boards/sim: Add a xipfs configuration.

rammtd answers BIOC_XIPBASE with the base of its RAM buffer, so it is a
usable stand-in for memory mapped NOR: extents are directly addressable and
the in-place mmap path can be exercised end to end without any flash.  Mount
xipfs on it when it is the configured file system, and add a configuration
that runs the xipfs test suite, fault injection included.

Assisted-by: Claude Code:claude-opus-5
Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>

boards/sim/sim/sim/configs/xipfs/defconfig

@@ -0,0 +1,33 @@
+#
+# This file is autogenerated: PLEASE DO NOT EDIT IT.
+#
+# You can use "make menuconfig" to make any modifications to the installed .config file.
+# You can then do "make savedefconfig" to generate a new defconfig file that includes your
+# modifications.
+#
+CONFIG_ARCH="sim"
+CONFIG_ARCH_BOARD="sim"
+CONFIG_ARCH_BOARD_SIM=y
+CONFIG_ARCH_CHIP="sim"
+CONFIG_ARCH_SIM=y
+CONFIG_BOARDCTL_POWEROFF=y
+CONFIG_BOARD_LOOPSPERMSEC=0
+CONFIG_BUILTIN=y
+CONFIG_DEBUG_SYMBOLS=y
+CONFIG_FS_PROCFS=y
+CONFIG_FS_XIPFS=y
+CONFIG_FS_XIPFS_FAULT_INJECT=y
+CONFIG_IDLETHREAD_STACKSIZE=8192
+CONFIG_INIT_ENTRYPOINT="nsh_main"
+CONFIG_LIBC_STRERROR=y
+CONFIG_MTD=y
+CONFIG_NSH_BUILTIN_APPS=y
+CONFIG_NSH_READLINE=y
+CONFIG_RAMMTD=y
+CONFIG_RAMMTD_FLASHSIM=y
+CONFIG_SCHED_WAITPID=y
+CONFIG_START_MONTH=6
+CONFIG_START_YEAR=2008
+CONFIG_SYSTEM_NSH=y
+CONFIG_SYSTEM_XIPFS=y
+CONFIG_TESTING_FS_XIPFS=y

boards/sim/sim/sim/src/sim_bringup.c

@@ -212,6 +212,22 @@ int sim_bringup(void)
 
           smart_initialize(0, mtd, NULL);
 
+#elif defined(CONFIG_FS_XIPFS)
+          /* Mount the XIPFS file system.  rammtd answers BIOC_XIPBASE with
+           * the base of its RAM buffer, which makes it a usable stand-in
+           * for memory mapped NOR: extents are directly addressable, so
+           * the XIP mmap path can be exercised end to end.
+           */
+
+          ret = nx_mount("/dev/rammtd", "/mnt/xipfs", "xipfs", 0,
+                         "autoformat");
+          if (ret < 0)
+            {
+              syslog(LOG_ERR,
+                     "ERROR: Failed to mount XIPFS at /mnt/xipfs: %d\n",
+                     ret);
+            }
+
 #elif defined(CONFIG_FS_SPIFFS)
           /* Mount the SPIFFS file system */