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lesson 21, keyboard input and shell

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Carlos 2015-03-20 19:20:44 +01:00
parent 5aaabf189d
commit e9d0d6c388
25 changed files with 1217 additions and 3 deletions
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1
20-interrupts-timer/Makefile
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../19-interrupts-irqs/Makefile

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20-interrupts-timer/Makefile Normal file
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C_SOURCES = $(wildcard kernel/*.c drivers/*.c cpu/*.c libc/*.c)
HEADERS = $(wildcard kernel/*.h drivers/*.h cpu/*.h libc/*.h)
# Nice syntax for file extension replacement
OBJ = ${C_SOURCES:.c=.o cpu/interrupt.o}
# Change this if your cross-compiler is somewhere else
CC = /usr/local/i386elfgcc/bin/i386-elf-gcc
GDB = /usr/local/i386elfgcc/bin/i386-elf-gdb
# -g: Use debugging symbols in gcc
CFLAGS = -g
# First rule is run by default
os-image.bin: boot/bootsect.bin kernel.bin
cat $^ > os-image.bin
# '--oformat binary' deletes all symbols as a collateral, so we don't need
# to 'strip' them manually on this case
kernel.bin: boot/kernel_entry.o ${OBJ}
i386-elf-ld -o $@ -Ttext 0x1000 $^ --oformat binary
# Used for debugging purposes
kernel.elf: boot/kernel_entry.o ${OBJ}
i386-elf-ld -o $@ -Ttext 0x1000 $^
run: os-image.bin
qemu-system-i386 -fda os-image.bin
# Open the connection to qemu and load our kernel-object file with symbols
debug: os-image.bin kernel.elf
qemu-system-i386 -s -fda os-image.bin -d guest_errors,int &
${GDB} -ex "target remote localhost:1234" -ex "symbol-file kernel.elf"
# Generic rules for wildcards
# To make an object, always compile from its .c
%.o: %.c ${HEADERS}
${CC} ${CFLAGS} -ffreestanding -c $< -o $@
%.o: %.asm
nasm $< -f elf -o $@
%.bin: %.asm
nasm $< -f bin -o $@
clean:
rm -rf *.bin *.dis *.o os-image.bin *.elf
rm -rf kernel/*.o boot/*.bin drivers/*.o boot/*.o cpu/*.o

3
20-interrupts-timer/drivers/screen.c
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#include "screen.h"
#include "ports.h"
#include "../kernel/util.h"
#include "../drivers/ports.h"
/* Declaration of private functions */
int get_cursor_offset();

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21-shell/Makefile Symbolic link
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../20-interrupts-timer/Makefile

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21-shell/README.md Normal file
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**Goal: Clean the code a bit and parse user input**
In this lesson we will do tho things. First, we will clean up the code a bit, so it is ready
for further lessons. During the previous ones I tried to put things in the most predictable places,
but it is also a good exercise to know when the code base is growing and adapt it to current
and further needs.
Code cleaning
-------------
First of all, we will quickly start to need more utility functions
for handling strings and so on. In a regular OS, this is called the C library,
or libc for short.
Right now we have a `utils.c` which we will split into `mem.c` and `string.c`, with their respective headers.
Second, we will create a new function `irq_install()` so that the kernel
only needs to perform one call to initialize all the IRQs. That function
is akin to `isr_install()` and placed on the same `irq.c`.
While we're here, we will disable the `kprint()` on `timer_callback()`
to avoid filling the screen with junk, now that we know that it works
properly.
There is not a clear distinction between `cpu/` and `drivers/`.
Keep in mind that I'm
creating this tutorial while following many others, and each of them
has a distinct folder structure. The only change we will do for now is to
move `drivers/ports.*` into `cpu/` since it is clearly cpu-dependent code.
`boot/` is also CPU-dependent code, but we will not mess with it until
we implement the boot sequence for a different machine.
Keyboard characters
-------------------
How to access the typed characters, then?
- When a key is pressed, the callback gets the ASCII code via a new
arrays which are defined at the beginning of `keyboard.c`
- The callback then appends that character to a buffer, `key_buffer`
- It is also printed on the screen
- When the OS wants to read user input, it calls `libc/io.c:readline()`
`keyboard.c` also parses backspace, by removing the last element
of the key buffer, and deleting it from the screen, by calling
`screen.c:kprint_backspace()`. For this we needed to modify a bit
`print_char()` to not advance the offset when printing a backspace
Responding to user input
------------------------
The keyboard callback checks for a newline, and then calls the kernel,
telling it that the user has input something. Out final libc function
is `strcmp()`, which compares two strings and returns 0 if they
are equal. If the user inputs "END", we halt the CPU.
This is the most basic shell ever, but you should be proud, because
we implemented it from scratch. Do you realize how cool this is?
If you want to, expand `kernel.c` to parse more stuff. In the future,
when we have a filesystem, we will allow the user to run some basic commands.

