The propose of 2 uploadInfos in external mode?

In external mode, BdUploadInfo data structure describes the data that need to be upload to the host(Simulink).

/*
* The BdUploadInfo contains all information regarding data logging.
*/
struct BdUploadInfo_tag {
int32_T        upInfoIdx;  /* index of upInfo in the array                 */
int32_T        nSys;       /* # of sys's for which data logging is active  */
SysUploadTable *sysTables; /* array of SysUploadTables                     */
CircularBuf    *circBufs;  /* circular buffers to store upload data        */
BufMemList     bufMemList; /* list of buffer memory holding data to upload */
TriggerInfo  trigInfo;
};

My question is why there are 2 uploadInfos (type BdUploadInfo) in updown.c, as follow:

#define NUM_UPINFOS   2
static  BdUploadInfo  uploadInfoArray[NUM_UPINFOS];

It seems simulink use these two uploadinfos, and when the host(Simulink) connects to the target, its dignostic viewer outputs some external mode's information, as follow. Note that the host(Simulink) alsoe send cancel logging command (EXT_CANCEL_LOGGING_RESPONSE) to the target for uploadIdx 1 as well.

action: EXT_SELECT_SIGNALS
action: EXT_CANCEL_LOGGING
Got EXT_SETPARAM_RESPONSE from target with status OK.
Got EXT_SELECT_SIGNALS_RESPONSE from target for upInfoIdx 0 with status OK.
action: EXT_SELECT_TRIGGER
Got EXT_CANCEL_LOGGING_RESPONSE from target for upInfoIdx 1 with status OK.
Got EXT_SELECT_TRIGGER_RESPONSE from target for upInfoIdx 0 with status OK.
action: EXT_ARM_TRIGGER
Got EXT_ARM_TRIGGER_RESPONSE from target for upInfoIdx 0 with status OK.
action: EXT_MODEL_START
Got EXT_MODEL_START_RESPONSE packet from target.
action: EXT_MODEL_STOP
Got EXT_MODEL_SHUTDOWN packet from target.
action: EXT_DISCONNECT_CONFIRMED