From: Lars Poeschel <[email protected]>
Add some words about modem control lines, DCD signal and that
an open may block to the n_gsm documentation.
Signed-off-by: Lars Poeschel <[email protected]>
---
Documentation/serial/n_gsm.txt | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/Documentation/serial/n_gsm.txt b/Documentation/serial/n_gsm.txt
index a5d9112..089b934 100644
--- a/Documentation/serial/n_gsm.txt
+++ b/Documentation/serial/n_gsm.txt
@@ -74,6 +74,12 @@ done
for example, it's possible :
- and to use gnokii to send / receive SMS on ttygsm1
- to use ppp to establish a datalink on ttygsm2
+- If you want to use a virtual muxed channel in your own programs, be aware
+ that it respects the modem control lines. If you open the virtual port it
+ will block, if it is not connected to a carrier (DCD signal missing). You
+ could open the virtual port with O_NDELAY flag and do normal AT commands
+ to the modem without a carrier. You can change to blocking mode later if
+ you need this with fcntl F_SETFL/F_GETFL.
6- first close all virtual ports before closing the physical port.
--
1.8.5.2