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Merged
IanSeyler merged 1 commit into from
May 11, 2026
Merged

Adjustment of ACPI changes from dev branch #105

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58 changes: 36 additions & 22 deletions src/init/acpi.asm
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Original file line number Diff line number Diff line change
Expand Up @@ -17,45 +17,59 @@ init_acpi:
je foundACPIfromUEFI ; If so, jump - otherwise fall thru for BIOS

; Find the ACPI RSDP Structure on a BIOS system
; It's supposed to be somewhere in the first MiB of memory but some systems don't adhere to that
mov esi, 0x00000007 ; Start looking for the Root System Description Pointer Structure
searchingforACPI:
sub esi, 0x7
lodsq ; Load a quad word from RSI and store in RAX, then increment RSI by 8
cmp rax, rbx ; Verify the Signature
; The RSDP is potentially located in 2 places:
; 1) Within the first 1 KiB of the EBDA (Extended BIOS Data Area; a 2 byte address to the start of it is located at 0x40E)
; 2) In the BIOS ROM memory region from 0x000E0000 to 0x000FFFFF
; The signature always starts on a 16 byte boundary.
; If the system does not adhere to the standard then this will fail.

; ; Check EBDA (first 1KB)
; mov rsi, [p_EBDA]
; mov ecx, 64 ; 0x400 / 16 = 64 iterations
;acpi_search_ebda:
; cmp qword [rsi], rbx ; Compare the Signature
; je foundACPI
; add esi, 16
; dec ecx
; jnz acpi_search_ebda

; Check BIOS ROM area (0xE0000–0xFFFFF)
mov esi, 0xE0000 ; Start of BIOS ROM
mov ecx, 8192 ; 0x20000 / 16 = 8192 iterations
acpi_search_rom:
cmp qword [rsi], rbx ; Compare the Signature
je foundACPI
cmp esi, 0xFFFFFFF8 ; Keep looking until we get here
ja noACPI ; ACPI tables couldn't be found, fail
jmp searchingforACPI
add esi, 16
dec ecx
jnz acpi_search_rom
jmp noACPI ; ACPI tables couldn't be found, fail

; Find the ACPI RSDP Structure on a UEFI system
foundACPIfromUEFI:
mov rsi, [0x400830] ; TODO This should be passed properly
lodsq ; Signature
mov rax, [rsi] ; Signature
cmp rax, rbx ; Verify the Signature
jne noACPI ; If it isn't a match then fail

; Parse the Root System Description Pointer (RSDP) Structure (5.2.5.3)
; 8 bytes - Signature
; 1 byte - Checksum
; 6 bytes - OEMID
; 1 byte - Revision
; 4 bytes - Address
foundACPI: ; Found a Pointer Structure, verify the checksum
push rsi ; Save the RSDP location - currently pointing to the checksum
push rbx
push rsi ; Save the RSDP location
xor ebx, ebx
mov ecx, 20 ; As per the spec only the first 20 bytes matter
sub esi, 8 ; Bytes 0 thru 19 must sum to zero
mov ecx, 20 ; As per the spec only the first 20 bytes matter for checksum
nextchecksum:
lodsb ; Get a byte
add bl, al ; Add it to the running total
dec cl
jnz nextchecksum ; 'dec' will set the zero flag
mov al, bl ; Save the value to AL before RBX gets popped
pop rbx
pop rsi ; Restore the RSDP location
cmp al, 0 ; Verify the checksum is zero
jne searchingforACPI ; Checksum didn't check out? Keep looking for a valid record

lodsb ; Checksum
lodsd ; OEMID (First 4 bytes)
lodsw ; OEMID (Last 2 bytes)
cmp bl, 0 ; Verify the checksum is zero
jne noACPI ; Checksum didn't check out? Keep looking for a valid record
add rsi, 15 ; Add offset to revision byte
lodsb ; Revision (0 is v1.0, 1 is v2.0, 2 is v3.0, etc)
cmp al, 0
je foundACPIv1 ; If AL is 0 then the system is using ACPI v1.0
Expand Down
18 changes: 9 additions & 9 deletions src/pure64.asm
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Original file line number Diff line number Diff line change
Expand Up @@ -117,9 +117,9 @@ bootmode:
stosw ; BitsPerPixel
%endif

; Clear memory for the Page Descriptor Entries (0x10000 - 0x5FFFF)
; Clear memory for the Page Descriptor Entries (0x210000 - 0x25FFFF)
mov edi, 0x00210000
mov ecx, 81920
mov ecx, 320 * 1024 / 4
rep stosd ; Write 320KiB

; Create the temporary Page Map Level 4 Entries (PML4E)
Expand Down Expand Up @@ -205,8 +205,8 @@ start64:

mov edi, 0x5000 ; Clear the info map and system variable memory
xor eax, eax
mov ecx, 960 ; 3840 bytes (Range is 0x5000 - 0x5EFF)
rep stosd ; Don't overwrite the UEFI/BIOS data at 0x5F00
mov ecx, 3840 / 8 ; 3840 bytes (Range is 0x5000 - 0x5EFF)
rep stosq ; Don't overwrite the 256-byte UEFI/BIOS data at 0x5F00

mov [p_BootMode], bl
mov [p_BootDisk], bh
Expand Down Expand Up @@ -300,15 +300,15 @@ msg_boot_done:
%endif

; Clear out the first 20KiB of memory. This will store the 64-bit IDT, GDT, PML4, PDP Low, and PDP High
mov ecx, 5120
xor eax, eax
mov edi, eax
rep stosd
mov edi, edi
mov ecx, 20 * 1024 / 8
rep stosq ; Write 20KiB

; Clear memory for the Page Descriptor Entries (0x10000 - 0x5FFFF)
mov edi, 0x00010000
mov ecx, 81920
rep stosd ; Write 320KiB
mov ecx, 320 * 1024 / 8
rep stosq ; Write 320KiB

; Copy the GDT to its final location in memory
mov esi, gdt64
Expand Down
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