bootsector print hello

02-boot-sector-interrupts/README.md

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-We will improve a bit on our infinite-loop boot sector and print
-something on the screen. We will raise an interrupt for this.
-
-

02-bootsector-print/README.md

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+*Concepts you may want to Google beforehand: interrupts, CPU
+registers*
+
+We will improve a bit on our infinite-loop boot sector and print
+something on the screen. We will raise an interrupt for this.
+
+On this example we are going to write each character of the "Hello"
+word into the register `al` (lower part of `ax`), the bytes `0x0e`
+into `ah` (the higher part of `ax`) and raise interrupt `0x10` which
+tells the machine to print on screen the contents of `ax`.
+
+`0x0e` on `ah` is necessary to indicate tty mode.
+
+We will set tty mode only once though in the real world we 
+cannot be sure that the contents of `ah` are constant. Some other
+process may run on the CPU while we are sleeping, not clean
+up properly and leave garbage data on `ah`.
+
+For this example we don't need to take care of that since we are
+the only thing running on the CPU.
+
+Our new boot sector looks like this:
+```nasm
+mov ah, 0x0e ; tty mode
+mov al, 'H'
+int 0x10
+mov al, 'e'
+int 0x10
+mov al, 'l'
+int 0x10
+int 0x10 ; 'l' is still on al, remember?
+mov al, 'o'
+int 0x10
+
+jmp $ ; jump to current address = infinite loop
+
+; padding and magic number
+times 510 - ($-$$) db 0
+dw 0xaa55 
+```
+
+You can examine the binary data with `xxd file.bin`
+
+Anyway, you know the drill:
+
+`nasm -fbin boot_sect_hello.asm -o boot_sect_hello.bin`
+
+`qemu boot_sect_hello.bin`
+
+Your boot sector will say 'Hello' and hang on an infinite loop

02-bootsector-print/boot_sect_hello.asm

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+mov ah, 0x0e ; tty mode
+mov al, 'H'
+int 0x10
+mov al, 'e'
+int 0x10
+mov al, 'l'
+int 0x10
+int 0x10 ; 'l' is still on al, remember?
+mov al, 'o'
+int 0x10
+
+jmp $ ; jump to current address = infinite loop
+
+; padding and magic number
+times 510 - ($-$$) db 0
+dw 0xaa55 

03-bootsector-memory/README.md

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+TBD
+
+Our new boot sector will refer to memory addresses and labels