSC = 2000;
+}
+
+static void switchToSlowPWM(void) {
+	fastPWM = false;
+	totalPWM = powerPWM + tempMeasureTicks;
+	htim2.Instance->ARR = totalPWM;
+	// ~1.84 Hz rate
+	htim2.Instance->CCR1 = powerPWM + holdoffTicks;
+	// 2 MHz timer clock/4000 = 500 Hz tick rate
+	htim2.Instance->PSC = 4000;
+}
+
+bool tryBetterPWM(uint8_t pwm) {
+	if (fastPWM && pwm == powerPWM) {
+		// maximum power for fast PWM reached, need to go slower to get more
+		switchToSlowPWM();
+		return true;
+	} else if (!fastPWM && pwm < 230) {
+		// 254 in fast PWM mode gives the same power as 239 in slow
+		// allow for some reasonable hysteresis by switching only when it goes
+		// below 230 (equivalent to 245 in fast mode)
+		switchToFastPWM();
+		return true;
+	}
+	return false;
+}
+
 // These are called by the HAL after the corresponding events from the system
 // timers.
 
@@ -299,6 +342,10 @@ uint8_t getButtonB() {
 			1 : 0;
 }
 
+void BSPInit(void) {
+	switchToFastPWM();
+}
+
 void reboot() {
 
 	NVIC_SystemReset();

workspace/TS100/Core/BSP/Miniware/Setup.c

@@ -315,13 +315,15 @@ static void MX_TIM2_Init(void) {
 	// Timer 2 is fairly slow as its being used to run the PWM and trigger the ADC
 	// in the PWM off time.
 	htim2.Instance = TIM2;
-	htim2.Init.Prescaler = 4000; //1mhz tick rate/800 = 1.25 KHz tick rate
+	// dummy value, will be reconfigured by BSPInit()
+	htim2.Init.Prescaler = 2000; // 2 MHz timer clock/2000 = 1 kHz tick rate
 
 	// pwm out is 10k from tim3, we want to run our PWM at around 10hz or slower on the output stage
-	// These values give a rate of around 8Hz
+	// These values give a rate of around 3.5 Hz for "fast" mode and 1.84 Hz for "slow"
 	htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
-	htim2.Init.Period = 255 + 17;
-	htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV4;  // 4mhz before divide
+	// dummy value, will be reconfigured by BSPInit()
+	htim2.Init.Period = 255 + 17 * 2;
+	htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV4;  // 8 MHz (x2 APB1) before divide
 	htim2.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
 	htim2.Init.RepetitionCounter = 0;
 	HAL_TIM_Base_Init(&htim2);
@@ -337,7 +339,8 @@ static void MX_TIM2_Init(void) {
 	HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig);
 
 	sConfigOC.OCMode = TIM_OCMODE_PWM1;
-	sConfigOC.Pulse = 255 + 13;  //13 -> Delay of 5ms
+	// dummy value, will be reconfigured by BSPInit()
+	sConfigOC.Pulse = 255 + 13 * 2;  // 13 -> Delay of 7 ms
 	//255 is the largest time period of the drive signal, and then offset ADC sample to be a bit delayed after this
 	/*
 	 * It takes 4 milliseconds for output to be stable after PWM turns off.

workspace/TS100/Core/BSP/Miniware/preRTOS.cpp

@@ -17,6 +17,7 @@ void preRToSInit() {
 	 */
 	HAL_Init();
 	Setup_HAL();  // Setup all the HAL objects
+	BSPInit();
 #ifdef I2C_SOFT
 	I2CBB::init();
 #endif

workspace/TS100/Core/Inc/power.hpp

@@ -25,6 +25,4 @@ extern expMovingAverage<uint32_t, wattHistoryFilter> x10WattHistory;
 int32_t tempToX10Watts(int32_t rawTemp);
 void setTipX10Watts(int32_t mw);
 uint8_t X10WattsToPWM(int32_t milliWatts, uint8_t sample = 0);
-int32_t PWMToX10Watts(uint8_t pwm, uint8_t sample = 0);
-uint32_t availableW10(uint8_t sample) ;
 #endif /* POWER_HPP_ */

workspace/TS100/Core/Src/power.cpp

@@ -9,8 +9,7 @@
 #include <Settings.h>
 #include <BSP.h>
 
-const uint16_t powerPWM = 255;
-const uint16_t totalPWM = 255 + 17; //htim2.Init.Period, the full PWM cycle
+static int32_t PWMToX10Watts(uint8_t pwm, uint8_t sample);
 
 expMovingAverage<uint32_t, wattHistoryFilter> x10WattHistory = { 0 };
 
@@ -30,7 +29,7 @@ void setTipX10Watts(int32_t mw) {
 	x10WattHistory.update(actualMilliWatts);
 }
 
-uint32_t availableW10(uint8_t sample) {
+static uint32_t availableW10(uint8_t sample) {
 	//P = V^2 / R, v*v = v^2 * 100
 	//				R = R*10
 	// P therefore is in V^2*100/R*10 = W*10.
@@ -56,15 +55,22 @@ uint8_t X10WattsToPWM(int32_t milliWatts, uint8_t sample) {
 	}
 	//	if (milliWatts > (int(systemSettings.pidPowerLimit) * 10))
 //		milliWatts = (int(systemSettings.pidPowerLimit) * 10);
+
 	//Calculate desired milliwatts as a percentage of availableW10
-	uint32_t pwm = (powerPWM * milliWatts) / availableW10(sample);
-	if (pwm > powerPWM) {
-		pwm = powerPWM;	//constrain to max PWM counter, shouldnt be possible, but small cost for safety to avoid wraps
-	}
+	uint32_t pwm;
+	do {
+		pwm = (powerPWM * milliWatts) / availableW10(sample);
+		if (pwm > powerPWM) {
+			// constrain to max PWM counter, shouldn't be possible,
+			// but small cost for safety to avoid wraps
+			pwm = powerPWM;
+		}
+	} while (tryBetterPWM(pwm));
+
 	return pwm;
 }
 
-int32_t PWMToX10Watts(uint8_t pwm, uint8_t sample) {
+static int32_t PWMToX10Watts(uint8_t pwm, uint8_t sample) {
 	uint32_t maxMW = availableW10(sample); //Get the milliwatts for the max pwm period
 	//Then convert pwm into percentage of powerPWM to get the percentage of the max mw
 	return (((uint32_t) pwm) * maxMW) / powerPWM;

workspace/TS100/configuration.h

@@ -131,7 +131,7 @@
 
 #ifdef MODEL_TS100
 const int32_t tipMass = 45; // X10 watts to raise 1 deg C in 1 second
-const uint8_t tipResistance = 85; //x10 ohms, 8.5 typical for ts100, 4.5 typical for ts80
+const uint8_t tipResistance = 75; //x10 ohms, 7.5 typical for ts100 tips
 #endif
 
 #ifdef MODEL_TS80