Unit PlatformARMv6

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OldStack	The address to save the stack pointer to for the current thread (Passed in r0)
NewThread	The address to restore the stack pointer from for the new thread (Passed in r1)
NewThread	The handle of the new thread to switch to (Passed in r2)
Note	At the point of the actual context switch (str sp / ldr sp) the thread stacks will look like this: (See: ARMv6ThreadSetupStack for additional information) (Base "Highest Address" of Stack) . . . . cpsr <- The current program status register value to load on return from the context switch lr/pc <- The address to return to from the context switch lr <- The lr value prior to the context switch r12 <- r11 <- r10 <- r9 <- r8 <- r7 <- r6 <- The value of these registers prior to the context switch r5 <- r4 <- r3 <- r2 <- r1 <- r0 <- d15 <- d14 <- d13 <- d12 <- d11 <- d10 <- d9 <- d8 <- The value of these floating point registers prior to the context switch d7 <- d6 <- d5 <- d4 <- d3 <- d2 <- d1 <- d0 <- fpscr <- The floating point FPSCR register fpexc <- The floating point FPEXC register (Current StackPointer points to here) . . . . (Top "Lowest Address" of Stack) This form of context switch uses r12 to save the cpsr value (and RFE to restore it). Because this context switch is called from a routine which will have saved the value of r12 (which is caller save in the ARM ABI) then we do not need to save the original value of r12. The context switch will be performed from SYS mode to SYS mode, the cpsr value will include the control bits (Mode and IRQ/FIQ state) but not the flags values. Again the ARM ABI does not require that the flags be saved by the callee and so the caller would have accounted for any needed flags before calling. If the thread to be resumed was interrupted by an IRQ or FIQ then the cpsr will also contain the flags etc as they were at the point of interrupt. We do not need to account for the state bits in the cpsr since all operations are performed in ARM mode at present. The main requirement of this routine is to ensure that the context record on the stack matches exactly that which is created on an interrupt and also that created by ThreadSetupStack for a new thread. If this is correct then the next context switch for any given thread can be either by a call to reschedule or by an interrupt. Equally a new thread can be first run from a context switch that resulted from either a call to reschedule or an interrupt. Note that this routine could use: pop (lr) pop (r12) msr cpsr_c, r12 mov pc, lr To return but that would mess up the value of r12, lr and the cpsr flags etc if the thread being resumed was interrupted by an IRQ, FIQ or SWI. The use of RFE here allows for exactly the same behaviour no matter which way the context record is saved and restored.

procedure ARMv6ContextSwitchIRQ(OldStack,NewStack:Pointer; NewThread:TThreadHandle); assembler; nostackframe;

Description: Perform a context switch from one thread to another as a result of an interrupt request (IRQ)

OldStack	The address to save the stack pointer to for the current thread (Passed in r0)
NewStack	The address to restore the stack pointer from for the new thread (Passed in r1)
NewThread	The handle of the new thread to switch to (Passed in r2)
Note	At the point of the actual context switch (str sp / ldr sp) the thread stacks will look like this: (See: ARMv6ThreadSetupStack for additional information) (Base "Highest Address" of Stack) . . . . cpsr <- The current program status register value to load on return from the context switch lr/pc <- The address to return to from the context switch lr <- The lr value prior to the context switch r12 <- r11 <- r10 <- r9 <- r8 <- r7 <- r6 <- The value of these registers prior to the context switch r5 <- r4 <- r3 <- r2 <- r1 <- r0 <- d15 <- d14 <- d13 <- d12 <- d11 <- d10 <- d9 <- d8 <- The value of these floating point registers prior to the context switch d7 <- d6 <- d5 <- d4 <- d3 <- d2 <- d1 <- d0 <- fpscr <- The floating point FPSCR register fpexc <- The floating point FPEXC register (Current StackPointer points to here) . . . . (Top "Lowest Address" of Stack) This form of context switch relies on the IRQ handler to save the necessary registers including the lr, cpsr and other general registers from the point at which the thread was interrupted. The thread to be resumed may have been saved by a previous IRQ or by a call to the standard context switch from SchedulerReschule or it may be a new thread to be run for the first time. All of these result in the same context record on the stack and therefore can be resumed the same way. The context switch will be performed by switching to SYS mode, exchanging the stack pointers and then returning to IRQ mode.

procedure ARMv6ContextSwitchFIQ(OldStack,NewStack:Pointer; NewThread:TThreadHandle); assembler; nostackframe;

