simple_source模塊的功能是按照配置產生包，包括不同的包格式和產生速率，也是比較簡單的進程模型。

參考了《 opnet process model：simple_source分析 》 http://hi.baidu.com/ebinghaus/blog/item/c7cade9228876c83a877a405.html

　　該模塊有4個local statistic，注意有5個model attribute，分別是Packet Interarrival Time，Packet Size，Packet Format，Start Time，Stop Time，這些是在使用該模塊時需要配置的，當然也可以使用默認配置。

狀態機也很簡單：

在header block中定義了

/* Include files.?????*/
#include?<oms_dist_support.h>　　 //注意該模塊使用了外部文件《oms_dist_support》和《oms_string_support》

/* Special attribute values.??*/
#define??SSC_INFINITE_TIME??-1.0　　　　 //定義無窮大時間為-1

/* Interrupt code values.???*/　　 //注意這里的中斷代碼是自定義的，為了在產生自中斷是使用
#define??SSC_START????0
#define??SSC_GENERATE???1
#define??SSC_STOP????2

/* Node configuration constants.?*/
#define??SSC_STRM_TO_LOW???0　　　　 //發送的stream index，默認的，該模塊只有一個stream連接，所以不需要動態獲取stream index

/* Macro definitions for state??transitions.*/　　　 //轉換條件為中斷代碼是自定義的常量：

#define??START????(intrpt_code == SSC_START)
#define??DISABLED???(intrpt_code == SSC_STOP)
#define??STOP????(intrpt_code == SSC_STOP)
#define??PACKET_GENERATE??(intrpt_code == SSC_GENERATE)

/* Function prototypes.????*/
static void???ss_packet_generate (void);　　 //產生包的函數，在function block中定義

?

一，INIT的入口代碼：

/* At this initial state, we read the values of source attributes?*/
/* and schedule a selt interrupt that will indicate our start time?*/
/* for packet generation.???????????*/

/* Obtain the object id of the surrounding module.?????*/
own_id = op_id_self ();　　　　　　　　 //首先得到surrounding objid，應該是自己的objid，后面根據objid獲取對象的屬性

/* Read the values of the packet generation parameters, i.e. the?*/
/* attribute values of the surrounding module.??????*/

//用op_ima_obj_attr_get()得到對象的屬性的值，是產生包的參數。注意interarrival_str和size_str是臨時變量，還是char數組類型。
op_ima_obj_attr_get (own_id, "Packet Interarrival Time", interarrival_str);
op_ima_obj_attr_get (own_id, "Packet Size",????????????? size_str);
op_ima_obj_attr_get (own_id, "Packet Format",??????????? format_str);
op_ima_obj_attr_get (own_id, "Start Time",?????????????? &start_time);
op_ima_obj_attr_get (own_id, "Stop Time",??????????????? &stop_time);

/* Load the PDFs that will be used in computing the packet???*/
/* interarrival times and packet sizes.????????*/

//裝入PDF，用于前兩個參數，得到包產生和包大小的分布，函數是oms_dist_load_from_string()，這樣很方便的使用string類型的參數。
//獲得的是分布函數的句柄，注意兩個句柄都是state variable，類型為Omst_dist_handle。

interarrival_dist_ptr = oms_dist_load_from_string (interarrival_str);
pksize_dist_ptr?????? = oms_dist_load_from_string (size_str);

/* Verify the existence of the packet format to be used for???generated packets.?*/
if (strcmp (format_str, "NONE") == 0)　　 //檢查是否是無格式包
?{
?/* We will generate unformatted packets. Set the flag.???*/
?generate_unformatted = OPC_TRUE;
?}
else
?{
?/* We will generate formatted packets. Turn off the flag.??*/
?generate_unformatted = OPC_FALSE;　　 //不是無格式包

?/* Get the list of all available packet formats.????*/

//用prg_tfile_name_list_get()得到所有可用的包格式
?pk_format_names_lptr = prg_tfile_name_list_get (PrgC_Tfile_Type_Packet_Format);

