84. Structures-iii

Question.3

A developer defines a memory-mapped peripheral struct:

typedef struct {
   volatile uint32_t CTRL;
   volatile float THRESHOLD;
   volatile uint32_t STATUS;
} ADC_Periph;

#define ADC1 ((ADC_Periph *)0x40012000)
ADC1->THRESHOLD = 2.5f;

What is problematic about this struct?

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Nothing — float is 4 bytes like uint32_t, so alignment is fine
Hardware registers are integer-addressed — writing a float to a register address writes the float's IEEE 754 bit pattern, not the numeric value 2.5
Float cannot be volatile
The struct size would be wrong due to float alignment