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21-shell/boot Symbolic link
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../20-interrupts-timer/boot

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21-shell/cpu/idt.c Normal file
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#include "idt.h"
void set_idt_gate(int n, u32 handler) {
idt[n].low_offset = low_16(handler);
idt[n].sel = KERNEL_CS;
idt[n].always0 = 0;
idt[n].flags = 0x8E;
idt[n].high_offset = high_16(handler);
}
void set_idt() {
idt_reg.base = (u32) &idt;
idt_reg.limit = IDT_ENTRIES * sizeof(idt_gate_t) - 1;
/* Don't make the mistake of loading &idt -- always load &idt_reg */
__asm__ __volatile__("lidtl (%0)" : : "r" (&idt_reg));
}

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21-shell/cpu/idt.h Normal file
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#ifndef IDT_H
#define IDT_H
#include "types.h"
/* Segment selectors */
#define KERNEL_CS 0x08
/* How every interrupt gate (handler) is defined */
typedef struct {
u16 low_offset; /* Lower 16 bits of handler function address */
u16 sel; /* Kernel segment selector */
u8 always0;
/* First byte
* Bit 7: "Interrupt is present"
* Bits 6-5: Privilege level of caller (0=kernel..3=user)
* Bit 4: Set to 0 for interrupt gates
* Bits 3-0: bits 1110 = decimal 14 = "32 bit interrupt gate" */
u8 flags;
u16 high_offset; /* Higher 16 bits of handler function address */
} __attribute__((packed)) idt_gate_t ;
/* A pointer to the array of interrupt handlers.
* Assembly instruction 'lidt' will read it */
typedef struct {
u16 limit;
u32 base;
} __attribute__((packed)) idt_register_t;
#define IDT_ENTRIES 256
idt_gate_t idt[IDT_ENTRIES];
idt_register_t idt_reg;
/* Functions implemented in idt.c */
void set_idt_gate(int n, u32 handler);
void set_idt();
#endif

