Writing incorrect characters to framebuffer - c

Question

I have been following a tutorial called "The little book about OS development". I can write individual characters to the framebuffer, but not the next character. Here are the files:
kmain.c
#include "io.h"
#define FB_BLACK 0
#define FB_BLUE 1
#define FB_GREEN 2
#define FB_CYAN 3
#define FB_RED 4
#define FB_MAGENTA 5
#define FB_BROWN 6
#define FB_LIGHTGREY 7
#define FB_DARKGREY 8
#define FB_LIGHTBLUE 9
#define FB_LIGHTGREEN 10
#define FB_LIGHTCYAN 11
#define FB_LIGHTRED 12
#define FB_LIGHTMAGENTA 13
#define FB_LIGHTBROWN 14
#define FB_WHITE 15
#define FB_COMMAND_PORT 0x3D4
#define FB_DATA_PORT 0x3D5
#define FB_HIGH_BYTE_COMMAND 14
#define FB_LOW_BYTE_COMMAND 15
char *fb = (char*)0x000B8000;
void fb_move_cursor(unsigned short pos) {
outb(FB_COMMAND_PORT, FB_HIGH_BYTE_COMMAND);
outb(FB_DATA_PORT, ((pos >> 8) & 0x00FF));
outb(FB_COMMAND_PORT, FB_LOW_BYTE_COMMAND);
outb(FB_DATA_PORT, pos & 0x00FF);
}
void fb_write_cell(unsigned int i, char c, unsigned char fg, unsigned char bg)
{
fb[i] = c;
fb[i + 1] = ((fg & 0x0F) << 4) | (bg & 0x0F);
}
void kmain(void) {
fb_write_cell(0, 'H', FB_WHITE, FB_BLACK);
fb_move_cursor(2);
fb_write_cell(1, 'i', FB_WHITE, FB_BLACK);
}
io.h
#ifndef INCLUDE_IOH
#define INCLUDE_IOH
void outb(unsigned short port, unsigned char data);
#endif
io.s
global outb
global hang
;Sends a byte to an io port
; [esp + 8] data byte
; [esp + 4] the io port
outb:
mov al, [esp + 8]
mov dx, [esp + 4]
out dx, al
ret
hang:
jmp hang; so that program can hang
loader.s
global loader
MAGIC_NUMBER equ 0x1BADB002 ;Multiboot constant
FLAGS equ 0x0 ;Multiboot flags
CHKSUM equ -MAGIC_NUMBER ;Multiboot checksum. Valid if CHKSUM + FLAGS + MAGIC_NUMBER == 0
KERNEL_STACK_SIZE equ 4096
section .bss
align 4
kernel_stack:
resb KERNEL_STACK_SIZE
section .text
align 4
dd MAGIC_NUMBER
dd FLAGS
dd CHKSUM
loader:
mov esp,kernel_stack+KERNEL_STACK_SIZE
extern kmain
call kmain
hang:
jmp hang
link.ld
ENTRY(loader) /* the name of the entry label */
SECTIONS {
. = 0x00100000; /* the code should be loaded at 1 MB */
.text ALIGN (0x1000) : /* align at 4 KB */
{
*(.text) /* all text sections from all files */
}
.rodata ALIGN (0x1000) : /* align at 4 KB */
{
*(.rodata*) /* all read-only data sections from all files */
}
.data ALIGN (0x1000) : /* align at 4 KB */
{
*(.data) /* all data sections from all files */
}
.bss ALIGN (0x1000) : /* align at 4 KB */
{
*(COMMON) /* all COMMON sections from all files */
*(.bss) /* all bss sections from all files */
}
}
Makefile
OBJECTS = loader.o kmain.o io.o
CC = gcc
CFLAGS = -m32 -nostdlib -nostdinc -fno-builtin -fno-stack-protector \
-nostartfiles -nodefaultlibs -Wall -Wextra -Werror -c
LDFLAGS = -T link.ld -melf_i386
AS = nasm
ASFLAGS = -f elf
all: kernel.elf
kernel.elf: $(OBJECTS)
ld $(LDFLAGS) $(OBJECTS) -o kernel.elf
os.iso: kernel.elf
cp kernel.elf iso/boot/kernel.elf
genisoimage -R \
-b boot/grub/stage2_eltorito \
-no-emul-boot \
-boot-load-size 4 \
-A os \
-input-charset utf8 \
-quiet \
-boot-info-table \
-o os.iso \
iso
run: os.iso
bochs -f bochsrc.txt -q
%.o: %.c
$(CC) $(CFLAGS) $< -o $#
%.o: %.s
$(AS) $(ASFLAGS) $< -o $#
clean:
rm -rf *.o kernel.elf os.iso
You can download the folder the project is in here
I expect to see "Hi" in the upper left corner, but instead I see 2 weird characters: Printing the first character and moving the cursor works fine, but when I attempt to print the second character, it messes up.
Edit: I realized that the first character is an incorrectly colored H.

Answer 1

#Margaret Bloom's comment solved my issue. The issue was that a character is 16 bits, and I needed to increment I by 2, but I was increment it by 1, causing it to overlap like this:
Intended: char1Data char1Color char2Data char2Color
Problem: char1Data char2Data char2Color