armmbed / flashiap-driver

[experimental] Block device driver using the mbed OS FlashIAP API

Block Device driver build on top of FlashIAP API

Warning

This driver is EXPERIMENTAL and improper usage could kill your board's flash.

This driver should only be used on platforms where the FlashIAP implementation is using external flash or in conjunction with a filesystem with wear leveling, that can operate on a page size granularity.

Additional concerns:

• The BlockDevice API assumes a uniform erase size so the underlying flash must also have uniform sectors.
• The FlashIAP may freeze code execution for a long period of time while writing to flash. Not even high-priority irqs will be allowed to run, which may interrupt background processes.

Configuration

The driver must be configured with the starting address for the internal flash area reserved for the block device and it's size in bytes. In the application's mbed_app.json, add the following lines:

{
    "target_overrides": {
        "K64F": {
            "flashiap-block-device.base-address": "<internal flash address where the block device starts>",
            "flashiap-block-device.size": "<number of bytes allocated to the internal flash block device>"
        }
    }
}

Tested on

• Realtek RTL8195AM
• K64F

flashiap-driver's Issues

Confusing documentation

I am trying to see if it is possible to use an nRF52 board (actually a UBLOX NINA-B112) and its internal flash to store the BLE Keys for bonding on power reset. The documentation is a bit confusing/fuzzy. It states:

This driver should only be used on platforms where the FlashIAP implementation is using external flash or in conjunction with a filesystem with wear leveling, that can operate on a page size granularity.

First off, why does a platform require the FlashIAP implementation to use external flash? Doesn't this defeat the entire purpose of using In Application Programming to use the internal flash of the processor? I was under the impression from reading the documentation of FlashIAP, that it uses the internal flash to do reads and writes. So what does having external flash have anything to do with the FlashIAP?

Secondly, it states I need to use a filesystem with wear leveling that can operate on a page size granularity. I would need a FileSystem to mount the FlashIAPBLockDevice in order to use the internal security manager that is built in to store the BLE keys for you. If I used the LittleFileSystem wouldn't I get the wear leveling? Not sure about the page size granularity though.

My point is if I don't have external flash available on the NRF52, will I be able to use this FlashIAP driver with the LittleFileSystem in order to store bonded keys (to be used on resets) using the BLE Security Manager?