fat12 | a simple fat12 filesystem | File Utils library

I am new to embedded development and have been tasked with implementing a file system on SPI flash memory. I am using a w25qxx chip and an STM32F4xx on STM32CubeIDE. I have successfully created the basic i/o for the w25 over SPI, being able to write and read sectors at a time.

In my user_diskio.c I have implemented all of the needed i/o methods and have verified that they are properly linked and being called.

in my main.cpp I go to format the drive using f_mkfs(), then get the free space, and finally open and close a file. However, f_mkfs() keeps returning FR_MKFS_ABORTED. (FF_MAX_SS is set to 16384)

I coded this small bootloader that prints a single character to the screen in 32-bit protected mode:

I am trying to develop a small OS with custom bootloader. I have a little bit of experience in OSDEV but not that much... My problem is that the first stage bootloader does not load the seconds from the disk. this is the boot.asm file:

I am writing a boot sector to load my 16-bit real mode DOS clone, and I'm stuck on something which might be completely obvious, but I've spent hours of time trying to understand why it won't work.

Basically, I'm trying to set DS, CS, SS to zero, but keep ES set directly past 7C00 to load the system.

But when running my code through a debugger, it says that nothing was ever read into memory, i.e.: root, FATs, etc (???)

Basically, I'm trying to compare DS:SI (0000:7C00+FILE) TO ES:DI (07E0:0000), but to no avail. I heard someone tell me that it actually checks DS:SI with DS:DI and so I tried it, but that didn't work either. Shouldn't 07E0:0000 be directly after 0000:7C00? Does cmpsb require ES & DS to be the same?

I've looked in the Intel manuals, but it says that cmpsb compares DS:SI to ES:DI, but I don't think I'm misunderstanding too much. 07E0:0000 is 0x7E00, no?

Anyway, thanks for any help. I appreciate it.

EDIT: I forgot to mention that if I zero ES and put the load address into BX, everything works. But when it's flipped, ES=07E0, BX=0, nothing works or is even read. No idea why, since ES:BX should be the same thing regardless of which route you take.

My code: