101 lines
2.4 KiB
ArmAsm
101 lines
2.4 KiB
ArmAsm
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/******************************************************************************
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* main.s
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* by Alex Chadwick
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*
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* A sample assembly code implementation of the ok05 operating system, that
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* flashes out a pattern using the wait routine from ok04.
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*
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* main.s contains the main operating system, and IVT code.
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******************************************************************************/
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/*
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* .globl is a directive to our assembler, that tells it to export this symbol
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* to the elf file. Convention dictates that the symbol _start is used for the
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* entry point, so this all has the net effect of setting the entry point here.
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* Ultimately, this is useless as the elf itself is not used in the final
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* result, and so the entry point really doesn't matter, but it aids clarity,
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* allows simulators to run the elf, and also stops us getting a linker warning
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* about having no entry point.
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*/
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.section .init
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.globl _start
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_start:
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/*
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* Branch to the actual main code.
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*/
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b main
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/*
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* This command tells the assembler to put this code with the rest.
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*/
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.section .text
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/*
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* main is what we shall call our main operating system method. It never
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* returns, and takes no parameters.
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* C++ Signature: void main(void)
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*/
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main:
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/*
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* Set the stack point to 0x8000.
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*/
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mov sp,#0x8000
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/*
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* Use our new SetGpioFunction function to set the function of GPIO port 16 (OK
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* LED) to 001 (binary)
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*/
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mov r0,#16
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mov r1,#1
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bl SetGpioFunction
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/* NEW
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* Load in the pattern to flash and also store our position in the flash
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* sequence.
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*/
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ptrn .req r4
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ldr ptrn,=pattern
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ldr ptrn,[ptrn]
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seq .req r5
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mov seq,#0
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loop$:
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/* NEW
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* Use our new SetGpio function to set GPIO 16 base on the current bit in the
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* pattern causing the LED to turn on if the pattern contains 0, and off if it
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* contains 1.
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*/
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mov r0,#16
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mov r1,#1
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lsl r1,seq
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and r1,ptrn
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bl SetGpio
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/* NEW
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* We wait for 0.25s using our wait method.
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*/
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ldr r0,=250000
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bl Wait
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/* NEW
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* Loop over this process forevermore, incrementing the sequence counter.
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* When it reaches 32, its bit pattern becomes 100000, and so anding it with
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* 11111 causes it to return to 0, but has no effect on all patterns less than
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* 32.
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*/
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add seq,#1
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and seq,#0b11111
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b loop$
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/* NEW
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* In the data section of the kernel image, store the pattern we wish to flash
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* on the LED.
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*/
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.section .data
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.align 2
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pattern:
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.int 0b11111111101010100010001000101010
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