expand and cleanup example

examples/struct_gpio/struct_gpio.c

@@ -17,7 +17,12 @@ int main()
 	// Enable GPIOs
 	RCC->APB2PCENR |= RCC_APB2Periph_GPIOD | RCC_APB2Periph_GPIOC;
 
-    // GPIO D0, D4 Push-Pull
+	Delay_Ms( 100 );
+
+	// all floating inputs before
+	printf("CFGLR: %lX\n", GPIOD->CFGLR); // -> CFGLR: 44444444
+
+    // GPIO D0, D4 Push-Pull, D1/SWIO floating, default analog input
 	GPIOD->CFGLR_bits = (struct CFGLR_t) {
 		.MODE0 = GPIO_CFGLR_MODE_OUT_10MHz,
 		.CNF0 = GPIO_CFGLR_CNF_OUT_PP,
@@ -27,31 +32,36 @@ int main()
 		.CNF4 = GPIO_CFGLR_CNF_OUT_PP,
 	};
 
-	// GPIO C0 Push-Pull
-	GPIOC->CFGLR_bits = (struct CFGLR_t) {
-		.MODE0 = GPIO_CFGLR_MODE_OUT_10MHz,
-		.CNF0  = GPIO_CFGLR_CNF_OUT_PP,
-	};
+	// all unconfigured pins are not 0b0000, aka analog inputs with TTL Schmitttrigger disabled
+	printf("CFGLR: %lX\n", GPIOD->CFGLR); // -> CFGLR: 10041
+
+	// GPIO C0 Push-Pull with 2 volatile writes
+	GPIOC->CFGLR_bits.MODE0 = GPIO_CFGLR_MODE_OUT_10MHz;
+	GPIOC->CFGLR_bits.CNF0  = GPIO_CFGLR_CNF_OUT_PP;
+
+	// read modify write
+	struct CFGLR_t ioc = GPIOC->CFGLR_bits;
+	ioc.MODE1 = GPIO_CFGLR_MODE_IN; // not volatile
+	ioc.CNF1 = GPIO_CNF_IN_ANALOG;  // not volatile
+	GPIOC->CFGLR_bits = ioc; // this should be one volatile write
 
 	while(1)
 	{
-		// Turn on GPIOs, set in BSHR
+		// Turn D0 on and D4 off at the same time
 		GPIOD->BSHR_bits = (struct BSHR_t) {
 			.BS0 = 1,
-			.BS4 = 1,
+			.BR4 = 1,
 		};
 		GPIOC->BSHR_bits.BS0 = 1;
-		printf( "+%lu\n", count++ );
 		Delay_Ms( 100 );
 
-		// Turn off GPIODs, clear in BSHR
+		// Turn D0 off and D4 on at the same time
 		GPIOD->BSHR_bits = (struct BSHR_t) {
 			.BR0 = 1,
-			.BR4 = 1,
+			.BS4 = 1,
 		};
 		// or clear in BCR
 		GPIOC->BCR_bits.BR0 = 1;
-		printf( "-%lu\n", count++ );
 		Delay_Ms( 100 );
 	}
 }