Visible to Intel only — GUID: suc1414435561397
Ixiasoft
Visible to Intel only — GUID: suc1414435561397
Ixiasoft
A.4.3.2. Boot Fuses
During boot ROM execution, the boot ROM reads user-programmed fuses that configure the boot state of the HPS.
- Clock select fuses: Determine the clock frequencies of the MPU clock, the interconnect clocks and the peripheral clocks.
- Debug fuses: Determine the state of debug during the boot process and during hand-off to the second-stage boot loader.
- RAM fuses: Determine whether or not the various peripheral RAMs are cleared during a warm reset and how they are cleared (series or parallel).
- Boot fuses: Determines whether the second-stage boot loader is from on-chip RAM, whether an internal or external clock is used for booting and whether the boot source is solely from FPGA.
- Security fuses: Determines whether the second-stage boot loader is authenticated or decrypted. If authentication is used, then there are fuses that are read by the boot ROM to determine where the key authorization key (KAK) resides and what its length is.
- User fuses: The user fuses may either hold proprietary user information or may hold the value of the KAK.
Bits |
Name | Description |
---|---|---|
31:27 | Reserved | Bit values in this field are undefined. |
26:23 | csel_f | This field indicates the value of the clock select fuses that are available for configuring the clock for the boot interface and for the PLLs. Refer to the Clock Configuration section for more information on CSEL encodings. |
22 | dbg_access_f | This fuse determines the initial state of the debug access domains. |
21 | dbg_lock_JTAG | This field indicates if the HPS JTAG access level can be changed through software when the HPS is released from reset.
|
20 | dbg_lock_DAP | This field indicates if the DAP access level can be changed through software when the HPS is released from reset.
|
19 | dbg_lock_CPU0 | This field indicates if the CPU0 debug access level can be changed through software when the HPS is released from reset.
|
18 | dbg_lock_CPU1 | This field indicates if the CPU1 debug access level can be changed through software when the HPS is released from reset.
|
17 | dbg_lock_CS | This field indicates if the CoreSight debug access level can be changed through software when the HPS is released from reset.
|
16 | dbg_lock_FPGA | This field indicates if the FPGA debug access level can be changed through software when the HPS is released from reset.
|
15:12 | Reserved | Bit values in this field are undefined. |
11 | clr_ram_order_f | This fuse value determines how RAMs are cleared during a tamper event.
|
10 | clr_ram_cold_f | This fuse value indicates what happens to the RAM on a cold reset.
|
9 | clr_ram_warm_f | This fuse value indicates what happens to the RAMs on a warm reset.
|
8 | oc_boot_f | This fuse value determines if the second-stage boot code is allowed to boot from on-chip RAM.
|
7 | hps_clk_f | This fuse value selects the clock used for the boot process and in the case of a tamper event, memory scrambling.
|
6 | fpga_boot_f | If blown, this fuse value allows the FPGA to configure independently and allows the HPS to boot from an encrypted next-stage boot source that was decrypted into the FPGA.
|
5 | aes_en_f | This fuse value indicates if a decryption of the flash image is always performed.
|
4:2 | kak_src_f | This bit field indicates the source of the Key Authorization Key (KAK) which can be in:
|
1 | kak_len_f | This fuse value indicates the Key Authorization Key (KAK) length:
|
0 | authen_en_f | This fuse value determines whether authentication of flash images is required prior to execution.
|
For more information about the fuses and how they work, refer to the SoC Security chapter.