update to lwIP-2.1.0: partial SACK support by default (de-selectable in menu) (#5126)

* update to lwIP-2.1.0rc1: partial SACK support
fix #4176

* hash fix

* get some flash back due to mistake in conf (fragmentation & reassembly was incorrectly enabled)
(ahah I scared you)

* add missing include files

* update to lwip-2.1.0(release) + remove unused lwIP's include files

* lwIP release 2.1.0, SACK is now default, bigger, no-SACK is selectable

* fix ldscript

* pio

* rename 'sack' option to 'feat'ure option, + IP fragmentation/reassembly

* merge, fix pio

* change internal/hidden string

* pio: more lwip2 configuration: + without sack for no change in flash footprint

tools/sdk/lwip2/include/lwip/apps/sntp_opts.h

@@ -38,6 +38,7 @@
 #define LWIP_HDR_APPS_SNTP_OPTS_H
 
 #include "lwip/opt.h"
+#include "lwip/prot/iana.h"
 
 /**
  * @defgroup sntp_opts Options
@@ -46,8 +47,10 @@
  */
 
 /** SNTP macro to change system time in seconds
- * Define SNTP_SET_SYSTEM_TIME_US(sec, us) to set the time in microseconds instead of this one
- * if you need the additional precision.
+ * Define SNTP_SET_SYSTEM_TIME_US(sec, us) to set the time in microseconds
+ * instead of this one if you need the additional precision. Alternatively,
+ * define SNTP_SET_SYSTEM_TIME_NTP(sec, frac) in order to work with native
+ * NTP timestamps instead.
  */
 #if !defined SNTP_SET_SYSTEM_TIME || defined __DOXYGEN__
 #define SNTP_SET_SYSTEM_TIME(sec)   LWIP_UNUSED_ARG(sec)
@@ -81,12 +84,7 @@
 
 /** SNTP server port */
 #if !defined SNTP_PORT || defined __DOXYGEN__
-#define SNTP_PORT                   123
-#endif
-
-/** Set this to 1 to allow config of SNTP server(s) by DNS name */
-#if !defined SNTP_SERVER_DNS || defined __DOXYGEN__
-#define SNTP_SERVER_DNS             0
+#define SNTP_PORT                   LWIP_IANA_PORT_SNTP
 #endif
 
 /** Sanity check:
@@ -96,7 +94,7 @@
  *        response comes from the server we sent the request to.
  * - >= 2 to check returned Originate Timestamp against Transmit Timestamp
  *        sent to the server (to ensure response to older request).
- * - >= 3 @todo: discard reply if any of the LI, Stratum, or Transmit Timestamp
+ * - >= 3 @todo: discard reply if any of the VN, Stratum, or Transmit Timestamp
  *        fields is 0 or the Mode field is not 4 (unicast) or 5 (broadcast).
  * - >= 4 @todo: to check that the Root Delay and Root Dispersion fields are each
  *        greater than or equal to 0 and less than infinity, where infinity is
@@ -107,6 +105,30 @@
 #define SNTP_CHECK_RESPONSE         0
 #endif
 
+/** Enable round-trip delay compensation.
+ * Compensate for the round-trip delay by calculating the clock offset from
+ * the originate, receive, transmit and destination timestamps, as per RFC.
+ *
+ * The calculation requires compiler support for 64-bit integers. Also, either
+ * SNTP_SET_SYSTEM_TIME_US or SNTP_SET_SYSTEM_TIME_NTP has to be implemented
+ * for setting the system clock with sub-second precision. Likewise, either
+ * SNTP_GET_SYSTEM_TIME or SNTP_GET_SYSTEM_TIME_NTP needs to be implemented
+ * with sub-second precision.
+ *
+ * Although not strictly required, it makes sense to combine this option with
+ * SNTP_CHECK_RESPONSE >= 2 for sanity-checking of the received timestamps.
+ * Also, in order for the round-trip calculation to work, the difference
+ * between the local clock and the NTP server clock must not be larger than
+ * about 34 years. If that limit is exceeded, the implementation will fall back
+ * to setting the clock without compensation. In order to ensure that the local
+ * clock is always within the permitted range for compensation, even at first
+ * try, it may be necessary to store at least the current year in non-volatile
+ * memory.
+ */
+#if !defined SNTP_COMP_ROUNDTRIP || defined __DOXYGEN__
+#define SNTP_COMP_ROUNDTRIP         0
+#endif
+
 /** According to the RFC, this shall be a random delay
  * between 1 and 5 minutes (in milliseconds) to prevent load peaks.
  * This can be defined to a random generation function,
@@ -114,33 +136,40 @@
  * Turned off by default.
  */
 #if !defined SNTP_STARTUP_DELAY || defined __DOXYGEN__
+#ifdef LWIP_RAND
+#define SNTP_STARTUP_DELAY          1
+#else
 #define SNTP_STARTUP_DELAY          0
 #endif
+#endif
 
 /** If you want the startup delay to be a function, define this
  * to a function (including the brackets) and define SNTP_STARTUP_DELAY to 1.
  */
 #if !defined SNTP_STARTUP_DELAY_FUNC || defined __DOXYGEN__
-#define SNTP_STARTUP_DELAY_FUNC     SNTP_STARTUP_DELAY
+#define SNTP_STARTUP_DELAY_FUNC     (LWIP_RAND() % 5000)
 #endif
 
 /** SNTP receive timeout - in milliseconds
  * Also used as retry timeout - this shouldn't be too low.
- * Default is 3 seconds.
+ * Default is 15 seconds. Must not be beolw 15 seconds by specification (i.e. 15000)
  */
 #if !defined SNTP_RECV_TIMEOUT || defined __DOXYGEN__
-#define SNTP_RECV_TIMEOUT           3000
+#define SNTP_RECV_TIMEOUT           15000
 #endif
 
 /** SNTP update delay - in milliseconds
- * Default is 1 hour. Must not be beolw 15 seconds by specification (i.e. 15000)
+ * Default is 1 hour. Must not be beolw 60 seconds by specification (i.e. 60000)
  */
 #if !defined SNTP_UPDATE_DELAY || defined __DOXYGEN__
 #define SNTP_UPDATE_DELAY           3600000
 #endif
 
 /** SNTP macro to get system time, used with SNTP_CHECK_RESPONSE >= 2
- * to send in request and compare in response.
+ * to send in request and compare in response. Also used for round-trip
+ * delay compensation if SNTP_COMP_ROUNDTRIP != 0.
+ * Alternatively, define SNTP_GET_SYSTEM_TIME_NTP(sec, frac) in order to
+ * work with native NTP timestamps instead.
  */
 #if !defined SNTP_GET_SYSTEM_TIME || defined __DOXYGEN__
 #define SNTP_GET_SYSTEM_TIME(sec, us)     do { (sec) = 0; (us) = 0; } while(0)
@@ -166,6 +195,13 @@
 #define SNTP_RETRY_TIMEOUT_EXP      1
 #endif
 
+/** Keep a reachability shift register per server
+ * Default is on to conform to RFC.
+ */
+#if !defined SNTP_MONITOR_SERVER_REACHABILITY || defined __DOXYGEN__
+#define SNTP_MONITOR_SERVER_REACHABILITY 1
+#endif
+
 /**
  * @}
  */