Difference between revisions of "BCT"

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Revision as of 20:24, 22 August 2017

BCT (Boot Configuration Table) is a data structure present on Tegra based devices that supplies boot time configuration parameters.

The Switch's BCT is included in the firmware package titles (0100000000000819 and 010000000000081A) and is installed into eMMC storage's boot partition 0. A total of four BCT copies can be installed into the system: normal, normal backup, safe mode and safe mode backup.

During boot, the boot ROM parses the appropriate BCT from eMMC storage and stores a copy of it in IRAM at address 0x40000000.

Structure

Below is the BCT structure used by the Switch, which is a minimal variation of the Tegra 210 BCT format.

Offset Size Field Description
0x0000 0x210 bad_block_table Table containing information on bad blocks
0x0000: num_entries (0x200)
0x0004: virtual_block_size (0x0F)
0x0005: block_size (0x0E)
0x0006: bad_blocks
0x0206: reserved
0x0210 0x100 bct_key BCT RSA key modulus
0x0310 0x30 bct_signature BCT object signature
0x0310: hash (empty)
0x0320: rsa_pss_signature
0x0420 0x04 sec_provisioning_key_num_insecure Used for Factory Secure Provisioning. Always 0.
0x0424 0x20 sec_provisioning_key Used for Factory Secure Provisioning. Always empty.
0x0444 0xCC customer_data Data block available for the customer. Used in key generation.
0x0444: padding_0x0C
0x0450: keyblob_0xB0
0x0500: padding_0x08
0x0508 0x04 odm_data Legacy field. Unused.
0x050C 0x04 reserved0 Legacy field. Unused.
0x0510 0x10 random_aes_block Always empty.
0x0520 0x10 unique_chip_id Always empty.
0x0530 0x04 boot_data_version Set to 0x00210001.
0x0534 0x04 block_size_log2 Always 0x0E.
0x0538 0x04 page_size_log2 Always 0x09.
0x053C 0x04 partition_size Always 0x01000000.
0x0540 0x04 num_param_sets Number of device parameter sets. Always 0x01.
0x0544 0x04 dev_type Device type. Set to 0x04 (dev_type_sdmmc).
0x0548 0x40 dev_params Device parameters
 0x0548: sdmmc_clock_divider (0x09 == 24MHz)
 0x054C: sdmmc_data_width (0x02 == sdmmc_data_width_8bit)
0x0588 0x04 num_sdram_sets Number of SDRAM parameter sets. Set to 0?
0x058C 0x768 sdram_params0
0x0CF4 0x768 sdram_params1
0x145C 0x768 sdram_params2
0x1BC4 0x768 sdram_params3
0x232C 0x04 num_bootloaders Number of bootloaders installed. Always 0x02 (maximum is 0x04).
0x2330 0x12C bootloader0_info Configuration parameters for bootloader 0 (normal).
0x2330: version (variable)
0x2334: start_block (0x00000040)
0x2338: start_page (0x00000000)
0x233C: length (variable)
0x2340: load_addr (0x40010000)
0x2344: entry_point (0x40010020)
0x2348: attribute (0x00000000)
0x234C: bootloader0_hash (empty)
0x235C: bootloader0_rsa_pss_signature
0x245C 0x12C bootloader1_info Configuration parameters for bootloader 1 (safe mode).
0x245C: version (variable)
0x2460: start_block (0x00000050)
0x2464: start_page (0x00000000)
0x2468: length (variable)
0x246C: load_addr (0x40010000)
0x2470: entry_point (0x40010020)
0x2474: attribute (0x00000000)
0x2478: bootloader1_hash (empty)
0x2488: bootloader1_rsa_pss_signature
0x2588 0x258 reserved1 Reserved space for bootloaders 2 and 3 (currently unused).
0x27E0 0x04 enable_fail_back Always 0.
0x27E4 0x04 secure_debug_control Always 0.
0x27E8 0x04 sec_provisioning_key_num_secure Always 0.
0x27EC 0x04 unk0 Always 0x08?
0x27F0 0x10 reserved2 Empty.

IRAM

When copied to IRAM, the BCT has an additional header as follows.

Offset Size Field Description
0x00 0x50 bct_global_header Contains pointers to actual BCT data.
0x4C: bct_data_addr (address of the actual BCT)
0x50 0x18 bootloader0_header Unknown structure.
0x00: is_active (if set to 0x01, bootloader0 is used) 
0x68 0x18 bootloader1_header Unknown structure.
0x00: is_active (if set to 0x01, bootloader1 is used) 
0x80 0x18 bootloader2_header Unknown structure.
0x00: is_active (if set to 0x01, bootloader2 is used) 
0x98 0x18 bootloader3_header Unknown structure.
0x00: is_active (if set to 0x01, bootloader3 is used)