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+# Getting started with the Mbed OS file system
+
+This example demonstrates how to use the Mbed OS file system.
+
+You can find more information about the Mbed OS file system and other related pieces of the Mbed OS storage stack [in the storage overview](https://os.mbed.com/docs/latest/reference/storage.html).
+
+**Table of contents:**
+
+1. [Hardware requirements](#hardware-requirements)
+1. [Usage](#usage)
+   - [Import the example](#import-the-example)
+   - [Compile the example](#compile-the-example)
+   - [Run the example](#run-the-example)
+   - [Troubleshooting](#troubleshooting)
+1. [Changing the file system](#changing-the-file-system)
+1. [Changing the block device](#changing-the-block-device)
+1. [Tested configurations](#tested-configurations)
+
+## Hardware requirements
+
+This example uses a block device as storage. This can be one of:
+
+* A built-in SPI flash, such as on the [FRDM-K82F](https://os.mbed.com/platforms/FRDM-K82F/).
+* An external block device (one of SPI flash, DataFlash or an SD card). 
+* Simulated on a heap block device on boards with enough RAM.
+
+This example uses an instance of the LittleFileSystem API (LittleFS) on external SPI flash.
+The [changing the block device](#changing-the-block-device) section describes
+how to change the file system or block device in the example.
+
+## Usage
+
+#### Import the example
+
+Make sure you have an Mbed development environment set up. [Get started with Mbed OS](https://os.mbed.com/docs/latest/tutorials/mbed-os-quick-start.html)
+to set everything up.
+
+From the command-line, import the example:
+
+```
+mbed import mbed-os-example-filesystem
+cd mbed-os-example-filesystem
+```
+
+#### Compile the example
+
+Invoke `mbed compile`, and specify the name of your platform and your favorite
+toolchain (`GCC_ARM`, `ARM`, `IAR`). For example, for the ARM Compiler 5:
+
+```
+mbed compile -m K64F -t ARM
+```
+
+Your PC may take a few minutes to compile your code. At the end, you see the
+following result:
+
+```
+[snip]
++--------------------------+-------+-------+-------+
+| Module                   | .text | .data |  .bss |
++--------------------------+-------+-------+-------+
+| Fill                     |   164 |     0 |  2136 |
+| Misc                     | 54505 |  2556 |   754 |
+| drivers                  |   640 |     0 |    32 |
+| features/filesystem      | 15793 |     0 |   550 |
+| features/storage         |    42 |     0 |   184 |
+| hal                      |   418 |     0 |     8 |
+| platform                 |  2355 |    20 |   582 |
+| rtos                     |   135 |     4 |     4 |
+| rtos/rtx                 |  5861 |    20 |  6870 |
+| targets/TARGET_Freescale |  8382 |    12 |   384 |
+| Subtotals                | 88295 |  2612 | 11504 |
++--------------------------+-------+-------+-------+
+Allocated Heap: 24576 bytes
+Allocated Stack: unknown
+Total Static RAM memory (data + bss): 14116 bytes
+Total RAM memory (data + bss + heap + stack): 38692 bytes
+Total Flash memory (text + data + misc): 91947 bytes
+
+Image: ./BUILD/K64F/ARM/mbed-os-example-filesystem.bin
+```
+
+#### Run the example
+
+1. Connect your Mbed Enabled device to the computer over USB.
+1. Copy the binary file to the Mbed Enabled device.
+1. Press the reset button to start the program.
+1. Open the UART of the board in your favorite UART viewing program. For
+   example, `screen /dev/ttyACM0`.
+   
+**Note:** The default serial port baud rate is 9600 bit/s.
+
+Expected output:
+
+```
+--- Mbed OS filesystem example ---
+Mounting the filesystem... Fail :(
+No filesystem found, formatting... OK
+Opening "/fs/numbers.txt"... Fail :(
+No file found, creating a new file... OK
+Writing numbers (10/10)... OK
+Seeking file... OK
+Incrementing numbers (10/10)... OK
+Closing "/fs/numbers.txt"... OK
+Opening the root directory... OK
+root directory:
+    .
+    ..
+    numbers.txt
+Closing the root directory... OK
+Opening "/fs/numbers.txt"...OK
+numbers:
+    1
+    2
+    3
+    4
+    5
+    6
+    7
+    8
+    9
+    10
+Closing "/fs/numbers.txt"... OK
+Unmounting... OK
+Mbed OS filesystem example done!
