Add semihosting support for nrf52 devices (#4137)

* Turn off vscode cmake prompt - we don't use cmake on meshtastic

* Add rak4631_dap variant for debugging with NanoDAP debug probe device.

* The rak device can also run freertos (which is underneath nrf52 arduino)

* Add semihosting support for nrf52840 devices
Initial platformio.ini file only supports rak4630
Default to non TCP for the semihosting log output for now...
Fixes https://github.com/meshtastic/firmware/issues/4135

* fix my botched merge - keep board_level = extra flag for rak3631_dbg

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/DebugConfiguration.h

@@ -25,6 +25,14 @@
 
 #include "SerialConsole.h"
 
+// If defined we will include support for ARM ICE "semihosting" for a virtual
+// console over the JTAG port (to replace the normal serial port)
+// Note: Normally this flag is passed into the gcc commandline by platformio.ini.
+// for an example see env:rak4631_dap.
+// #ifndef USE_SEMIHOSTING
+// #define USE_SEMIHOSTING
+// #endif
+
 #define DEBUG_PORT (*console) // Serial debug port
 
 #ifdef USE_SEGGER

src/platform/nrf52/main-nrf52.cpp

@@ -149,13 +149,43 @@ void nrf52Loop()
     checkSDEvents();
 }
 
+#ifdef USE_SEMIHOSTING
+#include <SemihostingStream.h>
+
+/**
+ * Note: this variable is in BSS and therfore false by default.  But the gdbinit
+ * file will be installing a temporary breakpoint that changes wantSemihost to true.
+ */
+bool wantSemihost;
+
+/**
+ * Turn on semihosting if the ICE debugger wants it.
+ */
+void nrf52InitSemiHosting()
+{
+    if (wantSemihost) {
+        static SemihostingStream semiStream;
+        // We must dynamically alloc because the constructor does semihost operations which
+        // would crash any load not talking to a debugger
+        semiStream.open();
+        semiStream.println("Semihosting starts!");
+        // Redirect our serial output to instead go via the ICE port
+        console->setDestination(&semiStream);
+    }
+}
+#endif
+
 void nrf52Setup()
 {
-    auto why = NRF_POWER->RESETREAS;
+    uint32_t why = NRF_POWER->RESETREAS;
     // per
     // https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.nrf52832.ps.v1.1%2Fpower.html
     LOG_DEBUG("Reset reason: 0x%x\n", why);
 
+#ifdef USE_SEMIHOSTING
+    nrf52InitSemiHosting();
+#endif
+
     // Per
     // https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/monitor-mode-debugging-with-j-link-and-gdbeclipse
     // This is the recommended setting for Monitor Mode Debugging