39 lines
1.3 KiB
Nim
39 lines
1.3 KiB
Nim
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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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pageDirectory: PageDirectory
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pageTable: 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 loadPageDirectory(address: uint32){.asmNoStackFrame.} =
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asm """
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mov `address`, %cr3
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mov %cr0, %eax
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or $0x80000001, %eax
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mov %eax, %cr0
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"""
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proc init*() =
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serial.writeLine("Initialising paging tables and directories.")
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for i in 0..1023:
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pageDirectory[i] = blankPageDirectory
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for i in 0..1023:
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pageTable[i] = createEntry(address = uint32(i) * 0x1000, readWrite = true, present = true)
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pageDirectory[0] = createEntry(address = cast[uint32](pageTable), readWrite = true, present = true)
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loadPageDirectory(cast[uint32](pageDirectory.addr))
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