Intel® Arria® 10 Hard Processor System Technical Reference Manual

ID 683711
Date 8/28/2023
Public
Document Table of Contents

14.4.10.3. Preserving Bad Block Markers

When flash device manufacturers test their devices at the time of manufacture, they mark any bad device blocks that are found. Each bad block is marked at specific, known offsets, typically at the base of the spare area. A bad block marker is any byte value other than 0xFF (the normal state of erased flash).

Bad block markers can be overwritten by the last sector data in a page when ECC is enabled. This happens because the NAND flash controller also uses the main area of a page to store ECC information, which causes the last sector to spill over into the spare area. It is necessary for the system to preserve the bad block information prior to writing data, to ensure the correct identification of bad blocks in the flash device.

You can configure the NAND flash controller to skip over a specified number of bytes when it writes the last sector in a page to the spare area. This option allows the flash controller to preserve bad block markers. To use this option, write the desired offset to the spare_area_skip_bytes register in the config group. For example, if the device page size is 2 KB, and the device manufacturer stores the bad block markers in the first two bytes in the spare area, set the spare_area_skip_bytes register to 2. When the flash controller writes the last sector of the page that overlaps with the spare area, it starts at offset 2 in the spare area, skipping the bad block marker at offset 0. A value of 0 (default) specifies that no bytes are skipped. The value of spare_area_skip_bytes must be an even number. For example, if the bad block marker is a single byte, set spare_area_skip_bytes to 2.

In main area transfer mode, the NAND flash controller does not skip the bad block marker. Instead, it overrides the bad block marker with the value programmed in the spare_area_marker register in the config group. This 8‑bit register is used in conjunction with the spare_area_skip_bytes register in the config group to determine which bytes in the spare area of a page should be written with a the new marker value. For example, to mark a block as good set the spare_area_marker register to 0xFF and set the spare_area_skip_bytes register to the number of bytes that the marker should be written to, starting from the base of the spare area.

In the spare area transfer mode, the NAND flash controller ignores the spare_area_skip_bytes and spare_area_marker registers. The flash controller transfers the data exactly as received from the host or device.

In the main+spare area transfer mode, the NAND flash controller starts writing the last sector in a page into the spare area, starting at the offset specified in the spare_area_skip_bytes register. However, the area containing the bad block identifier information is overwritten by the data the host writes into the page. The host writes both the data sectors and the bad block markers. The flash controller depends on the host software to set up the bad block markers properly before writing the data.

Figure 63. Bad Block MarkerThe following figure shows an example of how the NAND flash controller can skip over a bad block marker. In this example, the flash device has a 2‑KB page with a 64‑byte spare area. A 14‑byte sector ECC is shown, with 8 byte per sector correction.