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21-shell/cpu/interrupt.asm Normal file
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; Defined in isr.c
[extern isr_handler]
[extern irq_handler]
; Common ISR code
isr_common_stub:
; 1. Save CPU state
pusha ; Pushes edi,esi,ebp,esp,ebx,edx,ecx,eax
mov ax, ds ; Lower 16-bits of eax = ds.
push eax ; save the data segment descriptor
mov ax, 0x10 ; kernel data segment descriptor
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
; 2. Call C handler
call isr_handler
; 3. Restore state
pop eax
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
popa
add esp, 8 ; Cleans up the pushed error code and pushed ISR number
sti
iret ; pops 5 things at once: CS, EIP, EFLAGS, SS, and ESP
; Common IRQ code. Identical to ISR code except for the 'call'
; and the 'pop ebx'
irq_common_stub:
pusha
mov ax, ds
push eax
mov ax, 0x10
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
call irq_handler ; Different than the ISR code
pop ebx ; Different than the ISR code
mov ds, bx
mov es, bx
mov fs, bx
mov gs, bx
popa
add esp, 8
sti
iret
; We don't get information about which interrupt was caller
; when the handler is run, so we will need to have a different handler
; for every interrupt.
; Furthermore, some interrupts push an error code onto the stack but others
; don't, so we will push a dummy error code for those which don't, so that
; we have a consistent stack for all of them.
; First make the ISRs global
global isr0
global isr1
global isr2
global isr3
global isr4
global isr5
global isr6
global isr7
global isr8
global isr9
global isr10
global isr11
global isr12
global isr13
global isr14
global isr15
global isr16
global isr17
global isr18
global isr19
global isr20
global isr21
global isr22
global isr23
global isr24
global isr25
global isr26
global isr27
global isr28
global isr29
global isr30
global isr31
; IRQs
global irq0
global irq1
global irq2
global irq3
global irq4
global irq5
global irq6
global irq7
global irq8
global irq9
global irq10
global irq11
global irq12
global irq13
global irq14
global irq15
; 0: Divide By Zero Exception
isr0:
cli
push byte 0
push byte 0
jmp isr_common_stub
; 1: Debug Exception
isr1:
cli
push byte 0
push byte 1
jmp isr_common_stub
; 2: Non Maskable Interrupt Exception
isr2:
cli
push byte 0
push byte 2
jmp isr_common_stub
; 3: Int 3 Exception
isr3:
cli
push byte 0
push byte 3
jmp isr_common_stub
; 4: INTO Exception
isr4:
cli
push byte 0
push byte 4
jmp isr_common_stub
; 5: Out of Bounds Exception
isr5:
cli
push byte 0
push byte 5
jmp isr_common_stub
; 6: Invalid Opcode Exception
isr6:
cli
push byte 0
push byte 6
jmp isr_common_stub
; 7: Coprocessor Not Available Exception
isr7:
cli
push byte 0
push byte 7
jmp isr_common_stub
; 8: Double Fault Exception (With Error Code!)
isr8:
cli
push byte 8
jmp isr_common_stub
; 9: Coprocessor Segment Overrun Exception
isr9:
cli
push byte 0
push byte 9
jmp isr_common_stub
; 10: Bad TSS Exception (With Error Code!)
isr10:
cli
push byte 10
jmp isr_common_stub
; 11: Segment Not Present Exception (With Error Code!)
isr11:
cli
push byte 11
jmp isr_common_stub
; 12: Stack Fault Exception (With Error Code!)
isr12:
cli
push byte 12
jmp isr_common_stub
; 13: General Protection Fault Exception (With Error Code!)
isr13:
cli
push byte 13
jmp isr_common_stub
; 14: Page Fault Exception (With Error Code!)
isr14:
cli
push byte 14
jmp isr_common_stub
; 15: Reserved Exception
isr15:
cli
push byte 0
push byte 15
jmp isr_common_stub
; 16: Floating Point Exception
isr16:
cli
push byte 0
push byte 16
jmp isr_common_stub
; 17: Alignment Check Exception
isr17:
cli
push byte 0
push byte 17
jmp isr_common_stub
; 18: Machine Check Exception
isr18:
cli
push byte 0
push byte 18
jmp isr_common_stub
; 19: Reserved
isr19:
cli
push byte 0
push byte 19
jmp isr_common_stub
; 20: Reserved
isr20:
cli
push byte 0
push byte 20
jmp isr_common_stub
; 21: Reserved
isr21:
cli
push byte 0
push byte 21
jmp isr_common_stub
; 22: Reserved
isr22:
cli
push byte 0
push byte 22
jmp isr_common_stub
; 23: Reserved
isr23:
cli
push byte 0
push byte 23
jmp isr_common_stub
; 24: Reserved
isr24:
cli
push byte 0
push byte 24
jmp isr_common_stub
; 25: Reserved
isr25:
cli
push byte 0
push byte 25
jmp isr_common_stub
; 26: Reserved
isr26:
cli
push byte 0
push byte 26
jmp isr_common_stub
; 27: Reserved
isr27:
cli
push byte 0
push byte 27
jmp isr_common_stub
; 28: Reserved
isr28:
cli
push byte 0
push byte 28
jmp isr_common_stub
; 29: Reserved
isr29:
cli
push byte 0
push byte 29
jmp isr_common_stub
; 30: Reserved
isr30:
cli
push byte 0
push byte 30
jmp isr_common_stub
; 31: Reserved
isr31:
cli
push byte 0
push byte 31
jmp isr_common_stub
; IRQ handlers
irq0:
cli
push byte 0
push byte 32
jmp irq_common_stub
irq1:
cli
push byte 1
push byte 33
jmp irq_common_stub
irq2:
cli
push byte 2
push byte 34
jmp irq_common_stub
irq3:
cli
push byte 3
push byte 35
jmp irq_common_stub
irq4:
cli
push byte 4
push byte 36
jmp irq_common_stub
irq5:
cli
push byte 5
push byte 37
jmp irq_common_stub
irq6:
cli
push byte 6
push byte 38
jmp irq_common_stub
irq7:
cli
push byte 7
push byte 39
jmp irq_common_stub
irq8:
cli
push byte 8
push byte 40
jmp irq_common_stub
irq9:
cli
push byte 9
push byte 41
jmp irq_common_stub
irq10:
cli
push byte 10
push byte 42
jmp irq_common_stub
irq11:
cli
push byte 11
push byte 43
jmp irq_common_stub
irq12:
cli
push byte 12
push byte 44
jmp irq_common_stub
irq13:
cli
push byte 13
push byte 45
jmp irq_common_stub
irq14:
cli
push byte 14
push byte 46
jmp irq_common_stub
irq15:
cli
push byte 15
push byte 47
jmp irq_common_stub