Description: Perform a context switch from one thread to another as a result of a fast interrupt request (FIQ)

OldStack	The address to save the stack pointer to for the current thread (Passed in r0)
NewStack	The address to restore the stack pointer from for the new thread (Passed in r1)
NewThread	The handle of the new thread to switch to (Passed in r2)
Note	At the point of the actual context switch (str sp / ldr sp) the thread stacks will look like this: (See: ARMv6ThreadSetupStack for additional information) (Base "Highest Address" of Stack) . . . . cpsr <- The current program status register value to load on return from the context switch lr/pc <- The address to return to from the context switch lr <- The lr value prior to the context switch r12 <- r11 <- r10 <- r9 <- r8 <- r7 <- r6 <- The value of these registers prior to the context switch r5 <- r4 <- r3 <- r2 <- r1 <- r0 <- d15 <- d14 <- d13 <- d12 <- d11 <- d10 <- d9 <- d8 <- The value of these floating point registers prior to the context switch d7 <- d6 <- d5 <- d4 <- d3 <- d2 <- d1 <- d0 <- fpscr <- The floating point FPSCR register fpexc <- The floating point FPEXC register (Current StackPointer points to here) . . . . (Top "Lowest Address" of Stack) This form of context switch relies on the FIQ handler to save the necessary registers including the lr, cpsr and other general registers from the point at which the thread was interrupted. The thread to be resumed may have been saved by a previous FIQ or by a call to the standard context switch from SchedulerReschule or it may be a new thread to be run for the first time. All of these result in the same context record on the stack and therefore can be resumed the same way. The context switch will be performed by switching to SYS mode, exchanging the stack pointers and then returning to FIQ mode.

procedure ARMv6ContextSwitchSWI(OldStack,NewStack:Pointer; NewThread:TThreadHandle);

Description: Perform a context switch from one thread to another as a result of a software interrupt (SWI)

OldStack	The address to save the stack pointer to for the current thread (Passed in r0)
NewStack	The address to restore the stack pointer from for the new thread (Passed in r1)
NewThread	The handle of the new thread to switch to (Passed in r2)
Note	At the point of the actual context switch (str sp / ldr sp) the thread stacks will look like this: (See: ARMv6ThreadSetupStack for additional information) (Base "Highest Address" of Stack) . . . . cpsr <- The current program status register value to load on return from the context switch lr/pc <- The address to return to from the context switch lr <- The lr value prior to the context switch r12 <- r11 <- r10 <- r9 <- r8 <- r7 <- r6 <- The value of these registers prior to the context switch r5 <- r4 <- r3 <- r2 <- r1 <- r0 <- d15 <- d14 <- d13 <- d12 <- d11 <- d10 <- d9 <- d8 <- The value of these floating point registers prior to the context switch d7 <- d6 <- d5 <- d4 <- d3 <- d2 <- d1 <- d0 <- fpscr <- The floating point FPSCR register fpexc <- The floating point FPEXC register (Current StackPointer points to here) . . . . (Top "Lowest Address" of Stack) This form of context switch relies on the SWI handler to save the necessary registers including the lr, cpsr and other general registers from the point at which the thread was interrupted. The thread to be resumed may have been saved by a previous SWI or by a call to the standard context switch from SchedulerReschule or it may be a new thread to be run for the first time. All of these result in the same context record on the stack and therefore can be resumed the same way. The context switch will be performed by switching to SYS mode, exchanging the stack pointers and then returning to SWI (SVC) mode.

function ARMv6InterlockedOr(var Target:LongInt; Value:LongInt):LongInt; assembler; nostackframe;

Description: Perform an atomic OR operation using LDREX/STREX

Note	See page ??? of the ARM1176JZF-S Technical Reference Manual

function ARMv6InterlockedXor(var Target:LongInt; Value:LongInt):LongInt; assembler; nostackframe;

Description: Perform an atomic XOR operation using LDREX/STREX

Note	See page ??? of the ARM1176JZF-S Technical Reference Manual

function ARMv6InterlockedAnd(var Target:LongInt; Value:LongInt):LongInt; assembler; nostackframe;

Description: Perform an atomic AND operation using LDREX/STREX

Note	See page ??? of the ARM1176JZF-S Technical Reference Manual

function ARMv6InterlockedDecrement(var Target:LongInt):LongInt; assembler; nostackframe;

Description: Perform an atomic decrement operation using LDREX/STREX

Note	See page 8-6 of the ARM1176JZF-S Technical Reference Manual

function ARMv6InterlockedIncrement(var Target:LongInt):LongInt; assembler; nostackframe;

