Nightloader/i386/legacy-boot/src-asm/drivers/acpi/utility.asm

MAIN_BIOS_AREA_START equ 0xe0000

; Arguments:
;   [Furthest from EBP]
;     1.    Pointer to RSDT
;     0.    Pointer to driver area of 65536 bytes
;   [Nearest to EBP]
acpi_enumerate_tables:
.prolog:
    push        esi
    sub         esp,                    32
    mov         esi,                    esp

    mov         [esi + (32 - 4)],       eax
    mov         [esi + (32 - 8)],       ebx
    mov         [esi + (32 - 12)],      ecx
    mov         [esi + (32 - 16)],      edx
    mov         [esi + (32 - 20)],      edi

    ; ESI + 4: Number of RSDT entries
    ; ESI + 8: Start of RSDT's entries

.get_table_metrics:
    ; First, get the length of the full RSDT with header
    mov ebx, [ebp + 8]
    mov eax, [ebx + 4]

    ; Subtract the length of the RSDT's header to just get
    ; the length of all the table
    sub eax, 36

    ; Save the value for later, to get the start of the entries.
    mov edx, eax

    ; Divide through 4 to get the number of entries
    shr eax, 2
    mov [esi + 4], eax

    ; Save the table entries' start
    add edx, [ebp + 4]
    mov [esi + 4], edx

.initialize_enumeration_loop:
    xor ecx, ecx

.enumeration_loop:
    cmp ecx, [esi + 4]

    ; Calculate the address of the current entry
    mov eax, ecx
    shl eax, 2
    mov ebx, [esi + 8]
    add ebx, eax

    mov eax, [ebx]

    inc ecx
    jmp .enumeration_loop

.epilog:
    mov         edi,                    [esi + (32 - 20)]
    mov         edx,                    [esi + (32 - 16)]
    mov         ecx,                    [esi + (32 - 12)]
    mov         ebx,                    [esi + (32 - 8)]
    mov         eax,                    [esi + (32 - 4)]

    add         esp,                    32
    pop         esi

    ret



; Arguments:
;   -- None --
acpi_search_rsdt:
.prolog:
    push        esi
    sub         esp,                    8
    mov         esi,                    esp

    mov         [esi],                  dword 0
    mov         [esi + 4],              ecx

.search_loop_header:
    mov         ecx,                    MAIN_BIOS_AREA_START

.search_loop:
    push        ebp
    mov         ebp,                    esp
    push        ecx
    push        dword .signature
    push        dword 8
    call        mem_equal
    mov         esp,                    ebp
    pop         ebp

    cmp         ax,                     0
    jne         .resolve_rsdp

    add         ecx,                    16
    cmp         ecx,                    0x100000
    jb          .search_loop
    
    ; If no "RSD PTR "-signature could be found
    xor         ecx,                    ecx
    jmp .epilog

.resolve_rsdp:
    ; The 4-byte RSDT-pointer is at byte-offset 4 into the RSDP strucfture.
    mov         eax,                    ecx
    add         eax,                    4
    mov         eax,                    [eax]

.epilog:
    mov         ecx,                    [esi + 4]
    add         esp,                    8
    pop         esi

    ret

.signature:
    db "RSD PTR "