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#include "isr.h"
#include "idt.h"
#include "../drivers/screen.h"
#include "../libc/string.h"
#include "ports.h"
isr_t interrupt_handlers[256];
/* Can't do this with a loop because we need the address
* of the function names */
void isr_install() {
set_idt_gate(0, (u32)isr0);
set_idt_gate(1, (u32)isr1);
set_idt_gate(2, (u32)isr2);
set_idt_gate(3, (u32)isr3);
set_idt_gate(4, (u32)isr4);
set_idt_gate(5, (u32)isr5);
set_idt_gate(6, (u32)isr6);
set_idt_gate(7, (u32)isr7);
set_idt_gate(8, (u32)isr8);
set_idt_gate(9, (u32)isr9);
set_idt_gate(10, (u32)isr10);
set_idt_gate(11, (u32)isr11);
set_idt_gate(12, (u32)isr12);
set_idt_gate(13, (u32)isr13);
set_idt_gate(14, (u32)isr14);
set_idt_gate(15, (u32)isr15);
set_idt_gate(16, (u32)isr16);
set_idt_gate(17, (u32)isr17);
set_idt_gate(18, (u32)isr18);
set_idt_gate(19, (u32)isr19);
set_idt_gate(20, (u32)isr20);
set_idt_gate(21, (u32)isr21);
set_idt_gate(22, (u32)isr22);
set_idt_gate(23, (u32)isr23);
set_idt_gate(24, (u32)isr24);
set_idt_gate(25, (u32)isr25);
set_idt_gate(26, (u32)isr26);
set_idt_gate(27, (u32)isr27);
set_idt_gate(28, (u32)isr28);
set_idt_gate(29, (u32)isr29);
set_idt_gate(30, (u32)isr30);
set_idt_gate(31, (u32)isr31);
// Remap the PIC
port_byte_out(0x20, 0x11);
port_byte_out(0xA0, 0x11);
port_byte_out(0x21, 0x20);
port_byte_out(0xA1, 0x28);
port_byte_out(0x21, 0x04);
port_byte_out(0xA1, 0x02);
port_byte_out(0x21, 0x01);
port_byte_out(0xA1, 0x01);
port_byte_out(0x21, 0x0);
port_byte_out(0xA1, 0x0);
// Install the IRQs
set_idt_gate(32, (u32)irq0);
set_idt_gate(33, (u32)irq1);
set_idt_gate(34, (u32)irq2);
set_idt_gate(35, (u32)irq3);
set_idt_gate(36, (u32)irq4);
set_idt_gate(37, (u32)irq5);
set_idt_gate(38, (u32)irq6);
set_idt_gate(39, (u32)irq7);
set_idt_gate(40, (u32)irq8);
set_idt_gate(41, (u32)irq9);
set_idt_gate(42, (u32)irq10);
set_idt_gate(43, (u32)irq11);
set_idt_gate(44, (u32)irq12);
set_idt_gate(45, (u32)irq13);
set_idt_gate(46, (u32)irq14);
set_idt_gate(47, (u32)irq15);
set_idt(); // Load with ASM
}
/* To print the message which defines every exception */
char *exception_messages[] = {
"Division By Zero",
"Debug",
"Non Maskable Interrupt",
"Breakpoint",
"Into Detected Overflow",
"Out of Bounds",
"Invalid Opcode",
"No Coprocessor",
"Double Fault",
"Coprocessor Segment Overrun",
"Bad TSS",
"Segment Not Present",
"Stack Fault",
"General Protection Fault",
"Page Fault",
"Unknown Interrupt",
"Coprocessor Fault",
"Alignment Check",
"Machine Check",
"Reserved",
"Reserved",
"Reserved",
"Reserved",
"Reserved",
"Reserved",
"Reserved",
"Reserved",
"Reserved",
"Reserved",
"Reserved",
"Reserved",
"Reserved"
};
void isr_handler(registers_t r) {
kprint("received interrupt: ");
char s[3];
int_to_ascii(r.int_no, s);
kprint(s);
kprint("\n");
kprint(exception_messages[r.int_no]);
kprint("\n");
}
void register_interrupt_handler(u8 n, isr_t handler) {
interrupt_handlers[n] = handler;
}
void irq_handler(registers_t r) {
/* After every interrupt we need to send an EOI to the PICs
* or they will not send another interrupt again */
if (r.int_no >= 40) port_byte_out(0xA0, 0x20); /* slave */
port_byte_out(0x20, 0x20); /* master */
/* Handle the interrupt in a more modular way */
if (interrupt_handlers[r.int_no] != 0) {
isr_t handler = interrupt_handlers[r.int_no];
handler(r);
}
}
void irq_install() {
/* Enable interruptions */
asm volatile("sti");
/* IRQ0: timer */
init_timer(50);
/* IRQ1: keyboard */
init_keyboard();
}