Description: Perform an atomic increment operation using LDREX/STREX

Note	See page 8-6 of the ARM1176JZF-S Technical Reference Manual

function ARMv6InterlockedExchange(var Target:LongInt; Source:LongInt):LongInt; assembler; nostackframe;

Description: Perform an atomic exchange operation using LDREX/STREX

Note	See page 8-6 of the ARM1176JZF-S Technical Reference Manual

function ARMv6InterlockedAddExchange(var Target:LongInt; Source:LongInt):LongInt; assembler; nostackframe;

Description: Perform an atomic add and exchange operation using LDREX/STREX

Note	See page 8-6 of the ARM1176JZF-S Technical Reference Manual

function ARMv6InterlockedCompareExchange(var Target:LongInt; Source,Compare:LongInt):LongInt; assembler; nostackframe;

Description: Perform an atomic compare and exchange operation using LDREX/STREX

Note	See page 8-6 of the ARM1176JZF-S Technical Reference Manual

function ARMv6PageTableGetEntry(Address:PtrUInt):TPageTableEntry;

Description: Get and Decode the entry in the Page Table that corresponds to the supplied virtual address

Note	None documented

function ARMv6PageTableSetEntry(const Entry:TPageTableEntry):LongWord;

Description: Encode and Set an entry in the Page Table that corresponds to the supplied virtual address

Note	None documented

function ARMv6VectorTableGetEntry(Number:LongWord):PtrUInt;

Description: Return the address of the specified vector table entry number

Note	None documented

function ARMv6VectorTableSetEntry(Number:LongWord; Address:PtrUInt):LongWord;

Description: Set the supplied address as the value of the specified vector table entry number

Note	None documented

function ARMv6FirstBitSet(Value:LongWord):LongWord; assembler; nostackframe;

Description: To be documented

Note	ARM arm states that CLZ is supported for ARMv5 and above

function ARMv6CountLeadingZeros(Value:LongWord):LongWord; assembler; nostackframe;

Description: Equivalent of the GCC Builtin function __builtin_clz

Note	ARM arm states that CLZ is supported for ARMv5 and above

ARMv6 thread functions

procedure ARMv6PrimaryInit; assembler; nostackframe;

Description: To be documented

Note	None documented

function ARMv6SpinLock(Spin:PSpinEntry):LongWord; assembler; nostackframe;

Description: Lock an existing Spin entry

Spin	Pointer to the Spin entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6SpinUnlock(Spin:PSpinEntry):LongWord; assembler; nostackframe;

Description: Unlock an existing Spin entry

Spin	Pointer to the Spin entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6SpinLockIRQ(Spin:PSpinEntry):LongWord; assembler; nostackframe;

Description: Lock an existing Spin entry, disable IRQ and save the previous IRQ state

Spin	Pointer to the Spin entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6SpinUnlockIRQ(Spin:PSpinEntry):LongWord; assembler; nostackframe;

Description: Unlock an existing Spin entry and restore the previous IRQ state

Spin	Pointer to the Spin entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6SpinLockFIQ(Spin:PSpinEntry):LongWord; assembler; nostackframe;

Description: Lock an existing Spin entry, disable FIQ and save the previous FIQ state

Spin	Pointer to the Spin entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6SpinUnlockFIQ(Spin:PSpinEntry):LongWord; assembler; nostackframe;

Description: Unlock an existing Spin entry and restore the previous FIQ state

Spin	Pointer to the Spin entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6SpinLockIRQFIQ(Spin:PSpinEntry):LongWord; assembler; nostackframe;

Description: Lock an existing Spin entry, disable IRQ and FIQ and save the previous IRQ/FIQ state

Spin	Pointer to the Spin entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6SpinUnlockIRQFIQ(Spin:PSpinEntry):LongWord; assembler; nostackframe;

Description: Unlock an existing Spin entry and restore the previous IRQ/FIQ state

Spin	Pointer to the Spin entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6SpinCheckIRQ(Spin:PSpinEntry):Boolean;

Description: To be documented

Return	True if the mask would enable IRQ on restore, False if it would not

function ARMv6SpinCheckFIQ(Spin:PSpinEntry):Boolean;

Description: To be documented

Return	True if the mask would enable FIQ on restore, False if it would not

function ARMv6SpinExchangeIRQ(Spin1,Spin2:PSpinEntry):LongWord;

