need help on understanding RMT item

[manoj15]

Code: Select all

typedef struct rmt_item32_s {
    union {
        struct {
            uint32_t duration0 :15;
            uint32_t level0 :1;
            uint32_t duration1 :15;
            uint32_t level1 :1;
        };
        uint32_t val;
    };
} rmt_item32_t;

I want to understand why the structure was packed over union ?
and how is the packing happening ? based on the datasheet I understand that each item is only 32 bit only consist of level and pulse length while the struct member each @ 32bit length.

[ESP_Angus]

That's right, each item register is only 32 bits wide.

The union is between "val", which gives thar raw 32-bit value of the item register and the anoymous struct, which uses a C feature called "bitfields" to have integers which are only X bits wide. The width of each field is given after the ":" on the line. This means the total width of the struct is also 32 bits (15+1+15+1).

This provides an easy way to access the level and duration of each item via struct fields, without needing to manually mask and shift each field.