summaryrefslogtreecommitdiff
path: root/cpu/i386/start16.S
diff options
context:
space:
mode:
Diffstat (limited to 'cpu/i386/start16.S')
-rw-r--r--cpu/i386/start16.S112
1 files changed, 112 insertions, 0 deletions
diff --git a/cpu/i386/start16.S b/cpu/i386/start16.S
new file mode 100644
index 00000000000..590a5a6c9d7
--- /dev/null
+++ b/cpu/i386/start16.S
@@ -0,0 +1,112 @@
+/*
+ * U-boot - i386 Startup Code
+ *
+ * Copyright (c) 2002 Omicron Ceti AB, Daniel Engström <denaiel@omicron.se>
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+
+#define BOOT_SEG 0xffff0000 /* linear segment of boot code */
+#define a32 .byte 0x67;
+#define o32 .byte 0x66;
+
+.section .start16, "ax"
+.code16
+.globl start16
+start16:
+ /* First we let the BSP do some early initialization
+ * this code have to map the flash to its final position
+ */
+ mov $board_init16_ret, %bp
+ jmp board_init16
+board_init16_ret:
+
+ /* Turn of cache (this might require a 486-class CPU) */
+ movl %cr0, %eax
+ orl $060000000,%eax
+ movl %eax, %cr0
+ wbinvd
+
+ /* load the descriptor tables */
+o32 cs lidt idt_ptr
+o32 cs lgdt gdt_ptr
+
+
+ /* Now, we enter protected mode */
+ movl %cr0, %eax
+ orl $1,%eax
+ movl %eax, %cr0
+
+ /* Flush the prefetch queue */
+ jmp ff
+ff:
+
+ /* Finally jump to the 32bit initialization code */
+ movw $code32start, %ax
+ movw %ax,%bp
+o32 cs ljmp *(%bp)
+
+ /* 48-bit far pointer */
+code32start:
+ .long _start /* offset */
+ .word 0x10 /* segment */
+
+idt_ptr:
+ .word 0 /* limit */
+ .long 0 /* base */
+
+gdt_ptr:
+ .word 0x30 /* limit (48 bytes = 6 GDT entries) */
+ .long BOOT_SEG + gdt /* base */
+
+ /* The GDT table ...
+ *
+ * Selector Type
+ * 0x00 NULL
+ * 0x08 Unused
+ * 0x10 32bit code
+ * 0x18 32bit data/stack
+ * 0x20 16bit code
+ * 0x28 16bit data/stack
+ */
+
+gdt:
+ .word 0, 0, 0, 0 /* NULL */
+ .word 0, 0, 0, 0 /* unused */
+
+ .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */
+ .word 0 /* base address = 0 */
+ .word 0x9B00 /* code read/exec */
+ .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */
+
+ .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */
+ .word 0x0 /* base address = 0 */
+ .word 0x9300 /* data read/write */
+ .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */
+
+ .word 0xFFFF /* 64kb */
+ .word 0 /* base address = 0 */
+ .word 0x9b00 /* data read/write */
+ .word 0x0010 /* granularity = 1 (+5th nibble of limit) */
+
+ .word 0xFFFF /* 64kb */
+ .word 0 /* base address = 0 */
+ .word 0x9300 /* data read/write */
+ .word 0x0010 /* granularity = 1 (+5th nibble of limit) */