Add M155 support for periodic temperature reporting

M155 turns on automatic periodic temperature reporting.

Enables live temperature reporting while waiting for temps (M119)
and during normal gcode processing without depending on M105 requests
from the host.

Also add "cap: AUTOREPORT_TEMP" capability report to M115. Octoprint
relies on this feature to determine if M155 is supported. Perhaps this
is a bug in Octoprint since M115 "cap" reporting is optional.

    Usage: M155 S<period> [P<sensor>]
     S specifies the period in seconds to report the temperatures
     P optionally specifies a 0-based sensor index to report

      S0 disables automatic reporting
      Omitting the P field reports on all sensors

    Example: M155 S5
       Causes Teacup to send a temperature report for all sensors
       every 5 seconds.

Ref: https://reprap.org/wiki/Firmware_Capabilities_Protocol

clock.c

@@ -94,6 +94,7 @@ static void clock_250ms(void) {
     #endif
 
     temp_residency_tick();
+    temp_periodic_print();
 
     if (temp_waiting()) {
       serial_writestr_P(PSTR("Waiting for target temp\n"));

gcode_process.c

@@ -644,7 +644,12 @@ void process_gcode_command() {
 				//?  FIRMWARE_NAME:Teacup FIRMWARE_URL:http://github.com/traumflug/Teacup_Firmware/ PROTOCOL_VERSION:1.0 MACHINE_TYPE:Mendel EXTRUDER_COUNT:1 TEMP_SENSOR_COUNT:1 HEATER_COUNT:1
 				//?
 
-				sersendf_P(PSTR("FIRMWARE_NAME:Teacup FIRMWARE_URL:http://github.com/traumflug/Teacup_Firmware/ PROTOCOL_VERSION:1.0 MACHINE_TYPE:Mendel EXTRUDER_COUNT:%d TEMP_SENSOR_COUNT:%d HEATER_COUNT:%d\n"), 1, NUM_TEMP_SENSORS, NUM_HEATERS);
+        sersendf_P(PSTR("FIRMWARE_NAME:Teacup "
+                        "FIRMWARE_URL:http://github.com/traumflug/Teacup_Firmware/ "
+                        "PROTOCOL_VERSION:1.0 MACHINE_TYPE:Mendel EXTRUDER_COUNT:%d "
+                        "TEMP_SENSOR_COUNT:%d HEATER_COUNT:%d\n"
+                        "cap:AUTOREPORT_TEMP:%d\n"),
+                        1, NUM_TEMP_SENSORS, NUM_HEATERS, 1);
 				break;
 
 			case 116:
@@ -790,6 +795,35 @@ void process_gcode_command() {
 				#endif
 				break;
 
+      case 155:
+        //? --- M155: Report Temperature(s) Periodically ---
+        //?
+        //? Example: M155 Sn
+        //?
+        //? turns on periodic reporting of the temperatures of the current
+        //? extruder and the build base in degrees Celsius. The reporting
+        //? interval is given in seconds as the S parameter. Use S0 to disable
+        //? periodic temperature reporting. The reporting format is the same
+        //? as for M105, except there is no "ok" at the start of each report.
+        //? For example, the line sent to the host periodically looks like
+        //?
+        //? <tt>T:201 B:117</tt>
+        //?
+        //? Teacup supports an optional P parameter as a zero-based temperature
+        //? sensor index to address.
+        //?
+
+        // S<period-seconds> is required
+        if ( ! next_target.seen_S)
+          break;
+        #ifdef ENFORCE_ORDER
+          queue_wait();
+        #endif
+        if ( ! next_target.seen_P)
+          next_target.P = TEMP_SENSOR_none;
+        temp_periodic_config(next_target.S, next_target.P);
+        break;
+
       case 220:
         //? --- M220: Set speed factor override percentage ---
         if ( ! next_target.seen_S)

temp.c

@@ -108,6 +108,11 @@ static struct {
 static uint8_t wait_for_temp = 0;
 
 
+// Automatic temperature report period (AUTOREPORT_TEMP)
+static uint8_t          periodic_temp_seconds;
+static temp_sensor_t    periodic_temp_index;
+static uint8_t          periodic_temp_timer;
+
 /// Set up temp sensors.
 void temp_init() {
 	temp_sensor_t i;
@@ -626,6 +631,27 @@ static void single_temp_print(temp_sensor_t index) {
   #endif
 }
 
+/// set parameters for periodic temperature reporting
+/// \param secs reporting interval in seconds; 0 to disable reporting
+/// \param index sensor to report
+void temp_periodic_config(uint8_t secs, temp_sensor_t index) {
+  periodic_temp_seconds = secs;
+  periodic_temp_index = index;
+  periodic_temp_timer = secs;
+}
+
+/// send temperatures to the host periodically.
+/// Called once per second from clock.c
+void temp_periodic_print() {
+  if (periodic_temp_seconds == 0)
+    return;
+  if (--periodic_temp_timer != 0)
+    return;
+
+  temp_print(periodic_temp_index);
+  periodic_temp_timer = periodic_temp_seconds;
+}
+
 /// send temperatures to host
 /// \param index sensor value to send
 void temp_print(temp_sensor_t index) {

temp.h

@@ -40,6 +40,9 @@ void temp_heater_tick(void);
 
 void temp_residency_tick(void);
 
+void temp_periodic_config(uint8_t secs, temp_sensor_t index);
+void temp_periodic_print(void);
+
 uint8_t	temp_achieved(void);
 
 void temp_set_wait(void);