Dot Development - xDot Family

This article covers topics specific to the xDot family of modules including xDot, xDot-ES (Essentials), and xDot-AD (Advanced).

For serial firmware upgrade instructions for all xDot variants, see the Programming section in Dot Development. The Dot Upgrade Tool in the Dot-AT-Firmware repository supports all xDot variants and handles CRC and bootloader stripping automatically.

Enabling external storage on xDot

XDot requires an external storage device for FOTA. Space is allocated to store the received file, a backup copy of the application, and an upgrade result file.

Storage devices must meet the following criteria:

• Work with MBed OS DataFlashBlockDevice or SPIFBlockDevice classes
• Maximum 4KB sector erase size
• Maximum 512 byte page size
• SPIF type components must support Serial Flash Discoverable Parameters (SFDP)
• 512KB of free space.

These parts have been tested:

• Macronix MX25R8035
• Adesto AT45DB041E

The block device driver must be configured in mbed_app.json.

Example SPIF Block device configuration:

{
    ...

    "target_overrides": {
        ...

        "XDOT_L151CC": {
            ...

            "target.components_add": ["SPIF"],

            "spif-driver.SPI_MOSI": "SPI_MOSI",
            "spif-driver.SPI_MISO": "SPI_MISO",
            "spif-driver.SPI_CLK": "SPI_SCK",
            "spif-driver.SPI_CS": "SPI_NSS",

            "flash-record-store.file-enable": 1,
            "flash-record-store.ext-flash-page-size": 512,
            "flash-record-store.ext-flash-sector-size": 4096,
            "flash-record-store.ext-flash-erase-size": 4096
        }
    }
}

Example DATAFLASH block device configuration:

{
    ...

    "target_overrides": {
        ...

        "XDOT_L151CC": {
            ...

            "target.components_add": ["DATAFLASH"],

            "dataflash.SPI_MOSI": "SPI_MOSI",
            "dataflash.SPI_MISO": "SPI_MISO",
            "dataflash.SPI_CLK": "SPI_SCK",
            "dataflash.SPI_CS": "SPI_NSS",
            "dataflash.binary-size": 1,

            "flash-record-store.file-enable": 1,
            "flash-record-store.ext-flash-page-size": 512,
            "flash-record-store.ext-flash-sector-size": 4096,
            "flash-record-store.ext-flash-erase-size": 4096
        }
    }
}

The mDot instance must be initialized with a block device instance. The xDot bootloader expects file storage to be allocated at the end of the flash device.

Example for initializing an SPIF block device:

#include "mbed.h"
#include "mDot.h"

#include "SPIFBlockDevice.h"
// #include "DataFlashBlockDevice.h"

...


int main()
{
    ...

    mbed::BlockDevice* ext_bd = NULL;

    ext_bd = new SPIFBlockDevice();
    // ext_bd = new DataFlashBlockDevice();
    int ret = ext_bd->init();
    // Check for zero size because DataFlashBlockDevice doesn't
    // return an error if the chip is not present
    if (ret < 0 || (ext_bd->size() == 0)) {
        delete ext_bd;
        ext_bd = NULL;
    }

    mDot* dot = mDot::getInstance(&plan, ext_bd);

    if (ext_bd != NULL) {
        logInfo("External flash device detected, type: %s, size: 0x%08x",
            ext_bd->get_type(), (uint32_t)ext_bd->size());
    }

    ...
}