tests/usbus_msc: use emulated MTD as test mockup

tests/usbus_msc/Makefile

@@ -5,7 +5,7 @@ include ../Makefile.tests_common
  # This has to be the absolute path to the RIOT base directory:
 RIOTBASE ?= $(CURDIR)/../..
 
- # Comment this out to disable code in RIOT that does safety checking
+# Comment this out to disable code in RIOT that does safety checking
 # which is not needed in a production environment but helps in the
 # development process:
 DEVELHELP ?= 1
@@ -19,6 +19,11 @@ USEMODULE += shell
 USEMODULE += usbus_msc
 USEMODULE += ztimer_msec
 
+# If your board does not provide a MTD for testing, use the following line
+# to emulate an MTD with 64 sectors with 4 pages of 128 bytes each in RAM. You
+# can override these parameters by SECTOR_COUNT, PAGES_PER_SECTOR and PAGE_SIZE.
+# USEMODULE += mtd_emulated
+
 # Change this to 0 show compiler invocation lines by default:
 QUIET ?= 1
 

tests/usbus_msc/README.md

@@ -39,6 +39,19 @@ by attaching it to the host with the command:
 At this point, the USBUS stack will export the selected MTD devices.
 Devices should appears under /dev/sdX entries.
 
+If the board does not provide a MTD device, a MTD device can be emulated in RAM
+for testing using module `mtd_emulated`:
+```
+USEMODULE=mtd_emulated BOARD=... make ...
+```
+The emulated MTD device has by default 64 sectors with 4 pages of 128 bytes
+each, the minimum size to be able to create a partition with FAT file system.
+These default parameters can be overridden e.g. by `SECTOR_COUNT`,
+`PAGES_PER_SECTOR` and `PAGE_SIZE`:
+```
+CFLAGS='-DSECTOR_COUNT=128' USEMODULE=mtd_emulated BOARD=... make ...
+```
+
 **Notes:** Depending on the MTD device and the USB speed, this operation can take some times.
 
 USB operation can be stopped at any time using:

tests/usbus_msc/main.c

@@ -22,6 +22,32 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "board.h"
+
+#if defined(MODULE_MTD_EMULATED)
+
+#include "mtd_emulated.h"
+
+/* The following parameters are only suitable for testing the basic functions
+ * of USB MSC. To create a partition with a FAT file system, at least 64 sectors
+ * have to be used. */
+
+#ifndef SECTOR_COUNT
+#define SECTOR_COUNT        64
+#endif
+
+#ifndef PAGES_PER_SECTOR
+#define PAGES_PER_SECTOR    4
+#endif
+
+#ifndef PAGE_SIZE
+#define PAGE_SIZE           128
+#endif
+
+MTD_EMULATED_DEV(0, SECTOR_COUNT, PAGES_PER_SECTOR, PAGE_SIZE);
+
+#endif /* MODULE_MTD_EMULATED */
+
 #include "mtd_default.h"
 #include "shell.h"
 #include "usb/usbus.h"