Asterisk Dial到 dahdi 驅動調用過程

Dail 是Asterisk 的一個application, 源代碼在 asterisk\apps\app_dial.c
跟蹤其關鍵代碼如下：

static int load_module(void)
{
	int res;

	res = ast_register_application_xml(app, dial_exec);
	res |= ast_register_application_xml(rapp, retrydial_exec);

	return res;
}

dial_exec
  dial_exec_full
    ast_request
    ast_call
    chan->tech->call  // 如: Dail(sip/6001) 將會調用 chan_sip 的call 函數

本文跟蹤 Dial（dahdi/1/s）的調用過程，實際上最終調用了 chan_dahdi 的call 函數。

static struct ast_channel_tech dahdi_tech = {
	.type = "DAHDI",
	...
	.call = dahdi_call,
	...
};

dahdi_call
  analog_call(p->sig_pvt, ast, rdest, timeout);
    analog_ring(p);
      my_ring(p);
        dahdi_ring_phone(p);
          x = DAHDI_ONHOOK;
	      res = ioctl(p->subs[SUB_REAL].dfd, DAHDI_HOOK, &x);
	      do {
		    x = DAHDI_RING;
		    res = ioctl(p->subs[SUB_REAL].dfd, DAHDI_HOOK, &x);
		 }
    

dahdi_call 最終調用 dahdi_ring_phone 函數，裏面
首先 用 ioctl DAHDI_HOOK DAHDI_ONHOOK 確保是掛機狀態
再 ioctl DAHDI_HOOK DAHDI_RING 發起振鈴

dahdi 驅動層對應代碼：
dahdi-base.c
dahdi_chan_ioctl 中

switch (j) {
			case DAHDI_ONHOOK:
				spin_lock_irqsave(&chan->lock, flags);
				dahdi_hangup(chan);      //掛機
				spin_unlock_irqrestore(&chan->lock, flags);
				break;
			case DAHDI_OFFHOOK:
				spin_lock_irqsave(&chan->lock, flags);
				if ((chan->txstate == DAHDI_TXSTATE_KEWL) ||
				  (chan->txstate == DAHDI_TXSTATE_AFTERKEWL)) {
					spin_unlock_irqrestore(&chan->lock, flags);
					return -EBUSY;
				}
				dahdi_rbs_sethook(chan, DAHDI_TXSIG_OFFHOOK, DAHDI_TXSTATE_DEBOUNCE, chan->debouncetime);
				spin_unlock_irqrestore(&chan->lock, flags);
				break;
			case DAHDI_RING:
			case DAHDI_START:
				spin_lock_irqsave(&chan->lock, flags);
				if (!chan->curzone) {
					spin_unlock_irqrestore(&chan->lock, flags);
					module_printk(KERN_WARNING, "Cannot start tone until a tone zone is loaded.\n");
					return -ENODATA;
				}
				if (chan->txstate != DAHDI_TXSTATE_ONHOOK) {
					spin_unlock_irqrestore(&chan->lock, flags);
					return -EBUSY;
				}
				if (chan->sig & __DAHDI_SIG_FXO) {
					ret = 0;
					chan->cadencepos = 0;
					ret = chan->ringcadence[0];
					dahdi_rbs_sethook(chan, DAHDI_TXSIG_START, DAHDI_TXSTATE_RINGON, ret);
				} else
					dahdi_rbs_sethook(chan, DAHDI_TXSIG_START, DAHDI_TXSTATE_START, chan->starttime);
				spin_unlock_irqrestore(&chan->lock, flags);
				if (file->f_flags & O_NONBLOCK)
					return -EINPROGRESS;
				break;

其中 dahdi_hangup 裏面也是調用 dahdi_rbs_sethook
dahdi_rbs_sethook 最終調用的是 wctdm_hooksig 。
wctdm_hooksig 中需要實現的是對 ONHOOK 、OFFHOOK、START(RING)的硬件層處理。