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#ifndef ISR_H
#define ISR_H
#include "types.h"
/* ISRs reserved for CPU exceptions */
extern void isr0();
extern void isr1();
extern void isr2();
extern void isr3();
extern void isr4();
extern void isr5();
extern void isr6();
extern void isr7();
extern void isr8();
extern void isr9();
extern void isr10();
extern void isr11();
extern void isr12();
extern void isr13();
extern void isr14();
extern void isr15();
extern void isr16();
extern void isr17();
extern void isr18();
extern void isr19();
extern void isr20();
extern void isr21();
extern void isr22();
extern void isr23();
extern void isr24();
extern void isr25();
extern void isr26();
extern void isr27();
extern void isr28();
extern void isr29();
extern void isr30();
extern void isr31();
/* IRQ definitions */
extern void irq0();
extern void irq1();
extern void irq2();
extern void irq3();
extern void irq4();
extern void irq5();
extern void irq6();
extern void irq7();
extern void irq8();
extern void irq9();
extern void irq10();
extern void irq11();
extern void irq12();
extern void irq13();
extern void irq14();
extern void irq15();
#define IRQ0 32
#define IRQ1 33
#define IRQ2 34
#define IRQ3 35
#define IRQ4 36
#define IRQ5 37
#define IRQ6 38
#define IRQ7 39
#define IRQ8 40
#define IRQ9 41
#define IRQ10 42
#define IRQ11 43
#define IRQ12 44
#define IRQ13 45
#define IRQ14 46
#define IRQ15 47
/* Struct which aggregates many registers */
typedef struct {
u32 ds; /* Data segment selector */
u32 edi, esi, ebp, esp, ebx, edx, ecx, eax; /* Pushed by pusha. */
u32 int_no, err_code; /* Interrupt number and error code (if applicable) */
u32 eip, cs, eflags, useresp, ss; /* Pushed by the processor automatically */
} registers_t;
void isr_install();
void isr_handler(registers_t r);
typedef void (*isr_t)(registers_t);
void register_interrupt_handler(u8 n, isr_t handler);
#endif

