Use PWM to slowly lower pen

stm32f103c8t6/build_number.txt

@@ -1 +1 @@
-282
+319

stm32f103c8t6/src/pinning.h

@@ -8,7 +8,7 @@
 // #define PIN_USB_PULLUP          15  // PA15 - 1.5 kΩ to D+
 
 // Port B
-#define PIN_PEN_STATE           6   // PB6
+#define PIN_PEN_STATE           6   // PB6  - TIM4_CH1
 
 // Port C
 #define PIN_LED                 13  // PC13 - Status LED

stm32f103c8t6/src/pwm_output.c

@@ -9,11 +9,13 @@ MODULE_OWNS_PIN(GPIOA, PIN_OUTPUT_X);
 MODULE_OWNS_PIN(GPIOA, PIN_OUTPUT_Y);
 MODULE_OWNS_PIN(GPIOB, PIN_PEN_STATE);
 MODULE_OWNS_PERIPHERAL(TIM1);
+MODULE_OWNS_PERIPHERAL(TIM4);
 
 static HPGL_Movement_t Output_Buffer[CONFIG_BUFFER_MOVEMENTS];
 static const HPGL_Movement_t *Output_BufferRead = Output_Buffer;
 static HPGL_Movement_t *Output_BufferWrite = Output_Buffer;
-static bool Output_PenIsDown;
+//static bool Output_PenIsDown;
+static unsigned int Output_PenState = OUTPUT_PEN_UP;
 static unsigned int Output_DelayCounter = 0;
 
 typedef struct
@@ -26,7 +28,7 @@ static Output_Coordinate_t Output_CurrentLineStart = {0, 0};
 static Output_Coordinate_t Output_CurrentLineEnd = {0, 0};
 static unsigned int Output_CurrentLineLength;
 static unsigned int Output_CurrentLinePosition;
-static unsigned int Output_CurrentVelocity = OUTPUT_LENGTH_SCALE / 2;
+static unsigned int Output_CurrentVelocity = OUTPUT_LENGTH_SCALE / 3;
 
 bool Output_EnqueueMovement(HPGL_Movement_t movement)
 {
@@ -60,14 +62,14 @@ bool Output_EnqueueMovement(HPGL_Movement_t movement)
 
 static void Output_PenDown(void)
 {
-    GPIOB->BRR = (1 << PIN_PEN_STATE);
-    Output_PenIsDown = true;
+    Output_PenState = OUTPUT_PEN_START;
+    TIM4->CCR1 = Output_PenState;
 }
 
 static void Output_PenUp(void)
 {
-    GPIOB->BSRR = (1 << PIN_PEN_STATE);
-    Output_PenIsDown = false;
+    Output_PenState = OUTPUT_PEN_UP;
+    TIM4->CCR1 = Output_PenState;
 }
 
 static unsigned int Output_ApproximateLength(int dx, int dy)
@@ -100,17 +102,18 @@ static bool Output_FetchNextPoint(void)
     }
 
     const HPGL_Movement_t *movement = Output_BufferRead;
-    if(movement->pen_down != Output_PenIsDown)
+    if(movement->pen_down != (Output_PenState == OUTPUT_PEN_DOWN))
     {
         if(movement->pen_down)
         {
             Output_PenDown();
+            Output_DelayCounter = OUTPUT_PEN_DOWN_DELAY;
         }
         else
         {
             Output_PenUp();
+            Output_DelayCounter = OUTPUT_PEN_UP_DELAY;
         }
-        Output_DelayCounter = OUTPUT_PEN_DELAY;
         return false;
     }
 
@@ -139,8 +142,38 @@ static void Output_Position(Output_Coordinate_t position)
     TIM1->CCR2 = compare_y;
 }
 
