2 * This file is part of the coreboot project.
4 * Copyright (C) 2009-2010 coresystems GmbH
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; version 2 of the License.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
20 #define REALMODE_BASE 0x600
21 #define RELOCATED(x) (x - __realmode_code + REALMODE_BASE)
26 /* This is the intXX interrupt handler stub code. It gets copied
27 * to the IDT and to some fixed addresses in the F segment. Before
28 * the code can used, it gets patched up by the C function copying
29 * it: byte 3 (the $0 in movb $0, %al) is overwritten with the int#.
36 movb $0, %al /* This instruction gets modified */
37 ljmp $0, $__interrupt_handler_16bit
38 .globl __idt_handler_size
39 __idt_handler_size = ( . - __idt_handler)
42 /* In order to be independent of coreboot's position in RAM
43 * we relocate a part of the code to the low megabyte, so the
44 * CPU can use it in real-mode. This code lives at __realmode_code.
46 .globl __realmode_code
49 /* Realmode IDT pointer structure. */
51 __realmode_idt = RELOCATED(.)
52 .word 1023 /* 16 bit limit */
53 .long 0 /* 24 bit base */
56 /* Preserve old stack */
57 __stack = RELOCATED(.)
60 /* Register store for realmode_call and realmode_interrupt */
61 __registers = RELOCATED(.)
65 .long 0 /* 12 - EDX */
66 .long 0 /* 16 - ESI */
67 .long 0 /* 20 - EDI */
70 .globl __realmode_call
71 __realmode_call = RELOCATED(.)
72 /* save all registers to the stack */
75 /* Move the protected mode stack to a safe place */
79 /* This function is called with regparm=0 and we have
80 * to skip the 32 byte from pushal. Hence start at 36.
85 movw %ax, __lcall_instr + 1
86 andl $0xffff0000, %eax
88 movw %ax, __lcall_instr + 3
90 /* initial register values */
92 movl %eax, __registers + 0 /* eax */
94 movl %eax, __registers + 4 /* ebx */
96 movl %eax, __registers + 8 /* ecx */
98 movl %eax, __registers + 12 /* edx */
100 movl %eax, __registers + 16 /* esi */
102 movl %eax, __registers + 20 /* edi */
104 /* Activate the right segment descriptor real mode. */
105 ljmp $0x28, $RELOCATED(1f)
108 /* 16 bit code from here on... */
110 /* Load the segment registers w/ properly configured
111 * segment descriptors. They will retain these
112 * configurations (limits, writability, etc.) once
113 * protected mode is turned off.
122 /* Turn off protection */
127 /* Now really going into real mode */
128 ljmp $0, $RELOCATED(1f)
130 /* Setup a stack: Put the stack at the end of page zero.
131 * That way we can easily share it between real and
132 * protected, since the 16 bit ESP at segment 0 will
133 * work for any case. */
139 /* Load 16 bit IDT */
144 /* Set all segments to 0x0000, ds to 0x0040 */
151 /* initialize registers for option rom lcall */
152 movl __registers + 0, %eax
153 movl __registers + 4, %ebx
154 movl __registers + 8, %ecx
155 movl __registers + 12, %edx
156 movl __registers + 16, %esi
157 movl __registers + 20, %edi
159 /* ************************************ */
160 __lcall_instr = RELOCATED(.)
163 /* ************************************ */
165 /* If we got here, just about done.
166 * Need to get back to protected mode
172 /* Now that we are in protected mode
173 * jump to a 32 bit code segment.
175 data32 ljmp $0x10, $RELOCATED(1f)
185 /* restore proper idt */
192 // TODO return AX from OPROM call
195 .globl __realmode_interrupt
196 __realmode_interrupt = RELOCATED(.)
197 /* save all registers to the stack */
203 /* This function is called with regparm=0 and we have
204 * to skip the 32 byte from pushal. Hence start at 36.
207 /* prepare interrupt calling code */
209 movb %al, __intXX_instr + 1 /* intno */
211 /* initial register values */
213 movl %eax, __registers + 0 /* eax */
215 movl %eax, __registers + 4 /* ebx */
217 movl %eax, __registers + 8 /* ecx */
219 movl %eax, __registers + 12 /* edx */
221 movl %eax, __registers + 16 /* esi */
223 movl %eax, __registers + 20 /* edi */
225 /* This configures CS properly for real mode. */
226 ljmp $0x28, $RELOCATED(1f)
228 .code16 /* 16 bit code from here on... */
230 /* Load the segment registers w/ properly configured segment
231 * descriptors. They will retain these configurations (limits,
232 * writability, etc.) once protected mode is turned off.
241 /* Turn off protected mode */
246 /* Now really going into real mode */
247 data32 ljmp $0, $RELOCATED(1f)
250 /* put the stack at the end of page zero. That way we can easily
251 * share it between real mode and protected mode, because %esp and
252 * %ss:%sp point to the same memory.
260 /* Load 16-bit intXX IDT */
265 /* Set all segments to 0x0000 */
271 /* initialize registers for intXX call */
272 movl __registers + 0, %eax
273 movl __registers + 4, %ebx
274 movl __registers + 8, %ecx
275 movl __registers + 12, %edx
276 movl __registers + 16, %esi
277 movl __registers + 20, %edi
279 __intXX_instr = RELOCATED(.)
280 .byte 0xcd, 0x00 /* This becomes intXX */
282 /* Ok, the job is done, now go back to protected mode coreboot */
287 /* Now that we are in protected mode jump to a 32-bit code segment. */
288 data32 ljmp $0x10, $RELOCATED(1f)
298 /* restore coreboot's 32-bit IDT */
306 /* This is the 16-bit interrupt entry point called by the IDT stub code.
308 * Before this code code is called, %eax is pushed to the stack, and the
309 * interrupt number is loaded into %al. On return this function cleans up
313 __interrupt_handler_16bit = RELOCATED(.)
319 /* Clean up the interrupt number. We could have done this in the stub,
320 * but it would have cost 2 more bytes per stub entry.
323 pushl %eax /* ... and make it the first parameter */
325 /* Switch to protected mode */
330 /* ... and jump to a 32 bit code segment. */
331 data32 ljmp $0x10, $RELOCATED(1f)
343 /* Call the C interrupt handler */
344 movl $interrupt_handler, %eax
347 /* Now return to real mode ... */
348 ljmp $0x28, $RELOCATED(1f)
351 /* Load the segment registers with properly configured segment
352 * descriptors. They will retain these configurations (limits,
353 * writability, etc.) once protected mode is turned off.
362 /* Disable Protected Mode */
367 /* Now really going into real mode */
368 ljmp $0, $RELOCATED(1f)
370 /* Restore real-mode stack segment */
374 /* Restore 16 bit IDT */
379 /* Set up segment registers to segment 0x0000 */
386 /* Restore all registers, including those
387 * manipulated by the C handler
397 .globl __realmode_code_size
398 __realmode_code_size = (. - __realmode_code)