multiple changes: BL1/BL2/kernel separation (build system, etc.) BL2 implementation. BL documentation

bootloader/stage2.asm

@@ -0,0 +1,98 @@
+[BITS 32]
+global _start
+global ata_lba_read
+
+extern load_kernel
+
+_start:
+    ; Set up segments
+    ; Data segments
+    mov ax, 0x10
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+    mov ss, ax
+
+    ; Code segment
+    mov ax, 0x08
+    mov cs, ax
+
+    ; Stack (must be identity-mapped)
+    mov esp, 0x90000
+
+    call load_kernel
+
+    jmp eax
+
+; ----------------------------------------------------------------------------
+; ATA read sectors (LBA mode) 
+;
+; sysv32 abi signature:
+; void ata_lba_read(uint32_t lba, uint8_t nsect, void *addr);
+; ----------------------------------------------------------------------------
+ata_lba_read:
+    push ebp
+    mov ebp, esp
+
+    push ebx
+    push ecx
+    push edx
+    push edi
+
+    mov eax, [ebp+8]     ; arg #1 = LBA
+    mov cl, [ebp+12]     ; arg #2 = # of sectors
+    mov edi, [ebp+16]    ; arg #3 = buffer address
+    and eax, 0x0FFFFFFF
+
+    mov ebx, eax         ; Save LBA in RBX
+
+    mov edx, 0x01F6      ; Port to send drive and bit 24 - 27 of LBA
+    shr eax, 24          ; Get bit 24 - 27 in al
+    or al, 11100000b     ; Set bit 6 in al for LBA mode
+    out dx, al
+
+    mov edx, 0x01F2      ; Port to send number of sectors
+    mov al, cl           ; Get number of sectors from CL
+    out dx, al
+
+    mov edx, 0x1F3       ; Port to send bit 0 - 7 of LBA
+    mov eax, ebx         ; Get LBA from EBX
+    out dx, al
+
+    mov edx, 0x1F4       ; Port to send bit 8 - 15 of LBA
+    mov eax, ebx         ; Get LBA from EBX
+    shr eax, 8           ; Get bit 8 - 15 in AL
+    out dx, al
+
+    mov edx, 0x1F5       ; Port to send bit 16 - 23 of LBA
+    mov eax, ebx         ; Get LBA from EBX
+    shr eax, 16          ; Get bit 16 - 23 in AL
+    out dx, al
+
+    mov edx, 0x1F7       ; Command port
+    mov al, 0x20         ; Read with retry.
+    out dx, al
+
+    mov bl, cl          ; Save # of sectors in BL
+
+.wait_drq:
+    mov edx, 0x1F7
+.do_wait_drq:
+    in al, dx
+    test al, 8           ; the sector buffer requires servicing.
+    jz .do_wait_drq      ; keep polling until the sector buffer is ready.
+
+    mov edx, 0x1F0       ; Data port, in and out
+    mov ecx, 256
+    rep insw             ; in to [RDI]
+
+    dec bl               ; are we...
+    jnz .wait_drq        ; ...done?
+
+    pop edi
+    pop edx
+    pop ecx
+    pop ebx
+    pop ebp
+    ret