Q1.caller id 是怎麼發送的？

跟蹤 asterisk debug

[Jun 14 07:33:00] DEBUG[2741][C-00000001] rtp_engine.c: Can't find native functions for channel 'DAHDI/8-1'
[Jun 14 07:33:00] DEBUG[2741][C-00000001] sig_analog.c: CALLING CID_NAME: 8000 CID_NUM:: 8000
[Jun 14 07:33:00] DEBUG[2741][C-00000001] sig_analog.c: FXO: setup deferred dialstring: 12
[Jun 14 07:33:01] DEBUG[2741][C-00000001] channel.c: Channel DAHDI/8-1 setting read format path: ulaw -> ulaw
[Jun 14 07:33:01] DEBUG[2741][C-00000001] channel.c: Channel SIP/8000-00000000 setting write format path: ulaw -> ulaw
[Jun 14 07:33:01] DEBUG[2741][C-00000001] channel.c: Channel SIP/8000-00000000 setting read format path: ulaw -> ulaw
[Jun 14 07:33:01] DEBUG[2741][C-00000001] channel.c: Channel DAHDI/8-1 setting write format path: ulaw -> ulaw
[Jun 14 07:33:01] DEBUG[2724] devicestate.c: No provider found, checking channel drivers for DAHDI - 8
[Jun 14 07:33:01] DEBUG[2741][C-00000001] chan_sip.c: Trying to put 'SIP/2.0 180' onto UDP socket destined for 172.16.0.158:14894
[Jun 14 07:33:01] DEBUG[2724] devicestate.c: Changing state for DAHDI/8 - state 6 (Ringing)
[Jun 14 07:33:02] DEBUG[2741][C-00000001] sig_analog.c: analog_exception 8
[Jun 14 07:33:02] DEBUG[2741][C-00000001] sig_analog.c: Exception on 11, channel 8
[Jun 14 07:33:02] DEBUG[2741][C-00000001] sig_analog.c: __analog_handle_event 8
[Jun 14 07:33:02] DEBUG[2741][C-00000001] sig_analog.c: Got event ANALOG_EVENT_RINGEROFF(8) on channel 8 (index 0)
[Jun 14 07:33:02] DEBUG[2741][C-00000001] sig_analog.c: Sending callerid.  CID_NAME: '8000' CID_NUM: '8000'
[Jun 14 07:33:02] DEBUG[2741][C-00000001] chan_dahdi.c: Starting cid spill
[Jun 14 07:33:02] DEBUG[2741][C-00000001] chan_dahdi.c: writing callerid at pos 0 of 9267, res = 160
][Jun 14 07:33:02] DEBUG[2741][C-00000001] chan_dahdi.c: writing callerid at pos 160 of 9267, res = 160
[Jun 14 07:33:02] DEBUG[2741][C-00000001] chan_dahdi.c: writing callerid at pos 320 of 9267, res = 160
[Jun 14 07:33:02] DEBUG[2741][C-00000001] chan_dahdi.c: writing callerid at pos 480 of 9267, res = 160
[Jun 14 07:33:02] DEBUG[2741][C-00000001] chan_dahdi.c: writing callerid at pos 640 of 9267, res = -1

結合代碼可知：
asterisk 檢測到ANALOG_EVENT_RINGEROFF 的event 時，調用 analog_send_callerid 。

__analog_handle_event        //asterisk-16.0.0\channels\sig_analog.c
  case ANALOG_EVENT_RINGEROFF:
    analog_send_callerid(p, 0, &p->caller)
      analog_callbacks.send_callerid ()
        my_send_callerid
          send_callerid
            write(p->subs[SUB_REAL].dfd,...)        

最終是調用write 將數據寫入驅動，已經知道write 寫入的數據，在驅動中最終是通過pcm 發送出去。
由此推測callerrid 最終是轉化成了聲音數據，傳輸給模塊，這個聲音猜測是DTMF聲音，模塊端解碼DTMF數據可以得到callerid 。