Lesson 18

17-video-scroll/Makefile

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-../14-checkpoint/Makefile

17-video-scroll/Makefile

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+C_SOURCES = $(wildcard kernel/*.c drivers/*.c)
+HEADERS = $(wildcard kernel/*.h drivers/*.h)
+# Nice syntax for file extension replacement
+OBJ = ${C_SOURCES:.c=.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 &
+	${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

17-video-scroll/boot

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-../14-checkpoint/boot/

17-video-scroll/drivers/ports.c

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-../../16-video-driver/drivers/ports.c

17-video-scroll/drivers/ports.c

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+/**
+ * Read a byte from the specified port
+ */
+unsigned char port_byte_in (unsigned short port) {
+    unsigned char result;
+    /* Inline assembler syntax
+     * !! Notice how the source and destination registers are switched from NASM !!
+     *
+     * '"=a" (result)'; set '=' the C variable '(result)' to the value of register e'a'x
+     * '"d" (port)': map the C variable '(port)' into e'd'x register
+     *
+     * Inputs and outputs are separated by colons
+     */
+    __asm__("in %%dx, %%al" : "=a" (result) : "d" (port));
+    return result;
+}
+
+void port_byte_out (unsigned short port, unsigned char data) {
+    /* Notice how here both registers are mapped to C variables and
+     * nothing is returned, thus, no equals '=' in the asm syntax 
+     * However we see a comma since there are two variables in the input area
+     * and none in the 'return' area
+     */
+    __asm__("out %%al, %%dx" : : "a" (data), "d" (port));
+}
+
+unsigned short port_word_in (unsigned short port) {
+    unsigned short result;
+    __asm__("in %%dx, %%ax" : "=a" (result) : "d" (port));
+    return result;
+}
+
+void port_word_out (unsigned short port, unsigned short data) {
+    __asm__("out %%ax, %%dx" : : "a" (data), "d" (port));
+}

17-video-scroll/drivers/ports.h

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-../../16-video-driver/drivers/ports.h

17-video-scroll/drivers/ports.h

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+unsigned char port_byte_in (unsigned short port);
+void port_byte_out (unsigned short port, unsigned char data);
+unsigned short port_word_in (unsigned short port);
+void port_word_out (unsigned short port, unsigned short data);

17-video-scroll/drivers/screen.h

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-../../16-video-driver/drivers/screen.h

17-video-scroll/drivers/screen.h

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+#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);