+// Update the pen PWM output if the pen is currently moving, return false
+// otherwise
+static bool Output_UpdatePen(void)
+{
+    // Only the downwards motion of the pen is smoothed. Thus, the direction is
+    // implied within the state variable (intermediate values only occur while
+    // the pen is being lowered).
+    if((Output_PenState == OUTPUT_PEN_DOWN)
+        || (Output_PenState == OUTPUT_PEN_UP))
+    {
+        return false;
+    }
+
+    Output_PenState += OUTPUT_PEN_STEP;
+    if(Output_PenState >= OUTPUT_PEN_STOP)
+    {
+        Output_PenState = OUTPUT_PEN_DOWN;
+    }
+    TIM4->CCR1 = Output_PenState;
+
+    return true;
+}
+
 void Output_Tick(void)
 {
+    // Do not move while pen is lowered
+    if(Output_UpdatePen())
+    {
+        return;
+    }
+
+    // Wait for a bit longer after each pen state change
     if(Output_DelayCounter > 0)
     {
         Output_DelayCounter--;
@@ -188,6 +221,7 @@ void Output_Tick(void)
 void Output_Init(void)
 {
     RCC->APB2ENR |= RCC_APB2ENR_TIM1EN;
+    RCC->APB1ENR |= RCC_APB1ENR_TIM4EN;
     RCC->APB2ENR |= RCC_APB2ENR_IOPAEN;
     RCC->APB2ENR |= RCC_APB2ENR_IOPBEN;
 
@@ -202,7 +236,7 @@ void Output_Init(void)
 
     GPIOB->CRL = (GPIOB->CRL
         & ~(0xf << (4 * PIN_PEN_STATE)))
-        | (0x6 << (4 * PIN_PEN_STATE)) // OD output, 2 MHz
+        | (0xe << (4 * PIN_PEN_STATE))      // AF-OD output, 2 MHz
         ;
 
     TIM1->CCMR1 = TIM_CCMR1_OC1PE | TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1
@@ -213,6 +247,13 @@ void Output_Init(void)
     TIM1->DIER = TIM_DIER_UIE;
     TIM1->CR1 = TIM_CR1_CEN;
     NVIC_EnableIRQ(TIM1_UP_IRQn);
+
+    TIM4->CCMR1 = TIM_CCMR1_OC1PE | TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1;
+    TIM4->CCER = TIM_CCER_CC1P | TIM_CCER_CC1E;
+    TIM4->PSC = OUTPUT_PEN_PRESCALER - 1;
+    TIM4->ARR = OUTPUT_PEN_RELOAD;
+    TIM4->CCR1 = OUTPUT_PEN_UP;
+    TIM4->CR1 = TIM_CR1_CEN;
 }
 
 void TIM1_UP_IRQHandler(void)

stm32f103c8t6/src/pwm_output.h

@@ -1,8 +1,10 @@
 #pragma once
 
 #include "hpgl.h"
+#include "clock.h"
 
-// PWM coordinate output settings
+// PWM coordinate output settings (reoslution also determines the movement
+// timer tick frequency)
 #define OUTPUT_PWM_RESOLUTION   15  // In bits
 #define OUTPUT_PWM_OFFSET       300 // Minimum value
 
@@ -16,7 +18,24 @@
 #define OUTPUT_LENGTH_SCALE     (1 << 3)
 
 // Delay after initiating pen-up/-down before continuing movements
-#define OUTPUT_PEN_DELAY        200 // In timer ticks
+#define OUTPUT_PEN_UP_DELAY     200 // In movement timer ticks
+#define OUTPUT_PEN_DOWN_DELAY   20  // In movement timer ticks
+
+// PWM frequency for the pen state output
+#define OUTPUT_PEN_FREQUENCY    120 // In Hertz
+
+// Resulting timer settings for pen PWM output
+#define OUTPUT_PEN_PRESCALER    (CLOCK_APB1 / OUTPUT_PEN_FREQUENCY / 65535 + 1)
+#define OUTPUT_PEN_RELOAD       ((uint16_t)(CLOCK_APB1 / OUTPUT_PEN_FREQUENCY \
+                                / OUTPUT_PEN_PRESCALER - 1))
+#define OUTPUT_PEN_UP           0
+#define OUTPUT_PEN_DOWN         (OUTPUT_PEN_RELOAD + 1)
+
+// Start and stop duty cycles and duty cycle step (per movement timer tick) for
+// gracefully lowering the pen
+#define OUTPUT_PEN_START        ((unsigned int)(0.4 * OUTPUT_PEN_RELOAD))
+#define OUTPUT_PEN_STOP         ((unsigned int)(0.43 * OUTPUT_PEN_RELOAD))
+#define OUTPUT_PEN_STEP         ((unsigned int)(0.0001 * OUTPUT_PEN_RELOAD))
 
 void Output_Init(void);
 bool Output_EnqueueMovement(HPGL_Movement_t movement);