前36字节（[0-35）的数据结构：
typedef struct
{
bus_common_header_t common; // 20字节 [0~19]
cdc_header_t cdc_header; // 16字节 [20~35]
} control_header_t; // 36字节
typedef struct
{
whd_buffer_header_t buffer_header; // 8字节 [0~7]（CMD53不发送此数据）
uint8_t bus_header[BUS_HEADER_LEN]; // 12字节 (sdpcm_header_t) [8~19]
} bus_common_header_t;
typedef struct
{
whd_buffer_queue_ptr_t queue_next; // 4字节 (struct pbuf *) [0~3]（CMD53不发送此数据）
char bus_header[MAX_BUS_HEADER_SIZE]; // 4字节 (whd_transfer_bytes_packet_t::bus_header) [4~7]（CMD53不发送此数据）
} whd_buffer_header_t;
typedef struct
{
uint8_t bus_header[MAX_BUS_HEADER_SIZE]; // [4-7]
uint32_t data[1]; // [8-]
} whd_transfer_bytes_packet_t;
typedef struct
{
uint16_t frametag[2]; // 4字节 {size, ~size} [8~11]
sdpcm_sw_header_t sw_header; // 6+2=8字节 (channel_and_flags, header_length, sequence) [12~19]
} sdpcm_header_t; // 共12字节
typedef struct
{
uint8_t sequence; /* Rx/Tx sequence number */ // [12]
uint8_t channel_and_flags; /* 4 MSB Channel number, 4 LSB arbitrary flag */ // [13]
uint8_t next_length; /* Length of next data frame, reserved for Tx */ // [14]
uint8_t header_length; /* Data offset */ // [15]
uint8_t wireless_flow_control; /* Flow control bits, reserved for Tx */ // [16]
uint8_t bus_data_credit; /* Maximum Sequence number allowed by firmware for Tx */ // [17]
uint8_t _reserved[2]; /* Reserved */ // [18-19]
} sdpcm_sw_header_t;
typedef struct
{
uint32_t cmd; /* ioctl command value */ // [20~23]
uint32_t len; /* lower 16: output buflen; upper 16: input buflen (excludes header) */ // [24~27]
uint32_t flags; /* flag defns given in bcmcdc.h */ // [28~31]
uint32_t status; /* status code returned from the device */ // [32~35]
} cdc_header_t;