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21-shell/cpu/ports.c Symbolic link
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../../20-interrupts-timer/drivers/ports.c

1
21-shell/cpu/ports.h Symbolic link
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../../20-interrupts-timer/drivers/ports.h

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21-shell/cpu/timer.c Normal file
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#include "timer.h"
#include "isr.h"
u32 tick = 0;
static void timer_callback(registers_t regs) {
tick++;
}
void init_timer(u32 freq) {
/* Install the function we just wrote */
register_interrupt_handler(IRQ0, timer_callback);
/* Get the PIT value: hardware clock at 1193180 Hz */
u32 divisor = 1193180 / freq;
u8 low = (u8)(divisor & 0xFF);
u8 high = (u8)( (divisor >> 8) & 0xFF);
/* Send the command */
port_byte_out(0x43, 0x36); /* Command port */
port_byte_out(0x40, low);
port_byte_out(0x40, high);
}

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#ifndef TIMER_H
#define TIMER_H
#include "types.h"
void init_timer(u32 freq);
#endif

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#ifndef TYPES_H
#define TYPES_H
/* Instead of using 'chars' to allocate non-character bytes,
* we will use these new type with no semantic meaning */
typedef unsigned int u32;
typedef int s32;
typedef unsigned short u16;
typedef short s16;
typedef unsigned char u8;
typedef char s8;
#define low_16(address) (u16)((address) & 0xFFFF)
#define high_16(address) (u16)(((address) >> 16) & 0xFFFF)
#endif

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#include "keyboard.h"
#include "../cpu/ports.h"
#include "../cpu/isr.h"
#include "screen.h"
#include "../libc/string.h"
#include "../kernel/kernel.h"
#define BACKSPACE 0x0E
#define ENTER 0x1C
#define SC_MAX 57
const char *sc_name[] = { "ERROR", "Esc", "1", "2", "3", "4", "5", "6",
"7", "8", "9", "0", "-", "=", "Backspace", "Tab", "Q", "W", "E",
"R", "T", "Y", "U", "I", "O", "P", "[", "]", "Enter", "Lctrl",
"A", "S", "D", "F", "G", "H", "J", "K", "L", ";", "'", "`",
"LShift", "\\", "Z", "X", "C", "V", "B", "N", "M", ",", ".",
"/", "RShift", "Keypad *", "LAlt", "Spacebar"};
const char sc_ascii[] = { '?', '?', '1', '2', '3', '4', '5', '6',
'7', '8', '9', '0', '-', '=', '?', '?', 'Q', 'W', 'E', 'R', 'T', 'Y',
'U', 'I', 'O', 'P', '[', ']', '?', '?', 'A', 'S', 'D', 'F', 'G',
'H', 'J', 'K', 'L', ';', '\'', '`', '?', '\\', 'Z', 'X', 'C', 'V',
'B', 'N', 'M', ',', '.', '/', '?', '?', '?', ' '};
static void keyboard_callback(registers_t regs) {
/* The PIC leaves us the scancode in port 0x60 */
u8 scancode = port_byte_in(0x60);
if (scancode > SC_MAX) return;
if (scancode == BACKSPACE) {
backspace(key_buffer);
kprint_backspace();
} else if (scancode == ENTER) {
kprint("\n");
user_input(key_buffer);
key_buffer[0] = '\0';
} else {
char letter = sc_ascii[(int)scancode];
char str[2] = {letter, '\0'};
append(key_buffer, letter);
kprint(str);
}
}
void init_keyboard() {
register_interrupt_handler(IRQ1, keyboard_callback);
}

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21-shell/drivers/keyboard.h Normal file
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#include "../cpu/types.h"
static char key_buffer[256];
void init_keyboard();

