The SPI directory is a collection of image descriptor pointers that point to the beginning of the programming image. Each pointer uses four bytes. If the SPI flash memory device supports only the 3-byte addressing mode, the first three bytes are used.
For IAP recovery to choose image 0 on power-up, the programming image pointer next to the image 0 pointer must be null (empty slot), otherwise auto update is chosen. The following figure shows the SPI flash directory with the programming image descriptor pointers.
The SPI directory contains the start addresses of the programming images. The SPI directory occupies 1 KB memory from sector 0 of external SPI flash memory. For example, if the external SPI flash contains three images: golden image, update image, and IAP image, then these images are stored at memory with starting the addresses: 0x400, 0xA00000, and 0x1400000. If the Libero configurator is used to program SPI flash with programming images, then the Libero configurator takes care of the programming SPI directory automatically. If the user application programs the external SPI flash with programming images, then the application must write starting addresses of each image into SPI directory starting from SPI flash address 0, as shown in the following figure.
