arch/delays: Set invalid default value for BOARD_LOOPSPERMSEC

To resolve #17004, this commit sets the default Kconfig value for
CONFIG_BOARD_LOOPSPERMSEC as -1, which is invalid. It statically asserts
at compile time that the value is greater than or equal to 0 so that the
user is notified if their board/configuration does not yet have a
calibrated value for this configuration option. The user is directed to
set a non-negative value and then later calibrate with `calib_udelay`.

Signed-off-by: Matteo Golin <matteo.golin@gmail.com>

Author: linguini1

arch/Kconfig

@@ -1274,11 +1274,12 @@ comment "Board Settings"
 
 config BOARD_LOOPSPERMSEC
 	int "Delay loops per millisecond"
-	default 5000
+	default -1
 	---help---
 		Simple delay loops are used by some logic, especially during boot-up,
-		driver initialization.  These delay loops must be calibrated for each
-		board in order to assure accurate timing by the delay loops.
+		driver initialization. These delay loops must be calibrated for each
+		board in order to assure accurate timing by the delay loops. You can
+		do so with `calib_udelay` (EXAMPLES_CALIB_UDELAY).
 
 comment "Interrupt options"
 

include/nuttx/arch.h

@@ -99,6 +99,18 @@
 #define DEBUGPOINT_BREAKPOINT    0x04
 #define DEBUGPOINT_STEPPOINT     0x05
 
+/* Ensure that LOOPSPERMSEC is not the default, invalid value. If it is, let
+ * the user know that they need to change it and then calibrate it.
+ */
+
+static_assert(
+    CONFIG_BOARD_LOOPSPERMSEC >= 0,
+    "Please set a non-negative value for CONFIG_BOARD_LOOPSPERMSEC to pass "
+    "compilation. It is recommended that after your initial build, you use "
+    "the example 'calib_udelay' to get a precise value for this option. "
+    "Please search the NuttX documentation for CONFIG_BOARD_LOOPSPERMSEC for "
+    "more information.");
+
 /****************************************************************************
  * Name: up_cpu_index
  *