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21-shell/drivers/screen.c Normal file
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#include "screen.h"
#include "../cpu/ports.h"
/* Declaration of private functions */
int get_cursor_offset();
void set_cursor_offset(int offset);
int print_char(char c, int col, int row, char attr);
int get_offset(int col, int row);
int get_offset_row(int offset);
int get_offset_col(int offset);
/**********************************************************
* Public Kernel API functions *
**********************************************************/
/**
* Print a message on the specified location
* If col, row, are negative, we will use the current offset
*/
void kprint_at(char *message, int col, int row) {
/* Set cursor if col/row are negative */
int offset;
if (col >= 0 && row >= 0)
offset = get_offset(col, row);
else {
offset = get_cursor_offset();
row = get_offset_row(offset);
col = get_offset_col(offset);
}
/* Loop through message and print it */
int i = 0;
while (message[i] != 0) {
offset = print_char(message[i++], col, row, WHITE_ON_BLACK);
/* Compute row/col for next iteration */
row = get_offset_row(offset);
col = get_offset_col(offset);
}
}
void kprint(char *message) {
kprint_at(message, -1, -1);
}
void kprint_backspace() {
int offset = get_cursor_offset()-2;
int row = get_offset_row(offset);
int col = get_offset_col(offset);
print_char(0x08, col, row, WHITE_ON_BLACK);
}
/**********************************************************
* Private kernel functions *
**********************************************************/
/**
* Innermost print function for our kernel, directly accesses the video memory
*
* If 'col' and 'row' are negative, we will print at current cursor location
* If 'attr' is zero it will use 'white on black' as default
* Returns the offset of the next character
* Sets the video cursor to the returned offset
*/
int print_char(char c, int col, int row, char attr) {
unsigned char *vidmem = (unsigned char*) VIDEO_ADDRESS;
if (!attr) attr = WHITE_ON_BLACK;
/* Error control: print a red 'E' if the coords aren't right */
if (col >= MAX_COLS || row >= MAX_ROWS) {
vidmem[2*(MAX_COLS)*(MAX_ROWS)-2] = 'E';
vidmem[2*(MAX_COLS)*(MAX_ROWS)-1] = RED_ON_WHITE;
return get_offset(col, row);
}
int offset;
if (col >= 0 && row >= 0) offset = get_offset(col, row);
else offset = get_cursor_offset();
if (c == '\n') {
row = get_offset_row(offset);
offset = get_offset(0, row+1);
} else if (c == 0x08) { /* Backspace */
vidmem[offset] = ' ';
vidmem[offset+1] = attr;
} else {
vidmem[offset] = c;
vidmem[offset+1] = attr;
offset += 2;
}
/* Check if the offset is over screen size and scroll */
if (offset >= MAX_ROWS * MAX_COLS * 2) {
int i;
for (i = 1; i < MAX_ROWS; i++)
memory_copy(get_offset(0, i) + VIDEO_ADDRESS,
get_offset(0, i-1) + VIDEO_ADDRESS,
MAX_COLS * 2);
/* Blank last line */
char *last_line = get_offset(0, MAX_ROWS-1) + VIDEO_ADDRESS;
for (i = 0; i < MAX_COLS * 2; i++) last_line[i] = 0;
offset -= 2 * MAX_COLS;
}
set_cursor_offset(offset);
return offset;
}
int get_cursor_offset() {
/* Use the VGA ports to get the current cursor position
* 1. Ask for high byte of the cursor offset (data 14)
* 2. Ask for low byte (data 15)
*/
port_byte_out(REG_SCREEN_CTRL, 14);
int offset = port_byte_in(REG_SCREEN_DATA) << 8; /* High byte: << 8 */
port_byte_out(REG_SCREEN_CTRL, 15);
offset += port_byte_in(REG_SCREEN_DATA);
return offset * 2; /* Position * size of character cell */
}
void set_cursor_offset(int offset) {
/* Similar to get_cursor_offset, but instead of reading we write data */
offset /= 2;
port_byte_out(REG_SCREEN_CTRL, 14);
port_byte_out(REG_SCREEN_DATA, (unsigned char)(offset >> 8));
port_byte_out(REG_SCREEN_CTRL, 15);
port_byte_out(REG_SCREEN_DATA, (unsigned char)(offset & 0xff));
}
void clear_screen() {
int screen_size = MAX_COLS * MAX_ROWS;
int i;
char *screen = VIDEO_ADDRESS;
for (i = 0; i < screen_size; i++) {
screen[i*2] = ' ';
screen[i*2+1] = WHITE_ON_BLACK;
}
set_cursor_offset(get_offset(0, 0));
}
int get_offset(int col, int row) { return 2 * (row * MAX_COLS + col); }
int get_offset_row(int offset) { return offset / (2 * MAX_COLS); }
int get_offset_col(int offset) { return (offset - (get_offset_row(offset)*2*MAX_COLS))/2; }

