119 lines
2.9 KiB
ArmAsm
119 lines
2.9 KiB
ArmAsm
/******************************************************************************
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* gpio.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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* gpio.s contains the rountines for manipulation of the GPIO ports.
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******************************************************************************/
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/* NEW
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* According to the EABI, all method calls should use r0-r3 for passing
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* parameters, should preserve registers r4-r8,r10-r11,sp between calls, and
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* should return values in r0 (and r1 if needed).
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* It does also stipulate many things about how methods should use the registers
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* and stack during calls, but we're using hand coded assembly. All we need to
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* do is obey the start and end conditions, and if all our methods do this, they
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* would all work from C.
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*/
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/* NEW
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* GetGpioAddress returns the base address of the GPIO region as a physical address
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* in register r0.
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* C++ Signature: void* GetGpioAddress()
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*/
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.globl GetGpioAddress
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GetGpioAddress:
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gpioAddr .req r0
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ldr gpioAddr,=0x20200000
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mov pc,lr
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.unreq gpioAddr
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/* NEW
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* SetGpioFunction sets the function of the GPIO register addressed by r0 to the
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* low 3 bits of r1.
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* C++ Signature: void SetGpioFunction(u32 gpioRegister, u32 function)
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*/
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.globl SetGpioFunction
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SetGpioFunction:
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pinNum .req r0
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pinFunc .req r1
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cmp pinNum,#53
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cmpls pinFunc,#7
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movhi pc,lr
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push {lr}
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mov r2,pinNum
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.unreq pinNum
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pinNum .req r2
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bl GetGpioAddress
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gpioAddr .req r0
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functionLoop$:
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cmp pinNum,#9
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subhi pinNum,#10
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addhi gpioAddr,#4
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bhi functionLoop$
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add pinNum, pinNum,lsl #1
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lsl pinFunc,pinNum
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mask .req r3
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mov mask,#7 /* r3 = 111 in binary */
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lsl mask,pinNum /* r3 = 11100..00 where the 111 is in the same position as the function in r1 */
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.unreq pinNum
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mvn mask,mask /* r3 = 11..1100011..11 where the 000 is in the same poisiont as the function in r1 */
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oldFunc .req r2
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ldr oldFunc,[gpioAddr] /* r2 = existing code */
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and oldFunc,mask /* r2 = existing code with bits for this pin all 0 */
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.unreq mask
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orr pinFunc,oldFunc /* r1 = existing code with correct bits set */
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.unreq oldFunc
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str pinFunc,[gpioAddr]
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.unreq pinFunc
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.unreq gpioAddr
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pop {pc}
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/* NEW
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* SetGpio sets the GPIO pin addressed by register r0 high if r1 != 0 and low
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* otherwise.
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* C++ Signature: void SetGpio(u32 gpioRegister, u32 value)
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*/
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.globl SetGpio
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SetGpio:
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pinNum .req r0
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pinVal .req r1
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cmp pinNum,#53
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movhi pc,lr
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push {lr}
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mov r2,pinNum
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.unreq pinNum
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pinNum .req r2
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bl GetGpioAddress
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gpioAddr .req r0
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pinBank .req r3
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lsr pinBank,pinNum,#5
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lsl pinBank,#2
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add gpioAddr,pinBank
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.unreq pinBank
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and pinNum,#31
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setBit .req r3
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mov setBit,#1
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lsl setBit,pinNum
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.unreq pinNum
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teq pinVal,#0
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.unreq pinVal
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streq setBit,[gpioAddr,#40]
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strne setBit,[gpioAddr,#28]
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.unreq setBit
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.unreq gpioAddr
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pop {pc}
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