?/* Search the list for the requested packet format.????*/
?format_found = OPC_FALSE;
?for (i = prg_list_size (pk_format_names_lptr); ((format_found == OPC_FALSE) && (i > 0)); i--)
??{
??/* Access the next format name and compare with requested format name?*/
??found_format_str = (char *) prg_list_access (pk_format_names_lptr, i - 1);
??if (strcmp (found_format_str, format_str) == 0)
???format_found = OPC_TRUE;　　 //找到了需求的包格式
??}

??? if (format_found == OPC_FALSE)
??{
??/* The requested format does not exist. Generate unformatted packets.?????*/
??generate_unformatted = OPC_TRUE;
?
??/* Display an appropriate warning.???????*/
??op_prg_odb_print_major ("Warning from simple packet generator model (simple_source):",
????????"The specified packet format", format_str,
????????"is not found. Generating unformatted packets instead.", OPC_NIL);
??}

?/* Destroy the lits and its elements since we don't need it??*/
?/* anymore.??????????????*/
?prg_list_free (pk_format_names_lptr);
?prg_mem_free? (pk_format_names_lptr);
?}?
?
/* Make sure we have valid start and stop times, i.e. stop time is??not earlier than start time.?*/
if ((stop_time <= start_time) && (stop_time != SSC_INFINITE_TIME))　　 //開始/結束時間不合法，設置開始仿真時間為無窮大
?{
?/* Stop time is earlier than start time. Disable the source.?*/
?start_time = SSC_INFINITE_TIME;

?/* Display an appropriate warning.????????*/
?op_prg_odb_print_major ("Warning from simple packet generator model (simple_source):",
???????"Although the generator is not disabled (start time is set to a finite value),",
???????"a stop time that is not later than the start time is specified.",
???????"Disabling the generator.", OPC_NIL);
?}

/* Schedule a self interrupt that will indicate our start time for?*/
/* packet generation activities. If the source is disabled,???*/
/* schedule it at current time with the appropriate code value.??*/

//產生自中斷，以指示開始產生包的時間， 如果停止產生包時刻小于開始產生包的時刻（這時開始產生包的時間是無限大）在當前仿真時刻產生中斷號為SSC_STOP中斷
if (start_time == SSC_INFINITE_TIME)
?{
?op_intrpt_schedule_self (op_sim_time (), SSC_STOP);　　 //馬上給出自中斷
?}
else
?{
?op_intrpt_schedule_self (start_time, SSC_START);　　　 //自中斷，在開始時間，中斷號為SSC_START

?/* In this case, also schedule the interrupt when we will stop?*/
?/* generating packets, unless we are configured to run until?*/
?/* the end of the simulation.?????????*/
?if (stop_time != SSC_INFINITE_TIME)
??{
??op_intrpt_schedule_self (stop_time, SSC_STOP);　　 //當結束時間不是無限大時，在結束時間產生自中斷，中斷號為SSC_STOP
??}
?
?next_intarr_time = oms_dist_outcome (interarrival_dist_ptr);　　 //通過分布函數句柄計算產生下一個包的時間間隔，這里是state variable

?/* Make sure that interarrival time is not negative. In that case it will be set to 0.*/
?if (next_intarr_time <0)
??{
??next_intarr_time = 0.0;　　 //保證間隔時間不小于0
??}

?}

/* Register the statistics that will be maintained by this model.?*/

//注冊局部統計量，返回局部統計量的句柄
bits_sent_hndl???? ?= op_stat_reg ("Generator.Traffic Sent (bits/sec)",???OPC_STAT_INDEX_NONE, OPC_STAT_LOCAL);
packets_sent_hndl?? = op_stat_reg ("Generator.Traffic Sent (packets/sec)",??OPC_STAT_INDEX_NONE, OPC_STAT_LOCAL);
packet_size_hndl??? = op_stat_reg ("Generator.Packet Size (bits)",????????????? OPC_STAT_INDEX_NONE, OPC_STAT_LOCAL);
interarrivals_hndl? = op_stat_reg ("Generator.Packet Interarrival Time (secs)", OPC_STAT_INDEX_NONE, OPC_STAT_LOCAL);

?

