2 * U-boot - i386 Startup Code
4 * Copyright (c) 2002 Omicron Ceti AB, Daniel Engström <denaiel@omicron.se>
6 * See file CREDITS for list of people who contributed to this
9 * This program is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU General Public License as
11 * published by the Free Software Foundation; either version 2 of
12 * the License, or (at your option) any later version.
14 * This program is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 * GNU General Public License for more details.
19 * You should have received a copy of the GNU General Public License
20 * along with this program; if not, write to the Free Software
21 * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
33 .type _start, @function
34 .globl _i386boot_start
37 * This is the fail safe 32-bit bootstrap entry point. The
38 * following code is not executed from a cold-reset (actually, a
39 * lot of it is, but from real-mode after cold reset. It is
40 * repeated here to put the board into a state as close to cold
46 /* Turn of cache (this might require a 486-class CPU) */
52 /* Tell 32-bit code it is being entered from an in-RAM copy */
55 /* This is the 32-bit cold-reset entry point */
57 movl $0x18,%eax /* Load our segement registes, the
58 * gdt have already been loaded by start16.S */
65 /* Clear the interupt vectors */
69 * Skip low-level board and memory initialization if not starting
70 * from cold-reset. This allows us to do a fail safe boot-strap
71 * into a new build of U-Boot from a known-good boot flash
77 /* We call a few functions in the board support package
78 * since we have no stack yet we'll have to use %ebp
79 * to store the return address */
81 /* Early platform init (setup gpio, etc ) */
82 mov $early_board_init_ret, %ebp
86 /* The __port80 entry-point should be usabe by now */
87 /* so we try to indicate progress */
89 movl $.progress0, %ebp
90 jmp show_boot_progress_asm
94 mov $mem_init_ret, %ebp
98 /* fetch memory size (into %eax) */
99 mov $get_mem_size_ret, %ebp
104 * We are now in 'Flat Protected Mode' and we know how much memory
105 * the board has. The (temporary) Global Descriptor Table is not
106 * in a 'Safe' place (it is either in Flash which can be erased or
107 * reprogrammed or in a fail-safe boot-strap image which could be
110 * Move the final gdt to a safe place (top of RAM) and load it.
111 * This is not a trivial excercise - the lgdt instruction does not
112 * have a register operand (memory only) and we may well be
113 * running from Flash, so self modifying code will not work here.
114 * To overcome this, we copy a stub into upper memory along with
118 /* Reduce upper memory limit by (Stub + GDT Pointer + GDT) */
119 subl $(end_gdt_setup - start_gdt_setup), %eax
121 /* Copy the GDT and Stub */
122 movl $start_gdt_setup, %esi
124 movl $(end_gdt_setup - start_gdt_setup), %ecx
129 /* write the lgdt 'parameter' */
130 subl $(jmp_instr - start_gdt_setup - 4), %ebp
132 movl $(gdt_ptr - start_gdt_setup), %ebx
136 /* write the gdt address into the pointer */
137 movl $(gdt_addr - start_gdt_setup), %ebp
139 movl $(gdt - start_gdt_setup), %ebx
143 /* Save the return address */
144 movl $load_gdt_ret, %ebp
146 /* Load the new (safe) Global Descriptor Table */
150 /* Check we have enough memory for stack */
151 movl $CONFIG_SYS_STACK_SIZE, %ecx
155 /* indicate (lack of) progress */
157 movl $.progress0a, %ebp
158 jmp show_boot_progress_asm
162 /* Set stack pointer to upper memory limit*/
165 /* indicate progress */
167 movl $.progress1, %ebp
168 jmp show_boot_progress_asm
178 cmpl $0x55aa55aa, %ebx
182 /* indicate (lack of) progress */
184 movl $.progress1a, %ebp
185 jmp show_boot_progress_asm
191 /* indicate progress */
193 movl $.progress2, %ebp
194 jmp show_boot_progress_asm
199 /* Get upper memory limit */
201 subl $CONFIG_SYS_STACK_SIZE, %ecx
203 /* Create a Stack Frame */
207 /* stack_limit parameter */
209 call board_init_f /* Enter, U-boot! */
211 /* indicate (lack of) progress */
213 movl $.progress4a, %ebp
214 jmp show_boot_progress_asm
233 .word 0x30 /* limit (48 bytes = 6 GDT entries) */
243 * 0x18 32bit data/stack
245 * 0x28 16bit data/stack
250 .word 0, 0, 0, 0 /* NULL */
251 .word 0, 0, 0, 0 /* unused */
253 .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */
254 .word 0 /* base address = 0 */
255 .word 0x9B00 /* code read/exec */
256 .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */
258 .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */
259 .word 0x0 /* base address = 0 */
260 .word 0x9300 /* data read/write */
261 .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */
263 .word 0xFFFF /* 64kb */
264 .word 0 /* base address = 0 */
265 .word 0x9b00 /* data read/write */
266 .word 0x0010 /* granularity = 1 (+5th nibble of limit) */
268 .word 0xFFFF /* 64kb */
269 .word 0 /* base address = 0 */
270 .word 0x9300 /* data read/write */
271 .word 0x0010 /* granularity = 1 (+5th nibble of limit) */