diff --git a/Marlin/Conditionals.h b/Marlin/Conditionals.h
index 34c58ca214488b9642cad6119dbb5f7a20655e6a..c70c84ca70bdbf6a2e3211d85fcec0dad8fd2979 100644
--- a/Marlin/Conditionals.h
+++ b/Marlin/Conditionals.h
@@ -397,8 +397,8 @@
/**
* Host keep alive
*/
- #ifndef HOST_KEEPALIVE_INTERVAL
- #define HOST_KEEPALIVE_INTERVAL 2
+ #ifndef DEFAULT_KEEPALIVE_INTERVAL
+ #define DEFAULT_KEEPALIVE_INTERVAL 2
#endif
/**
diff --git a/Marlin/Configuration.h b/Marlin/Configuration.h
index 157f7a5ac1f762585cb86ed2d8376396dcdf8b53..c45f6fcf3c73851845c8b5e29a96f9bf0aaad5c9 100644
--- a/Marlin/Configuration.h
+++ b/Marlin/Configuration.h
@@ -736,8 +736,8 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
-#define HOST_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index 6ce0ce6b6a683ac6fe23713033d150218726648f..45907f35573792038bc3cf389ae6e793f353fbeb 100644
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -488,7 +488,7 @@ static bool send_ok[BUFSIZE];
static MarlinBusyState busy_state = NOT_BUSY;
static millis_t next_busy_signal_ms = 0;
- uint8_t host_keepalive_interval = HOST_KEEPALIVE_INTERVAL;
+ uint8_t host_keepalive_interval = DEFAULT_KEEPALIVE_INTERVAL;
#define KEEPALIVE_STATE(n) do{ busy_state = n; }while(0)
#else
#define host_keepalive() ;
diff --git a/Marlin/example_configurations/Felix/Configuration.h b/Marlin/example_configurations/Felix/Configuration.h
index 57292b218e3a5e7f42689f6a6f2745ebab16dd50..a705f6531539bdb12ab28c0a6f5069728923462d 100644
--- a/Marlin/example_configurations/Felix/Configuration.h
+++ b/Marlin/example_configurations/Felix/Configuration.h
@@ -716,13 +716,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/Hephestos/Configuration.h b/Marlin/example_configurations/Hephestos/Configuration.h
index 4bf40859faccb4e193070b31996d99f9c36f8907..de0375c3becb0f9240e59e86bb99e6ffba3a3309 100644
--- a/Marlin/example_configurations/Hephestos/Configuration.h
+++ b/Marlin/example_configurations/Hephestos/Configuration.h
@@ -725,13 +725,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = true; // set to true to invert the lo
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/Hephestos_2/Configuration.h b/Marlin/example_configurations/Hephestos_2/Configuration.h
index 285ffb536f22c9b319f52c940bb9a53951ba935d..24a61f962e919a6add93ade5e59eeeaf911955aa 100644
--- a/Marlin/example_configurations/Hephestos_2/Configuration.h
+++ b/Marlin/example_configurations/Hephestos_2/Configuration.h
@@ -727,13 +727,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/K8200/Configuration.h b/Marlin/example_configurations/K8200/Configuration.h
index 17290bc875a224b370a013e4b8c682c7f0eff66f..81a01062d97f24ec89d8422fc7abf042d9dc5a4a 100644
--- a/Marlin/example_configurations/K8200/Configuration.h
+++ b/Marlin/example_configurations/K8200/Configuration.h
@@ -750,13 +750,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/RepRapWorld/Megatronics/Configuration.h b/Marlin/example_configurations/RepRapWorld/Megatronics/Configuration.h
index 22d7766191393bd79fcbf3170d6690f3d88273fe..95c14b1ce8747f0e0e38251425c5f37461c3f74c 100644
--- a/Marlin/example_configurations/RepRapWorld/Megatronics/Configuration.h
+++ b/Marlin/example_configurations/RepRapWorld/Megatronics/Configuration.h
@@ -733,13 +733,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/RigidBot/Configuration.h b/Marlin/example_configurations/RigidBot/Configuration.h
index 42a086495a2132e1c0b0fcb2612c4ef3fa7b62e0..60eb579e21ffdf783ccb1df3f2b53288083666a6 100644
--- a/Marlin/example_configurations/RigidBot/Configuration.h
+++ b/Marlin/example_configurations/RigidBot/Configuration.h
@@ -728,13 +728,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/SCARA/Configuration.h b/Marlin/example_configurations/SCARA/Configuration.h
index 4bc60ac2aa1b66e281bbc01c15e2145cc26b7d86..460479fcff1187cb4ded4ba0e3d2e054962d463f 100644
--- a/Marlin/example_configurations/SCARA/Configuration.h
+++ b/Marlin/example_configurations/SCARA/Configuration.h
@@ -741,13 +741,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/TAZ4/Configuration.h b/Marlin/example_configurations/TAZ4/Configuration.h
index 7b52693b94a69fedcd326a3c0732c0beefac5445..f8d760cc75144979f4a067624ec9f7b65374d362 100644
--- a/Marlin/example_configurations/TAZ4/Configuration.h
+++ b/Marlin/example_configurations/TAZ4/Configuration.h
@@ -754,13 +754,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/WITBOX/Configuration.h b/Marlin/example_configurations/WITBOX/Configuration.h