二， 由于初始狀態是非強制狀態，進程執行完入口代碼后，停留在該狀態等待中斷觸發轉移狀態,仿真時刻到10s（屬性start_time設置的值）時將產生中斷號為SSC_START中斷，中斷產生后將首先執行當前狀態的出口代碼，初始狀態的出口代碼如下：
intrpt_code = op_intrpt_code ();　　 //得到當前的中斷代碼

這時條件START滿足， 進程將從初始狀態轉換到generate狀態 ，轉移時首先執行轉移函數ss_packet_generate (void)，在function block中定義的轉移函數如下：

?

static void ss_packet_generate (void)
?{
?Packet*????pkptr;
?double????pksize;

?

?/** This function creates a packet based on the packet generation??**/
?/** specifications of the source model and sends it to the lower layer.?**/
?FIN (ss_packet_generate ());

?

?/* Generate a packet size outcome.?????*/
?pksize = (double) ceil (oms_dist_outcome (pksize_dist_ptr));　　 //通過分布函數句柄得到包大小，再通過ceil()函數向上舍入，得到包大小
?
?/* Create a packet of specified format and size.?*/
?if (generate_unformatted == OPC_TRUE)
??{
??/* We produce unformatted packets. Create one.?*/
??pkptr = op_pk_create (pksize);　　　　　　　　　　　　 //使用op_pk_creat()函數產生無格式包
??}
?else
??{
??/* Create a packet with the specified format.?*/
??pkptr = op_pk_create_fmt (format_str);　　　　　　 //使用op_pk_creat_fmt()函數產生有格式包
??op_pk_total_size_set (pkptr, pksize);　　　　　　　　 //置有格式包的總大小
??}

?

?/* Update the packet generation statistics.???*/　　 //通過局部統計量句柄更新統計量，注意xxx/sec的量都是在更新后馬上清零
?op_stat_write (packets_sent_hndl, 1.0);
?op_stat_write (packets_sent_hndl, 0.0);
?op_stat_write (bits_sent_hndl, (double) pksize);
?op_stat_write (bits_sent_hndl, 0.0);
?op_stat_write (packet_size_hndl, (double) pksize);
?op_stat_write (interarrivals_hndl, next_intarr_time);

?

?/* Send the packet via the stream to the lower layer.?*/
?op_pk_send (pkptr, SSC_STRM_TO_LOW);　　　　 //發送包到定義好的stream index，默認為0

?

?FOUT;
?}?

?

三， ? 執行完轉移函數后將跳到generate狀態，并首先執行入口代碼，如下：

/* At the enter execs of the "generate" state we schedule the??*/
/* arrival of the next packet.??????????*/
next_intarr_time = oms_dist_outcome (interarrival_dist_ptr);　　 //通過分布函數句柄得到下一個包的產生時間間隔

?

/* Make sure that interarrival time is not negative. In that case it will be set to 0.*/
if (next_intarr_time <0)
?{
?next_intarr_time = 0;
?}

//在當前時間+間隔時間后，產生自中斷，中斷號為SSC_GENERATE，注意返回值為Evhandle類型

next_pk_evh?= op_intrpt_schedule_self (op_sim_time () + next_intarr_time, SSC_GENERATE);

?

四， 執行完入口代碼后，進程將停留在generate狀態等待中斷，當下一個中斷發生，進行狀態轉換，首先執行generate狀態的出口代碼：

intrpt_code = op_intrpt_code ();　　//得到中斷號

然后判斷轉移條件。

如果是STOP，執行stop狀態的入口代碼：

/* When we enter into the "stop" state, it is the time for us to?*/
/* stop generating traffic. We simply cancel the generation of the?*/
/* next packet and go into a silent mode by not scheduling anything?*/
/* else.???????????????*/
if (op_ev_valid (next_pk_evh) == OPC_TRUE)　　　　 //如果下一個事件仍然有效，就取消該事件，使用事件句柄
?{
?op_ev_cancel (next_pk_evh);
?}

OPNET學習筆記之simple_source模塊