secure_boot_rot.c

.global reset_vector
reset_vector:
    la sp, m_stack_ptr # sp for hart 0 (to be adjusted for other harts)
    csrr a0, mhartid # a0 <-- mhartid

    # 2. All but hart 0 wait for a signal via IPI. Hart 0 proceeds, and will wake other harts.
    bne a0, zero, .hart_non_zero # hart 0

    # 2. Erase DRAM (if applicable)
#ifdef ERASE_DRAM
    li t0, DRAM_BASE
    li t1, DRAM_SIZE
    add t1, t1, t0  # t1 <-- top of DRAM
.dram_erase_loop:
    sd x0, -8(t1)
    sd x0, -16(t1)
    sd x0, -24(t1)
    sd x0, -32(t1)
    sd x0, -40(t1)
    sd x0, -48(t1)
    sd x0, -56(t1)
    sd x0, -64(t1)
    addi t1, t1, -64
    blt t0, t1, .dram_erase_loop
#endif

    # 3. Ask host to load ELF into DRAM
    # request elf from host
    li t0, MEM_LOADER_BASE
    li t1, DRAM_BASE
    sw t1, 0(t0) # NOTE this may differ from system to system
    fence # make sure the requet goes out
    # wait for host to finish
.wait_on_elf:
    ld t1, 8(t0)
    bnez t1, .wait_on_elf

    # 4. Run bootloader C routines
    call rot_bootloader # performs steps 5,6,7,8 as described below
    
    # ... additional instructions shown in a later section

.hart_non_zero:
    # Adjust stack pointer for this hart
    li t0, M_STACK_SIZE
    mul t0, t0, a0    # offset = mhartid * M_STACK_SIZE
    sub sp, sp, t0    # sp -= offset
    # Enable IPI to wait on
    la t0, .rot_wake_on_ipi
    csrw mtvec, t0
    csrsi mie, 8
    csrsi mstatus, 8
    # Wait for an IPI from core 0
.wait_on_ipi:
    wfi
    j .wait_on_ipi
    # ---