modem: cmux: Implement Power Saving Control message

Signal powersaving mode for the remote end using PSC command.
Wakes up the remote end from powersaving mode by sending flag characters.

This method is defined in 3GPP TS 27.010.
Sections 5.4.6.3.2 Power Saving Control (PSC) and
5.4.7 Power Control and Wake-up Mechanisms.

Essentially it is one PSC command to indicate a sleep state, and
then repeated flag characters to wake up the remote end or indicate
that we are woken up.

As we now have so many state transitions, I refactored the internal
event bits to use set_state() and wait_state() so we don't need
two set of variables to maintain.

Signed-off-by: Seppo Takalo <[email protected]>

Author: SeppoTakalo

include/zephyr/modem/cmux.h

@@ -72,6 +72,10 @@ enum modem_cmux_state {
 	MODEM_CMUX_STATE_DISCONNECTED = 0,
 	MODEM_CMUX_STATE_CONNECTING,
 	MODEM_CMUX_STATE_CONNECTED,
+	MODEM_CMUX_STATE_ENTER_POWERSAVE,
+	MODEM_CMUX_STATE_POWERSAVE,
+	MODEM_CMUX_STATE_CONFIRM_POWERSAVE,
+	MODEM_CMUX_STATE_WAKEUP,
 	MODEM_CMUX_STATE_DISCONNECTING,
 };
 
@@ -187,6 +191,7 @@ struct modem_cmux {
 
 	/* Synchronize actions */
 	struct k_event event;
+	k_timepoint_t t3_timepoint;
 
 	/* Statistics */
 #if CONFIG_MODEM_STATS

subsys/modem/Kconfig

@@ -64,6 +64,14 @@ config MODEM_CMUX_WORK_BUFFER_SIZE_EXTRA
 	  Extra bytes to add to the work buffers used by the CMUX module.
 	  The default size of these buffers is MODEM_CMUX_MTU + 7 (CMUX header size).
 
+config MODEM_CMUX_T3_TIMEOUT
+	int "CMUX T3 timeout in seconds"
+	range 1 255
+	default 10
+	help
+	  Response Timer for wake-up procedure(T3).
+	  Time in seconds before the link is considered dead.
+
 module = MODEM_CMUX
 module-str = modem_cmux
 source "subsys/logging/Kconfig.template.log_config"