75 lines
2.9 KiB
Nim
75 lines
2.9 KiB
Nim
import serial
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type
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PageDirectoryEntry = uint32
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PageTableEntry = uint32
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PageDirectory = array[1024, PageDirectoryEntry]
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PageTable = array[1024, PageTableEntry]
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const
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blankPageDirectory: PageDirectoryEntry = 0x00000002
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var
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kernelMemoryStart{.importc: "_kernel_start"}: uint32
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kernelMemoryEnd{.importc: "_kernel_end"}: uint32
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proc kernelMemoryStartAddress(): uint32 = cast[uint32](kernelMemoryStart.addr)
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proc kernelMemoryEndAddress(): uint32 = cast[uint32](kernelMemoryEnd.addr)
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var
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pageDirectory: ptr PageDirectory
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pageTable0{.exportc, codegenDecl: "$# $# __attribute__((aligned(0x1000)))".}: PageTable
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proc createEntry(address: uint32, present: bool = false, readWrite: bool = false, userAccessible: bool = false, writeThrough: bool = false, disableCache: bool = false): uint32 =
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result = address and 0xFFFFF000'u32 # Set attributes section to zero
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if present: result = result or 0b1
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if readWrite: result = result or 0b10
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if userAccessible: result = result or 0b100
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if writeThrough: result = result or 0b1000
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if disableCache: result = result or 0b10000
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proc createDirectory(address: uint32, present: bool = false, readWrite: bool = false, userAccessible: bool = false, writeThrough: bool = false, disableCache: bool = false, pageSize: bool = false): uint32 =
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var checkAddress = address
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if pageSize: checkAddress = checkAddress and 0xFFFF0000'u32
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result = createEntry(address, present, readWrite, userAccessible, writeThrough, disableCache)
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if pageSize: result = result or 0b10000000
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proc loadPageDirectory(address: uint32){.inline.} =
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serial.writeLine("Loading paging data")
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asm """
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mov %%cr3, %%eax
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::"a"(`address`)
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"""
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# Converts a physical to a virtual address for the kernel
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proc toVirtual(address: uint32): uint32 =
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result = address + 0xC0000000'u32
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# Converts a physical to a virtual address for the kernel
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proc toPhysical(address: uint32): uint32 =
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result = address - 0xC0000000'u32
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# Each page starts from a multiple of 0x400000 769
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proc init*() =
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serial.writeLine("Initialising paging tables and directories.")
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var pagingAddress: uint32 = 0
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# Find the bootstrapped page directory
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asm """
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mov %%cr3, %%eax
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:"=a"(`pagingAddress`)
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"""
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pageDirectory = cast[ptr PageDirectory](toVirtual(pagingAddress))
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for i in 0..767:
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pageDirectory[][i] = blankPageDirectory
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var pages: uint = uint(int(kernelMemoryEndAddress() - 0xC0000000'u32) / 0x1000)
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serial.write("Pages:")
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serial.writeLine(pages)
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# Assign VGA memory area to 0xC0000000
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pageTable0[0] = createEntry(address = 0xB8000, readWrite = true, present = true)
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# Assign kernel memory pages to 0xC0100000+
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for i in 256..pages:
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pageTable0[i] = createEntry(address = uint32(i) * 0x1000, readWrite = true, present = true)
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pageDirectory[][768] = createDirectory(address = toPhysical(cast[uint32](pageTable0.addr)), readWrite = true, present = true)
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for i in 769..1023:
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pageDirectory[][i] = blankPageDirectory
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loadPageDirectory(pagingAddress) |