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#ifndef SCREEN_H
#define SCREEN_H
#define VIDEO_ADDRESS 0xb8000
#define MAX_ROWS 25
#define MAX_COLS 80
#define WHITE_ON_BLACK 0x0f
#define RED_ON_WHITE 0xf4
/* Screen i/o ports */
#define REG_SCREEN_CTRL 0x3d4
#define REG_SCREEN_DATA 0x3d5
/* Public kernel API */
void clear_screen();
void kprint_at(char *message, int col, int row);
void kprint(char *message);
void kprint_backspace();
#endif

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#include "../cpu/isr.h"
#include "../drivers/screen.h"
#include "kernel.h"
void main() {
isr_install();
irq_install();
kprint("Type something, it will go through the kernel\n"
"Type END to halt the CPU\n> ");
// Do we need an infinite loop here?
}
void user_input(char *input) {
if (strcmp(input, "END") == 0) {
kprint("Stopping the CPU. Bye!\n");
asm volatile("hlt");
}
kprint("You said: ");
kprint(input);
kprint("\n> ");
}

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#ifndef KERNEL_H
#define KERNEL_H
void user_input(char *input);
#endif

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21-shell/libc/mem.c Normal file
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#include "mem.h"
void memory_copy(char *source, char *dest, int nbytes) {
int i;
for (i = 0; i < nbytes; i++) {
*(dest + i) = *(source + i);
}
}
void memory_set(u8 *dest, u8 val, u32 len) {
u8 *temp = (u8 *)dest;
for ( ; len != 0; len--) *temp++ = val;
}

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#ifndef MEM_H
#define MEM_H
#include "../cpu/types.h"
void memory_copy(char *source, char *dest, int nbytes);
void memory_set(u8 *dest, u8 val, u32 len);
#endif

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21-shell/libc/string.c Normal file
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#include "string.h"
/**
* K&R implementation
*/
void int_to_ascii(int n, char str[]) {
int i, sign;
if ((sign = n) < 0) n = -n;
i = 0;
do {
str[i++] = n % 10 + '0';
} while ((n /= 10) > 0);
if (sign < 0) str[i++] = '-';
str[i] = '\0';
reverse(str);
}
/* K&R */
void reverse(char s[]) {
int c, i, j;
for (i = 0, j = strlen(s)-1; i < j; i++, j--) {
c = s[i];
s[i] = s[j];
s[j] = c;
}
}
/* K&R */
int strlen(char s[]) {
int i = 0;
while (s[i] != '\0') ++i;
return i;
}
void append(char s[], char n) {
int len = strlen(s);
s[len] = n;
s[len+1] = '\0';
}
void backspace(char s[]) {
int len = strlen(s);
s[len-1] = '\0';
}
/* K&R
* Returns <0 if s1<s2, 0 if s1==s2, >0 if s1>s2 */
int strcmp(char s1[], char s2[]) {
int i;
for (i = 0; s1[i] == s2[i]; i++) {
if (s1[i] == '\0') return 0;
}
return s1[i] - s2[i];
}

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#ifndef STRINGS_H
#define STRINGS_H
void int_to_ascii(int n, char str[]);
void reverse(char s[]);
int strlen(char s[]);
void append(char s[], char n);
int strcmp(char s1[], char s2[]);
#endif