+```
+
+You can also reset the board to see the data persist across boots. Each boot
+increments the numbers stored on disk:
+
+```
+--- Mbed OS filesystem example ---
+Mounting the filesystem... OK
+Opening "/fs/numbers.txt"... OK
+Incrementing numbers (10/10)... OK
+Closing "/fs/numbers.txt"... OK
+Opening the root directory... OK
+root directory:
+    .
+    ..
+    numbers.txt
+Closing the root directory... OK
+Opening "/fs/numbers.txt"...OK
+numbers:
+    2
+    3
+    4
+    5
+    6
+    7
+    8
+    9
+    10
+    11
+Closing "/fs/numbers.txt"... OK
+Unmounting... OK
+Mbed OS filesystem example done!
+```
+
+If you find yourself with a corrupted file system, you can reset the storage
+by pressing BUTTON1:
+
+```
+Initializing the block device... OK
+Erasing the block device... OK
+Deinitializing the block device... OK
+```
+
+Note that if you press the reset button at the wrong time, you may corrupt
+a file system that is not power resilient!
+
+#### Troubleshooting
+
+If you have problems, you can review the [documentation](https://os.mbed.com/docs/latest/tutorials/debugging.html)
+for suggestions on what could be wrong and how to fix it.
+
+## Changing the file system
+
+In Mbed OS, a C++ classes that inherits from the [FileSystem](https://os.mbed.com/docs/latest/reference/storage.html#declaring-a-file-system)
+interface represents each file system. You can change the file system in the
+example by changing the class declared in main.cpp.
+
+``` diff
+- LittleFileSystem fs("fs");
++ FATFileSystem fs("fs");
+```
+
+**Note:** Different file systems require different minimum numbers of storage
+blocks to function. For the `FATFileSystem`, this example requires a minimum of
+256 blocks, and for the `LittleFileSystem`, this example requires a minimum of 6
+blocks. You can find the number of blocks on a block device by dividing the
+block device's size by its erase size.
+
+Mbed OS has two options for the file system:
+
+- [**LittleFileSystem**](https://os.mbed.com/docs/latest/reference/littlefilesystem.html) -
+  The little file system is a fail-safe file system we designed
+  for embedded systems, specifically for microcontrollers that use flash
+  storage.
+  
+  ``` cpp
+  LittleFileSystem fs("fs");
+  ```
+
+  - **Bounded RAM/ROM** - This file system works with a limited amount of memory.
+    It avoids recursion and limits dynamic memory to configurable
+    buffers.
+  
+  - **Power-loss resilient** - We designed this for operating systems
+    that may have random power failures. It has strong copy-on-write
+    guarantees and keeps storage on disk in a valid state.
+  
+  - **Wear leveling** - Because the most common form of embedded storage is
+    erodible flash memories, this file system provides a form of dynamic wear
+    leveling for systems that cannot fit a full flash translation layer.
+
+- **FATFileSystem** - The FAT file system is a well-known file system that you
+  can find on almost every system, including PCs. The Mbed OS implementation of
+  the FAT file system is based on ChanFS and is optimized for small embedded systems.
+  
+  ``` cpp
+  FATFileSystem fs("fs");
+  ```
+
+  - **Portable** - Almost every operating system supports the FAT file system,
+    which is the most common file system found on portable storage, such as SD
+    cards and flash drives. The FAT file system is the easiest way to support
+    access from a PC.
+
+## Changing the block device
+
+In Mbed OS, a C++ classes that inherits from the [BlockDevice](https://os.mbed.com/docs/latest/reference/storage.html#block-devices)
+interface represents each block device. You can change the filesystem in the
+example by changing the class declared in main.cpp.
+
+``` diff
+-SPIFBlockDevice bd(
+-        MBED_CONF_SPIF_DRIVER_SPI_MOSI,
+-        MBED_CONF_SPIF_DRIVER_SPI_MISO,
+-        MBED_CONF_SPIF_DRIVER_SPI_CLK,
+-        MBED_CONF_SPIF_DRIVER_SPI_CS);
++SDBlockDevice bd(
++        MBED_CONF_SD_SPI_MOSI,
++        MBED_CONF_SD_SPI_MISO,
++        MBED_CONF_SD_SPI_CLK,
++        MBED_CONF_SD_SPI_CS);
+```
+
+**Note:** Most block devices require pin assignments. Double check that the
+pins in `<driver>/mbed_lib.json` are correct. For example, to change the pins for the SD driver, open `sd-driver/config/mbed_lib.json`, and change your target platform to the correct pin-out in the `target_overrides` configuration:
+
+```
+   "target_overrides": {
+         ...
