f3c7ac9696
Instead of using the bootsector to load a bootloader, just put the bootloader in the ROM and call it a day. It looks for a file on the SD card in the root directory named `kernel.bin` and loads it into memory. This is not a perfect solution, as the kernel will grow larger and the kernel load address will have to change. At this point I could add back the bootloader, but that is for later. Also the bootloader is just a copy of the kernel, so that can be trimmed down a lot.
55 lines
1.8 KiB
ArmAsm
55 lines
1.8 KiB
ArmAsm
; ---------------------------------------------------------------------------
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; crt0.s
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; ---------------------------------------------------------------------------
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;
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; Startup code for cc65 (Single Board Computer version)
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.export _init, _exit
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.import _main
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.export __STARTUP__ : absolute = 1 ; Mark as startup
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.import __SDRAM_START__, __SDRAM_SIZE__ ; Linker generated
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.import copydata, zerobss, initlib, donelib
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.include "zeropage.inc"
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; ---------------------------------------------------------------------------
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; Place the startup code in a special segment
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.segment "STARTUP"
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; ---------------------------------------------------------------------------
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; A little light 6502 housekeeping
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_init: LDX #$FF ; Initialize stack pointer to $01FF
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TXS
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CLD ; Clear decimal mode
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; ---------------------------------------------------------------------------
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; Set cc65 argument stack pointer
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LDA #<(__SDRAM_START__ + __SDRAM_SIZE__)
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STA sp
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LDA #>(__SDRAM_START__ + __SDRAM_SIZE__)
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STA sp+1
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; ---------------------------------------------------------------------------
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; Initialize memory storage
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JSR zerobss ; Clear BSS segment
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JSR copydata ; Initialize DATA segment
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JSR initlib ; Run constructors
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; ---------------------------------------------------------------------------
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; Call main()
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cli
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JSR _main
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jmp ($fffc)
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; ---------------------------------------------------------------------------
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; Back from main (this is also the _exit entry): force a software break
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_exit: JSR donelib ; Run destructors
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BRK
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