add untested driver prototype for DHT11 humidity and temperature sensor

Core/Inc/dht11.h

@@ -0,0 +1,30 @@
+#ifndef __DHT11
+#define __DHT11
+
+#define SKIP_LOW while (!(GPIOD->IDR & 0x0800)) {}
+#define SKIP_HIGH while (GPIOD->IDR & 0x0800) {}
+
+#define FILL_REGISTER do { \
+	for (int i = 0; i < 8; i++) { \
+		read_register <<= 1; \
+		SKIP_LOW; \
+		read_register |= dht11_measure_high_duration(); \
+	} } while (0)
+
+struct SysTickConfig {
+	uint32_t ctrl;
+	uint32_t load;
+	uint32_t val;
+};
+
+struct DHT11_Data {
+	uint8_t humid_integral;
+	uint8_t humid_decimal;
+	uint8_t temp_integral;
+	uint8_t temp_decimal;
+	uint8_t crc;
+};
+
+void dht11_show_both(void);
+
+#endif

Core/Src/dht11.c

@@ -0,0 +1,98 @@
+#include "main.h"
+#include "generic_macros.h"
+#include "dht11.h"
+
+static struct SysTickConfig stc;
+static uint32_t *systick_base = (uint32_t *) SysTick_BASE;
+
+static void wait(uint32_t wait_us)
+{
+	int target_time = *(systick_base+8);
+	target_time -= wait_us << 4;
+
+	while (*(systick_base+8) > target_time) {}
+}
+
+static void dht11_save_systick_state(void)
+{
+	stc.ctrl = *(systick_base + 0);
+	stc.load = *(systick_base + 4);
+	stc.val  = *(systick_base + 8);
+}
+
+static void dht11_load_systick_state(void)
+{
+	*(systick_base + 4) = stc.load;
+	*(systick_base + 8) = stc.val;
+	*(systick_base + 0) = stc.ctrl;
+}
+
+static void dht11_init_systick(void)
+{
+	dht11_save_systick_state();
+
+	*(systick_base + 0) = 0x5;      // disable /8 prescaler, no interrupts, enable counting
+	*(systick_base + 4) = 0xFFFFFF; // load largest possible value
+
+	// verify value load
+	if (*(systick_base + 8) == 0)
+		PANIC(0x4000);
+}
+
+static size_t dht11_measure_high_duration(void)
+{
+	int current_time = *(systick_base+8);
+	SKIP_HIGH;
+
+	// elapsed_time > 49us ? 1 : 0
+	return (current_time - *(systick_base+8)) > (49 << 4);
+}
+
+static void dht11_read_value(struct DHT11_Data *data)
+{
+	dht11_init_systick();
+
+	register uint8_t read_register = 0;
+
+	GPIOD->BSRR = GPIO_PIN_11;       // enable DHT11
+	wait(50000);                     // hold HIGH for 50 ms
+	GPIOD->BSRR = GPIO_PIN_11 << 16; // start signal
+	wait(30000);                     // hold it for 30 ms
+	GPIOD->BSRR = GPIO_PIN_11;       // pull up, DHT will now take control over the connection
+
+	// switch GPIOD 11 to input mode
+	GPIOD->MODER &= 0xFF3FFFFF;
+
+	// read transmission start sequence from DHT11
+	SKIP_HIGH;
+	SKIP_LOW;
+	SKIP_HIGH;
+
+	// read humidity integral
+	FILL_REGISTER;
+	data->humid_integral = read_register;
+
+	// read humidity decimal
+	FILL_REGISTER;
+	data->humid_decimal = read_register;
+
+	// read temperature integral
+	FILL_REGISTER;
+	data->temp_integral = read_register;
+
+	// read temperature decimal
+	FILL_REGISTER;
+	data->temp_decimal = read_register;
+
+	// read crc
+	FILL_REGISTER;
+	data->crc = read_register;
+
+	dht11_load_systick_state();
+}
+
+void dht11_show_both(void)
+{
+	struct DHT11_Data data;
+	dht11_read_value(&data);
+}

Core/Src/main.c

@@ -25,6 +25,7 @@
 #include "generic_macros.h"
 #include "lcd.h"
 #include "external_temp.h"
+#include "dht11.h"
 
 /* USER CODE END Includes */
 
@@ -49,6 +50,7 @@ ADC_HandleTypeDef hadc1;
 /* USER CODE BEGIN PV */
 
 void ((*executors[])(void)) = {
+		dht11_show_both,
 		external_temp_show_celsius,
 		external_temp_show_fahrenheit
 };
@@ -104,6 +106,7 @@ int main(void)
 
   GPIOD->ODR = 0xF000;
   display_init();
+  HAL_Delay(1000);
   GPIOD->ODR = 0x0000;
 
   /* USER CODE END 2 */
@@ -236,7 +239,8 @@ static void MX_GPIO_Init(void)
                           |GPIO_PIN_13|GPIO_PIN_14|GPIO_PIN_15, GPIO_PIN_RESET);
 
   /*Configure GPIO pin Output Level */
-  HAL_GPIO_WritePin(GPIOD, GPIO_PIN_12|GPIO_PIN_13|GPIO_PIN_14|GPIO_PIN_15, GPIO_PIN_RESET);
+  HAL_GPIO_WritePin(GPIOD, GPIO_PIN_11|GPIO_PIN_12|GPIO_PIN_13|GPIO_PIN_14
+                          |GPIO_PIN_15, GPIO_PIN_RESET);
 
   /*Configure GPIO pin : PA0 */
   GPIO_InitStruct.Pin = GPIO_PIN_0;
@@ -253,8 +257,10 @@ static void MX_GPIO_Init(void)
   GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
   HAL_GPIO_Init(GPIOE, &GPIO_InitStruct);
 
-  /*Configure GPIO pins : PD12 PD13 PD14 PD15 */
-  GPIO_InitStruct.Pin = GPIO_PIN_12|GPIO_PIN_13|GPIO_PIN_14|GPIO_PIN_15;
+  /*Configure GPIO pins : PD11 PD12 PD13 PD14
+                           PD15 */
+  GPIO_InitStruct.Pin = GPIO_PIN_11|GPIO_PIN_12|GPIO_PIN_13|GPIO_PIN_14
+                          |GPIO_PIN_15;
   GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
   GPIO_InitStruct.Pull = GPIO_NOPULL;
   GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;