# Getting started with the Mbed OS block device test

You can use the Mbed OS block device test to test existing and new block devices.

You can find more information about the Mbed OS block device 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)
2. [Usage](#usage)
   - [Compile the test](#compile-the-test)
   - [Run the test](#run-the-test)
3. [Changing the block device](#changing-the-block-device)
4. [Tested configurations](#tested-configurations)

## Hardware requirements

This test uses a block device as storage. This can be either an external block device (one of SPI flash, DataFlash or an SD card) or simulated on a heap block device on boards with enough RAM.

## Usage

#### Compile the test

Invoke `mbed test`, and specify the name of your platform and your favorite toolchain (`GCC_ARM`, `ARM`, `IAR`). For example, for the ARM Compiler 5:

```
mbed test -m K64F -t ARM -n mbed-os-features-storage-tests-blockdevice-general_block_device --compile
```

#### Run the test

Use `mbed test` again:

```
mbed test -m K64F -t ARM -n mbed-os-features-storage-tests-blockdevice-general_block_device --run -v
```
   
#### Troubleshooting

Please review the [documentation](https://os.mbed.com/docs/latest/tutorials/debugging.html) for suggestions about how to fix possible issues you may face.

## Changing the block device

In Mbed OS, a C++ class that inherits from the [BlockDevice](https://os.mbed.com/docs/latest/reference/storage.html#block-devices) interface represents each block device.

This test uses the default block device that the function `get_default_instance()` receives. [SystemStorage.cpp](https://github.com/ARMmbed/mbed-os/blob/master/features/storage/system_storage/SystemStorage.cpp#L35-L77) defines this as `MBED_WEAK`. If you would like to test a new block device, you have to override it.

First add the new block device .cpp and header files to the [blockdevice folder](https://github.com/ARMmbed/mbed-os/tree/master/features/storage/blockdevice). Then, implement `get_default_instance()` inside the test `main.cpp`.

For example, to test the HeapBlockDevice, add:

``` diff
+#define TEST_BLOCK_SIZE 128
+#define TEST_BLOCK_DEVICE_SIZE 32*TEST_BLOCK_SIZE

+BlockDevice *BlockDevice::get_default_instance()
+{
+    utest_printf("NEW test block device!!!\n");
+    static HeapBlockDevice default_bd(TEST_BLOCK_DEVICE_SIZE, TEST_BLOCK_SIZE);
+    return &default_bd;
+}
```

Now you can recompile and run.

## Tested configurations

- K64F + SD.
- K64F + Heap.
- K82F + SPIF.
- K82F + Heap.