63 lines
1.4 KiB
ArmAsm
63 lines
1.4 KiB
ArmAsm
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/******************************************************************************
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* systemTimer.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.
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* See main.s for details.
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*
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* systemTime.s contains the code that interacts with the system timer.
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******************************************************************************/
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/*
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* The system timer runs at 1MHz, and just counts always. Thus we can deduce
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* timings by measuring the difference between two readings.
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*/
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/*
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* GetSystemTimerBase returns the base address of the System Timer region as a
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* physical address in register r0.
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* C++ Signature: void* GetSystemTimerBase()
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*/
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.globl GetSystemTimerBase
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GetSystemTimerBase:
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ldr r0,=0x20003000
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mov pc,lr
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/*
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* GetTimeStamp gets the current timestamp of the system timer, and returns it
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* in registers r0 and r1, with r1 being the most significant 32 bits.
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* C++ Signature: u64 GetTimeStamp()
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*/
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.globl GetTimeStamp
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GetTimeStamp:
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push {lr}
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bl GetSystemTimerBase
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ldrd r0,r1,[r0,#4]
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pop {pc}
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/*
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* Wait waits at least a specified number of microseconds before returning.
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* The duration to wait is given in r0.
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* C++ Signature: void Wait(u32 delayInMicroSeconds)
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*/
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.globl Wait
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Wait:
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delay .req r2
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mov delay,r0
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push {lr}
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bl GetTimeStamp
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start .req r3
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mov start,r0
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loop$:
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bl GetTimeStamp
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elapsed .req r1
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sub elapsed,r0,start
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cmp elapsed,delay
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.unreq elapsed
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bls loop$
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.unreq delay
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.unreq start
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pop {pc}
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