+         "NUCLEO_F429ZI": {
+             "SPI_MOSI": "PC_12",
+             "SPI_MISO": "PC_11",
+             "SPI_CLK":  "PC_10",
+             "SPI_CS":   "PA_15"
+         },
+         ...
+     }
+```
+The pins macros define above can be override at the application configuration file using the driver prefix before the parameter name.
+```
+   "target_overrides": {
+         ...
+         "NUCLEO_F429ZI": {
+             "spif-driver.SPI_MOSI": "PC_12",
+             "spif-driver.SPI_MISO": "PC_11",
+             "spif-driver.SPI_CLK":  "PC_10",
+             "spif-driver.SPI_CS":   "PA_15"
+         },
+         ...
+     }
+```
+or 
+```
+   "target_overrides": {
+         ...
+         "NUCLEO_F429ZI": {
+             "sd.SPI_MOSI": "PC_12",
+             "sd.SPI_MISO": "PC_11",
+             "sd.SPI_CLK":  "PC_10",
+             "sd.SPI_CS":   "PA_15"
+         },
+         ...
+     }
+```
+
+Mbed OS has several options for the block device:
+
+- **SPIFBlockDevice** - Block device driver for NOR-based SPI flash devices that
+  support SFDP. NOR-based SPI flash supports byte-sized read and writes, with an
+  erase size of about 4kbytes. An erase sets a block to all 1s, with successive
+  writes clearing set bits.
+
+  ``` cpp
+  SPIFBlockDevice bd(
+          MBED_CONF_SPIF_DRIVER_SPI_MOSI,
+          MBED_CONF_SPIF_DRIVER_SPI_MISO,
+          MBED_CONF_SPIF_DRIVER_SPI_CLK,
+          MBED_CONF_SPIF_DRIVER_SPI_CS);
+  ```
+
+  Starting mbed-os 5.10 the SPIFBlockDevice is a component under mbed-os. In order to add a component to the application use the following `target_overrides` configuration at the application configuration file:
+```
+  "target_overrides": {
+         ...
+         "NUCLEO_F429ZI": {
+             "target.components_add": ["SPIF"],
+             ...
+         },
+         ...
+  }
+```
+
+- **DataFlashBlockDevice** - Block device driver for NOR-based SPI flash devices
+  that support the DataFlash protocol, such as the Adesto AT45DB series of
+  devices. DataFlash is a memory protocol that combines flash with SRAM buffers
+  for a programming interface. DataFlash supports byte-sized read and writes, with
+  an erase size of about 528 bytes or sometimes 1056 bytes. DataFlash provides
+  erase sizes with an extra 16 bytes for error correction codes (ECC), so a flash
+  translation layer (FTL) may still present 512 byte erase sizes.
+  
+  ``` cpp
+  DataFlashBlockDevice bd(
+          MBED_CONF_DATAFLASH_SPI_MOSI,
+          MBED_CONF_DATAFLASH_SPI_MISO,
+          MBED_CONF_DATAFLASH_SPI_CLK,
+          MBED_CONF_DATAFLASH_SPI_CS);
+  ```
+
+  Starting mbed-os 5.10 the DataFlashBlockDevice is a component under mbed-os. In order to add a component to the application use the following `target_overrides` configuration at the application configuration file:
+```
+  "target_overrides": {
+         ...
+         "NUCLEO_F429ZI": {
+             "target.components_add": ["DATAFLASH"],
+             ...
+         },
+         ...
+  }
+```
+
+- **SDBlockDevice** - Block device driver for SD cards and eMMC memory chips. SD
+  cards or eMMC chips offer a full FTL layer on top of NAND flash. This makes the
+  storage well-suited for systems that require a about 1GB of memory.
+  Additionally, SD cards are a popular form of portable storage. They are useful
+  if you want to store data that you can access from a PC.
+  
+  ``` cpp
+  SDBlockDevice bd(
+          MBED_CONF_SD_SPI_MOSI,
+          MBED_CONF_SD_SPI_MISO,
+          MBED_CONF_SD_SPI_CLK,
+          MBED_CONF_SD_SPI_CS);
+  ```
+
+  Starting mbed-os 5.10 the SDBlockDevice is a component under mbed-os. In order to add a component to the application use the following `target_overrides` configuration at the application configuration file:
+```
+  "target_overrides": {
+         ...
