![arnes boot record arnes boot record](https://i.pinimg.com/474x/10/59/3d/10593d34f4425a93ce1f1ddd1f1a51d3.jpg)
Far jump to second stage at 0x0000:0x7e00 SS:SP is already at 0x0000:0x7c00, keep it that way Xor ax, ax ES=FS=GS=0 (DS zeroed earlier) FAR JMP to the Stage2 entry point at physical address 0x07e00 Mov ax, STAGE2_RUN_SEG Set up the segments appropriate for Stage2 to run read_sector_loop If we haven't then read next sector disk_error If CF set then disk errorĪdd di, 512>4 Advance to next 512 byte segment (0x20*16=512)Ĭmp si, STAGE2_LBA_END Have we reached the last stage2 sector? Mov ax, 0x0201 Call function 0x02 of int 13h (read sectors) Mov es, di Set ES to current segment number to read into Mov bp, DISK_RETRIES Set disk retry countĬall lba_to_chs Convert current LBA to CHS chk_for_last_lba Check to see if we are last sector in stage2 Mov si, STAGE2_LBA_START SI = LBA that stage2 starts at Mov di, STAGE2_LOAD_SEG DI = Current segment to read into Read Stage2 1 sector at a time until stage2 is completely loaded Include a BPB (1.44MB floppy with FAT12) to be more compatible with USB floppy mediaĬld Set string instructions to use forward movement Logical Block Address(LBA) Stage2 ends atĭISK_RETRIES equ 3 Number of times to retry on disk error STAGE2_LBA_END equ STAGE2_LBA_START + NUM_STAGE2_SECTORS STAGE2_LBA_START equ 1 Logical Block Address(LBA) Stage2 starts on Run stage2 with segment of 0x0000 and offset of 0x7e00 OEMname: db "mkfs.fat" mkfs.fat is what OEMname mkdosfs uses
#Arnes boot record code
The bootloader code would look like this: Control would then be transferred to it via a FAR JMP to 0x0000:0x7e00. This image would be read from disk starting at LBA 1 (first sector after the bootloader) using BIOS function Int 13/ah=2. One can do this by writing a bootloader in NASM that includes a binary image of the assembled code you wish to test. What you are asking for is rather trivial. I have written such code as part of other answers but never had an opportunity to present a simple test harness that could be referenced from other Stackoverflow questions.
![arnes boot record arnes boot record](https://c8.alamy.com/comp/2CPEAPF/englands-shaun-wright-phillips-c-is-challenged-by-germanys-per-mertesacker-l-and-arne-fredrich-r-during-their-international-friendly-soccer-match-in-london-england-august-22-2007-reuterstoby-melville-britain-2CPEAPF.jpg)
How would I go about building such a reusable bootloader? A common boilerplate/template would allow other Stack Overflow users wishing to help to test the code with a limited amount of fuss. Programmers often struggle to create a Minimal, Complete, and Verifiable Example. This would also serve as a good starting point for asking questions on Stack Overflow that involve OS development.
![arnes boot record arnes boot record](https://orthoarizona.org/wp-content/uploads/2018/10/Infographic_AZBJ_Hikers_1_0.jpg)
So far, my code exceeds 512 bytes, which is too large to fit in a simple boot sector. I am working on writing my own operating system.