fb3c7e04c4
This includes both separate .md files, and documentation that was on the head of the .S source files. Retest everything as this was done, and fix a few easy things.
74 lines
2.5 KiB
ArmAsm
74 lines
2.5 KiB
ArmAsm
#include "common.h"
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BEGIN
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CLEAR
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STAGE2
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mov $output, %di
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call do_e820
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/* Debug aid. */
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PRINT_WORD_HEX <%bp>
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PRINT_NEWLINE
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mov %bp, %ax
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mov $0, %dx
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/* Each entry is 24 bytes wide. */
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mov $24, %cx
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mul %cx
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PRINT_BYTES $output, <%ax>
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hlt
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/*
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This was copy pasted from:
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http://wiki.osdev.org/Detecting_Memory_%28x86%29#Getting_an_E820_Memory_Map
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use the INT 0x15, eax= 0xE820 BIOS function to get a memory map
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inputs: es:di -> destination buffer for 24 byte entries
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outputs: bp = entry count, trashes all registers except esi
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*/
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do_e820:
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xorl %ebx,%ebx # ebx must be 0 to start
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xorw %bp,%bp # keep an entry count in bp
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movl $0x0534D4150,%edx # Place "SMAP" into edx
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movl $0xe820,%eax
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movl $1, %es:20(%di)
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movl $24,%ecx # ask for 24 bytes
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int $0x15
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jc do_e820.failed # carry set on first call means "unsupported function"
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movl $0x0534D4150,%edx # Some BIOSes apparently trash this register?
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cmpl %edx,%eax # on success, eax must have been reset to "SMAP"
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jne do_e820.failed
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testl %ebx,%ebx # ebx = 0 implies list is only 1 entry long (worthless)
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je do_e820.failed
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jmp do_e820.jmpin
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do_e820.e820lp:
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movl $0xe820,%eax # eax, ecx get trashed on every int 0x15 call
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movl $1, %es:20(%di)
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movl $24,%ecx # ask for 24 bytes again
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int $0x15
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jc do_e820.e820f # carry set means "end of list already reached"
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movl $0x0534D4150,%edx # repair potentially trashed register
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do_e820.jmpin:
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jcxz do_e820.skipent # skip any 0 length entries
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cmpb $20,%cl # got a 24 byte ACPI 3.X response?
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jbe do_e820.notext
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testb $1, %es:29(%di)
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je do_e820.skipent
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do_e820.notext:
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mov %ecx, %es:8(%di)
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or %ecx, %es:12(%di)
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jz do_e820.skipent # if length uint64_t is 0, skip entry
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incw %bp # got a good entry: ++count, move to next storage spot
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addw $24,%di
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do_e820.skipent:
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testl %ebx,%ebx # if ebx resets to 0, list is complete
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jne do_e820.e820lp
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do_e820.e820f:
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#movw %bp,mmap_ent # store the entry count
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clc # there is "jc" on end of list to this point, so the carry must be cleared
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ret
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do_e820.failed:
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stc # "function unsupported" error exit
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ret
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output:
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