Understanding Layout of the ISP Image File: ISPBOOOT.BIN

This article provides insight into the partition layout of the ISP image file, ISPBOOOT.BIN, tailored for SP7350. The ISP (In-System Program) file plays a pivotal role as it houses essential images enabling SP7350 to initialize and write data to flash devices, including eMMC device, SPI-NAND flash, 8-bit NAND flash, and SPI-NOR flash.

When the SP7350 powers on, its internal ROM code initiates a search for the ISPBOOOT.BIN file. The search location is the root directory of the first or solo partition on the selected boot devices, with options including an SD card or a USB flash drive. Once found, the file is loaded, extracting the first-stage boot loader, X-Boot, and storing it in the internal SRAM.

The X-Boot image, situated at offset 0 within ISPBOOOT.BIN, has a maximum size of 192 KiB, with the actual size recorded in the X-Boot image header. Upon successful checksum verification, the system transitions to execute X-Boot.

X-Boot initializes and trains the SDRAM controller, preparing the DRAM for use. Subsequently, it loads the TF-A (Trusted Firmware-A) and OP-TEE (Open Portable Trusted Execution Environment) images from the fip (firmware image package) partition within ISPBOOOT.BIN, storing them in DRAM. Additionally, the U-Boot image is extracted from offset 0x30000 of ISPBOOOT.BIN and stored in DRAM. Upon successful checksum verification for all images, the system proceeds to execute TF-A, followed by OP-TEE, and finally U-Boot.

U-Boot autonomously executes scripts to program the flash devices.

The partition layout of ISPBOOOT.BIN is illustrated below, commencing with the X-Boot image (partition name: xboot0), followed by the U-Boot image (partition name: uboot0), and a header detailing the subsequent partitions.

Note actual size is the file size aligned to 1k boundary.

The following table explains details of each partition.

If ISPBOOOT.BIN is for programming SPI-NOR flash, isp_script_nand partition will be replaced with isp_script_nor partition, no isp_script_emmc partition.

Refer to the code below for the definition of partition_info in the file_header.

#define SIZE_FILE_NAME      (32)
struct partition_info_s {
	u08 file_name[SIZE_FILE_NAME];  // file name of source (basename only)
	u08 md5sum[36];
	u32 file_offset;                // offset in output file
	u64 file_size;                  // file size of the partition
	u32 partition_start_addr;       // partition's start address in NAND, there will be an offset added in U-Boot script ($isp_nand_addr_1st_part), less than 4GB is expected.
	u64 partition_size;             // reserved size for this partition, less than 4GB is expected.
	u32 flags;
	u32 emmc_partition_start;       // Unit: block
	u32 reserved[7];                // let size of this structure == SIZE_PARTITION_INFO_S
} __attribute__((packed));

Refer to the code below for the definition of file_header.

#define SIZE_PARTITION_INFO_S           (128)
#define SIZE_INIT_SCRIPT                (2048)
#define NUM_OF_PARTITION                (111)
struct file_header_s {
	u08 signature[32];
	u08 init_script[SIZE_INIT_SCRIPT];
	u32 flags;
	u08 reserved[SIZE_PARTITION_INFO_S - 36];
	struct partition_info_s partition_info[NUM_OF_PARTITION];
} __attribute__((packed));          // sizeof(this structure) == 16384

The signature string is “Pentagram_ISP_image".