Re: ZTE modem problems and workrounds

[Rick Jones <rick activeservice co uk>]

--On Tuesday, July 07, 2009 00:03:49 +0100 Rick Jones <rick activeservice co uk> wrote:
> 
> I find that about one time in 4 or 5 it doesn't detect any port as a modem, but unplug/re-plug and it usually gets it. I think this is probably because the probe responses get masked by the stream of UMs coming out (+ZUSIMR:2), these need to be killed off by sending +CPMS?. This has to be done anyway to get the thing to dial reliably - I rely on an external script to do it at the moment, but it's not ideal. Would it be feasible for nm-modem-probe to do this?
> 
> There is another problem with the serial port termios modes, AFAICT, NM doesn't set them up, but neither does the Option driver. They can have an arbitrary state which results in unpredictable behaviour, and even kernel panics.


OK, I retract that, having looked at the source code!

It's strange, but when trying to get concrete symptoms from the previous erratic behaviour, I was certain that running "stty raw" on each port improved the way it worked. Must have been an illusion.

However, I've looked at nm-modem-probe, and tried a patch which seems to work quite well - diff is attached.

It sends an initialisation to the modem before trying the various tests, this is "AT E0 +CPMS". Turning off echo reduces the clutter in the responses, and +CPMS is ZTE-specific to stop it emitting continuous UMs, which just get in the way of everything. +CPMS is actually invalid, but has the right effect, and should be benign on any other modem.

I also removed the \n from the modem commands, again it reduces response clutter (the modem takes \r as command terminator). However, maybe \r\n is needed for other modems? I don't know.

With this patch I now get 100% modem detection, and connection on the first or second try. That is a HUGE improvement!

Rick




--- nm-modem-probe-orig.c	2009-07-06 15:36:36.000000000 +0100
+++ nm-modem-probe.c	2009-07-07 12:24:15.000000000 +0100
@@ -329,6 +329,15 @@
 		timeout_ms -= 500;
 	}
 
+	/* PATCH - turn off echo and send +CPMS to stop ZTE +ZUSIMR messages */
+	if (modem_send_command (fd, "AT E0 +CPMS\r"))
+	{
+		const char *null_responses[] = { NULL };
+		/* we expect ERROR response! */
+		modem_wait_reply (fd, 2, null_responses, terminators, &term_idx, &reply);
+	}
+	/* END PATCH */
+
 	/* Standard response timeout case */
 	timeout_ms += 3000;
 
@@ -339,7 +348,7 @@
 		g_get_current_time (&start);
 
 		idx = term_idx = 0;
-		send_success = modem_send_command (fd, "AT+GCAP\r\n");
+		send_success = modem_send_command (fd, "AT+GCAP\r");
 		if (send_success)
 			idx = modem_wait_reply (fd, 2, gcap_responses, terminators, &term_idx, &reply);
 		else
@@ -391,7 +400,7 @@
 		reply = NULL;
 
 		verbose ("GCAP failed, trying ATI...");
-		if (modem_send_command (fd, "ATI\r\n")) {
+		if (modem_send_command (fd, "ATI\r")) {
 			idx = modem_wait_reply (fd, 3, ati_responses, terminators, &term_idx, &reply);
 			if (0 == term_idx && 0 == idx) {
 				verbose ("ATI response: %s", reply);
@@ -410,7 +419,7 @@
 	if ((idx != -2) && !(ret & MODEM_CAP_GSM) && !(ret & MODEM_CAP_IS707_A)) {
 		const char *cgmm_responses[] = { CGMM_TAG, NULL };
 
-		if (modem_send_command (fd, "AT+CGMM\r\n")) {
+		if (modem_send_command (fd, "AT+CGMM\r")) {
 			idx = modem_wait_reply (fd, 5, cgmm_responses, terminators, &term_idx, &reply);
 			if (0 == term_idx && 0 == idx) {
 				verbose ("CGMM response: %s", reply);