In addition to specifying the origin and length of a memory range within a GROUP, you can also use the VFILL specifier to as described in Section 9.6.10.3 to allow ECC data to be generated for areas of the input memory range that remain uninitialized.

The load image will have gaps between output sections, and how these bits are set depends on your device. Most devices count empty spaces as 1’s, but if your device counts empty space as 0’s, the result of the CRC will be different. Thus, if the CRC result does not line up, make sure that you specify the empty space byte with the VFILL parameter, as shown in the following example:

MEMORY
{
    GROUP
    {
        FLASH : origin = 0x0000, length = 0x1000,
                VFILL = 0x0 /* Fill gaps with zeroes */
    } crc(_table_name, CRC8_PRIME)
}

If no VFILL parameter is specified, it defaults to 0x1, which fills everything with ones. Remember to update every memory range that has a fill value other than 0x1 for CRCs.