cmsis_os.h中定义的:
typedef struct {
osStatus status; ///< status code: event or error information
union {
uint32_t v; ///< message as 32-bit value
void *p; ///< message or mail as void pointer
int32_t signals; ///< signal flags
} value; ///< event value
union {
osMailQId mail_id; ///< mail id obtained by \ref osMailCreate
osMessageQId message_id; ///< message id obtained by \ref osMessageCreate
} def; ///< event definition
} osEvent;