+         "NUCLEO_F429ZI": {
+             "target.components_add": ["SD"],
+             ...
+         },
+         ...
+  }
+```
+
+- [**HeapBlockDevice**](https://os.mbed.com/docs/v5.6/reference/heapblockdevice.html) -
+  Block device that simulates storage in RAM using the heap. Do not use the heap
+  block device for storing data persistently because a power loss causes
+  complete loss of data. Instead, use it fortesting applications when a storage
+  device is not available.
+  
+  ``` cpp
+  HeapBlockDevice bd(1024*512, 512);
+  ```
+
+Additionally, Mbed OS contains several utility block devices to give you better
+control over the allocation of storage.
+
+- [**SlicingBlockDevice**](https://os.mbed.com/docs/latest/reference/slicingblockdevice.html) -
+  With the slicing block device, you can partition storage into smaller block
+  devices that you can use independently.
+
+- [**ChainingBlockDevice**](https://os.mbed.com/docs/latest/reference/chainingblockdevice.html) -
+  With the chaining block device, you can chain multiple block devices together
+  and extend the usable amount of storage.
+
+- [**MBRBlockDevice**](https://os.mbed.com/docs/latest/reference/mbrblockdevice.html) -
+  Mbed OS comes with support for storing partitions on disk with a Master Boot
+  Record (MBR). The MBRBlockDevice provides this functionality and supports
+  creating partitions at runtime or using preformatted partitions configured
+  separately from outside the application.
+
+- **ReadOnlyBlockDevice** - With the read-only block device, you can wrap a
+  block device in a read-only layer, ensuring that user of the block device does
+  not modify the storage.
+
+- **ProfilingBlockDevice** - With the profiling block device, you can profile
+  the quantity of erase, program and read operations that are incurred on a
+  block device.
+
+- **ObservingBlockDevice** - The observing block device grants the user the
+  ability to register a callback on block device operations. You can use this to
+  inspect the state of the block device, log different metrics or perform some
+  other operation.
+
+- **ExhaustibleBlockDevice** - Useful for evaluating how file systems respond to
+  wear, the exhaustible block device simulates wear on another form of storage.
+  You can configure it to expire blocks as necessary.
+
+## Tested configurations
+
+- K64F + Heap + LittleFS
+- K64F + Heap + FATFS
+- K64F + SD + LittleFS
+- K64F + SD + FATFS
+- K64F + SPIF (requires shield) + LittleFS
+- K64F + SPIF (requires shield) + FATFS
+- K64F + DataFlash (requires shield) + LittleFS
+- K64F + DataFlash (requires shield) + FATFS
+- UBLOX_EVK_ODIN_W2 \[1\] + Heap + LittleFS
+- UBLOX_EVK_ODIN_W2 \[1\] + Heap + FATFS
+- UBLOX_EVK_ODIN_W2 \[1\] + SD + LittleFS
+- UBLOX_EVK_ODIN_W2 \[1\] + SD + FATFS
+- UBLOX_EVK_ODIN_W2 \[1\] + SPIF (requires shield) + LittleFS
+- UBLOX_EVK_ODIN_W2 \[1\] + SPIF (requires shield) + FATFS
+- UBLOX_EVK_ODIN_W2 \[1\] + DataFlash (requires shield) + LittleFS
+- UBLOX_EVK_ODIN_W2 \[1\] + DataFlash (requires shield) + FATFS
+- NUCLEO_F429ZI + Heap + LittleFS
+- NUCLEO_F429ZI + Heap + FATFS
+- NUCLEO_F429ZI + SD (requires shield) + LittleFS
+- NUCLEO_F429ZI + SD (requires shield) + FATFS
+- NUCLEO_F429ZI + SPIF (requires shield) + LittleFS
+- NUCLEO_F429ZI + SPIF (requires shield) + FATFS
+- NUCLEO_F429ZI + DataFlash (requires shield) + LittleFS
+- NUCLEO_F429ZI + DataFlash (requires shield) + FATFS
+
+\[1\]: Note: The UBLOX_EVK_ODIN_W2 SPI pins conflict with the default serial
+pins. A different set of serial pins must be selected to use SPI flash with
+serial output.
+
+```c++
+// Connect Tx, Rx, and ground pins to a separte board running the passthrough example:
+// https://os.mbed.com/users/sarahmarshy/code/SerialPassthrough/file/2a3a62ee17fa/main.cpp/
+Serial pc(TX, RX);   
+
+pc.printf("...");    // Replace printf with pc.printf in the example
+```
+