A Hello World Kernel black background at the beginning of the third line down, y

Question

A Hello World Kernel

black background at the beginning of the third line down, you would have to do the following:

Compute the address relative to the beginning of video memory:

Since one line is 80 characters long, the beginning of the third line down would be 80*(3-1) = 160

Multiply that relative location by 2 bytes / character: 160*2 = 320

Convert that to hexadecimal (e.g., using a converter: http://www.binaryhexconverter.com/decimal-to-hex-converter): 320 = 0x140

Add that to the starting address of video memory (0xB8000) to get the memory address: 0xB8000+0x140 = 0xB8140

Write 0x41, the ASCII code for the letter ‘A’, to address 0xB8140.

Write the color white (0x0F) to address 0xB8141

Explanation / Answer

Since 16 bit C provides no built in mechanism for writing to memory, you are provided with an assembly file, kernel.asm. This file contains a function putInMemory, which writes a byte to memory. The function putInMemory can be called from your C program and takes three parameters:

To write 'A' to address 0xB8140, you should call:     putInMemory(0xB000, 0x8140, 'A');

To print out the letter A in white at the beginning of the third line of the screen, call:

    putInMemory(0xB000, 0x8140, 'A');
    putInMemory(0xB000, 0x8141, 0x7);

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