index aecbdc75d15c58f73bbbfc6cc09f75857c10bab9..7b67831d5f3f4f9a857164ba877ba8192090e2de 100644
--- a/Marlin/example_configurations/WITBOX/Configuration.h
+++ b/Marlin/example_configurations/WITBOX/Configuration.h
@@ -725,13 +725,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = true; // set to true to invert the lo
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/adafruit/ST7565/Configuration.h b/Marlin/example_configurations/adafruit/ST7565/Configuration.h
index 5eb8301be56b4b8f70a3bd7e09a3f5e744d91d81..0a0d9f21f0c6941d5681a1f02b16b3750e0044f8 100644
--- a/Marlin/example_configurations/adafruit/ST7565/Configuration.h
+++ b/Marlin/example_configurations/adafruit/ST7565/Configuration.h
@@ -733,13 +733,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/delta/biv2.5/Configuration.h b/Marlin/example_configurations/delta/biv2.5/Configuration.h
index 6cbb21ae51166c57c88691fdb9d7640461cad8d5..c827fb0c1dc7e821d57576b0bdd85732c911f5a3 100644
--- a/Marlin/example_configurations/delta/biv2.5/Configuration.h
+++ b/Marlin/example_configurations/delta/biv2.5/Configuration.h
@@ -862,13 +862,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = true; // set to true to invert the lo
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/delta/generic/Configuration.h b/Marlin/example_configurations/delta/generic/Configuration.h
index e6f049528ad0605baa5231aeb0b639d0a23ff8fe..75e8d0434121f0af573b158da2624ea2bbcae930 100644
--- a/Marlin/example_configurations/delta/generic/Configuration.h
+++ b/Marlin/example_configurations/delta/generic/Configuration.h
@@ -862,13 +862,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = true; // set to true to invert the lo
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/delta/kossel_mini/Configuration.h b/Marlin/example_configurations/delta/kossel_mini/Configuration.h
index e55d2941ee59275b218b4e6c830a0fdc1cfa13c0..2d2585e953f3e19863dcf3895ff3ac27986440bc 100644
--- a/Marlin/example_configurations/delta/kossel_mini/Configuration.h
+++ b/Marlin/example_configurations/delta/kossel_mini/Configuration.h
@@ -866,13 +866,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/delta/kossel_pro/Configuration.h b/Marlin/example_configurations/delta/kossel_pro/Configuration.h
index 61c6eee00837611d626453163c67faa5b50dbbbc..6a548b65e259fdf74d73d29576083b766fcda288 100644
--- a/Marlin/example_configurations/delta/kossel_pro/Configuration.h
+++ b/Marlin/example_configurations/delta/kossel_pro/Configuration.h
@@ -859,13 +859,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/delta/kossel_xl/Configuration.h b/Marlin/example_configurations/delta/kossel_xl/Configuration.h
index 37240d13680e2aea0faa5e261938f0acbe089534..cf8aefe8ed921dd27e830e56a0e4fee17ac79746 100644
--- a/Marlin/example_configurations/delta/kossel_xl/Configuration.h
+++ b/Marlin/example_configurations/delta/kossel_xl/Configuration.h
@@ -867,13 +867,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/makibox/Configuration.h b/Marlin/example_configurations/makibox/Configuration.h
index 3d21ed402aaaa8ea5ec42b9d688217ff96e62f1b..4e1ea0e646721cea97793ce137f59beb72646ac9 100644
--- a/Marlin/example_configurations/makibox/Configuration.h
+++ b/Marlin/example_configurations/makibox/Configuration.h
@@ -736,13 +736,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the l
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher
diff --git a/Marlin/example_configurations/tvrrug/Round2/Configuration.h b/Marlin/example_configurations/tvrrug/Round2/Configuration.h
index 32bfc9cd04d398d66df9271faa0c24ddd96031c8..2e4969c6eb89cec5ea26135253011386e34057d8 100644
--- a/Marlin/example_configurations/tvrrug/Round2/Configuration.h
+++ b/Marlin/example_configurations/tvrrug/Round2/Configuration.h
@@ -727,13 +727,11 @@ const bool Z_MIN_PROBE_ENDSTOP_INVERTING = true; // set to true to invert the lo
//
// Host Keepalive
//
-// By default Marlin will send a busy status message to the host
+// When enabled Marlin will send a busy status message to the host
// every couple of seconds when it can't accept commands.
//
-//#define DISABLE_HOST_KEEPALIVE // Enable this option if your host doesn't like keepalive messages.
-#if DISABLED(DISABLE_HOST_KEEPALIVE)
- #define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
-#endif
+#define HOST_KEEPALIVE_FEATURE // Disable this if your host doesn't like keepalive messages
+#define DEFAULT_KEEPALIVE_INTERVAL 2 // Number of seconds between "busy" messages. Set with M113.
//
// M100 Free Memory Watcher