Description: To be documented

Note	None documented

function ARMv6SpinExchangeFIQ(Spin1,Spin2:PSpinEntry):LongWord;

Description: To be documented

Note	None documented

function ARMv6MutexLock(Mutex:PMutexEntry):LongWord; assembler; nostackframe;

Description: Lock an existing Mutex entry

Mutex	Pointer to the Mutex entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6MutexUnlock(Mutex:PMutexEntry):LongWord; assembler; nostackframe;

Description: Unlock an existing Mutex entry

Mutex	Pointer to the Mutex entry to lock (Passed in R0)
Return	ERROR_SUCCESS if completed or another error code on failure (Returned in R0)

function ARMv6MutexTryLock(Mutex:PMutexEntry):LongWord; assembler; nostackframe;

Description: Try to lock an existing Mutex entry

Mutex	Pointer to the Mutex entry to try to lock (Passed in R0)
Return	ERROR_SUCCESS if completed, ERROR_LOCKED if already locked or another error code on failure (Returned in R0)

function ARMv6ThreadGetCurrent:TThreadHandle; assembler; nostackframe;

Description: Get the current thread id from the c13 (Thread and process ID) register of system control coprocessor CP15

Note	See page 3-129 of the ARM1176JZF-S Technical Reference Manual

function ARMv6ThreadSetCurrent(Thread:TThreadHandle):LongWord; assembler; nostackframe;

Description: To be documented

Note	Set the current thread id in the c13 (Thread and process ID) register of system control coprocessor CP15 See page 3-129 of the ARM1176JZF-S Technical Reference Manual

function ARMv6ThreadSetupStack(StackBase:Pointer; StartProc:TThreadStart; ReturnProc:TThreadEnd; Parameter:Pointer):Pointer;

Description: Set up the context record and arguments on the stack for a new thread

StackBase	Pointer to the base (highest address) of the allocated stack (as returned by ThreadAllocateStack
StartProc	The procedure the thread will start executing when resumed
ReturnProc	The procedure the thread will return to on exit
Return	Pointer to the starting address of the stack, which will be the Stack Pointer on the first context switch
Note	At the point of a context switch the thread stack will look like this: (Base "Highest Address" of Stack) . . . . cpsr <- The current program status register value to load on return from the context switch (On Interrupt: Includes the flags and control bits for the interrupted thread) (On Yield: Includes the control bits only for the yielded thread) (On Create: Includes the control bits only for the new thread) lr/pc <- The address to return to from the context switch (On Interrupt: The location the thread was at before interrupt) (On Yield: The location to return to in SchedulerReschedule) (On Create: The location of StartProc for the new thread) lr <- The lr value prior to the context switch (On Interrupt: The value of lr before the thread was interrupted) (On Yield: The location to return to in SchedulerReschedule) (On Create: The location of ReturnProc for the new thread) r12 <- r11 <- r10 <- r9 <- r8 <- r7 <- r6 <- The value of these registers prior to the context switch r5 <- (On Interrupt: The values before the thread was interrupted) r4 <- (On Yield: The values on return to SchedulerReschedule) r3 <- (On Create: The values on entry to StartProc as set by ThreadSetupStack) r2 <- r1 <- r0 <- d15 <- d14 <- d13 <- d12 <- d11 <- d10 <- d9 <- d8 <- The value of these floating point registers prior to the context switch d7 <- (On Interrupt: The values before the thread was interrupted) d6 <- (On Yield: The values on return to SchedulerReschedule) d5 <- (On Create: The values on entry to StartProc as set by ThreadSetupStack) d4 <- d3 <- d2 <- d1 <- d0 <- fpscr <- The floating point FPSCR register fpexc <- The floating point FPEXC register (Current StackPointer points to here) . . . . (Top "Lowest Address" of Stack) On exit from a standard context switch as performed by SchedulerReschedule the first value (Highest Address) of lr is used by the RFE (Return From Exception) instruction to load the pc which also loads the saved cpsr value. On exit from an IRQ or FIQ context switch as performed by SchedulerSwitch the first value (Highest Address) of lr is used by the interrupt handler to return from the interrupt. A standard context switch uses r12 to save the cpsr value (and RFE to restore it). Because the standard context switch is called from a routine which will have saved the value of r12 (which is caller save in the ARM ABI) then we do not need to save the original value of r12. An IRQ or FIQ context switch uses the SRS (Store Return State) and RFE (Return From Exception) instructions to save and restore the cpsr value from the spsr value of either IRQ or FIQ mode.

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Unit PlatformARMv6

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