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. It's a
thing Marlin does and Octorprint needs to see it before it will use
M155.

Usage: M155 S<period> [P<probe>]
 S specifies the period in seconds to report the temperatures
 P optionally specifies which sensor to report

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

clock.c

@@ -95,6 +95,8 @@ static void clock_250ms(void) {
 
     temp_residency_tick();
 
+    temp_periodic_print();
+
     if (temp_waiting()) {
       serial_writestr_P(PSTR("Waiting for target temp\n"));
       wait_for_temp = 1;

gcode_process.c

@@ -702,7 +702,12 @@ 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:
@@ -848,6 +853,35 @@ 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 +108,13 @@ static struct {
 static uint8_t wait_for_temp = 0;
 
 
+// How often to report temperature automatically
+static uint8_t          periodic_seconds;
+static temp_sensor_t    periodic_index;
+
+// Count time between temperature reports
+static uint8_t          periodic_timer;
+
 /// Set up temp sensors.
 void temp_init() {
 	temp_sensor_t i;
@@ -626,6 +633,27 @@ 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_seconds = secs;
+  periodic_index = index;
+  periodic_timer = secs;
+}
+
+/// send temperatures to the host periodically.
+/// Called once per second from clock.c
+void temp_periodic_print() {
+  if (periodic_seconds == 0)
+    return;
+  if (--periodic_timer != 0)
+    return;
+
+  temp_print(periodic_index);
+  periodic_timer = periodic_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);