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@ The MIT License (MIT)
@ Copyright (c) 2016 British Broadcasting Corporation.
@ This software is provided by Lancaster University by arrangement with the BBC.
@ Permission is hereby granted, free of charge, to any person obtaining a
@ copy of this software and associated documentation files (the "Software"),
@ to deal in the Software without restriction, including without limitation
@ the rights to use, copy, modify, merge, publish, distribute, sublicense,
@ and/or sell copies of the Software, and to permit persons to whom the
@ Software is furnished to do so, subject to the following conditions:
@ The above copyright notice and this permission notice shall be included in
@ all copies or substantial portions of the Software.
@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
@ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
@ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
@ THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
@ FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
@ DEALINGS IN THE SOFTWARE.
.syntax unified
.cpu cortex-m0
.thumb
.text
.align 2
@ Export our context switching subroutine as a C function for use in mbed
.global swap_context
.global save_context
.global save_register_context
.global restore_register_context
@ R0 Contains a pointer to the TCB of the fibre being scheduled out.
@ R1 Contains a pointer to the TCB of the fibre being scheduled in.
@ R2 Contains a pointer to the base of the stack of the fibre being scheduled out.
@ R3 Contains a pointer to the base of the stack of the fibre being scheduled in.
swap_context:
@ Write our core registers into the TCB
@ First, store the general registers
@ Skip this is we're given a NULL parameter for the TCB
CMP R0, #0
BEQ store_context_complete
STR R0, [R0,#0]
STR R1, [R0,#4]
STR R2, [R0,#8]
STR R3, [R0,#12]
STR R4, [R0,#16]
STR R5, [R0,#20]
STR R6, [R0,#24]
STR R7, [R0,#28]
@ Now the high general purpose registers
MOV R4, R8
STR R4, [R0,#32]
MOV R4, R9
STR R4, [R0,#36]
MOV R4, R10
STR R4, [R0,#40]
MOV R4, R11
STR R4, [R0,#44]
MOV R4, R12
STR R4, [R0,#48]
@ Now the Stack and Link Register.
@ As this context is only intended for use with a fiber scheduler,
@ we don't need the PC.
MOV R6, SP
STR R6, [R0,#52]
MOV R4, LR
STR R4, [R0,#56]
store_context_complete:
@ Finally, Copy the stack. We do this to reduce RAM footprint, as stack is usually very small at the point
@ of scheduling, but we need a lot of capacity for interrupt handling and other functions.
@ Skip this is we're given a NULL parameter for the stack.
CMP R2, #0
BEQ store_stack_complete
LDR R4, [R0,#60] @ Load R4 with the fiber's defined stack_base.
store_stack:
SUBS R4, #4
SUBS R2, #4
LDR R5, [R4]
STR R5, [R2]
CMP R4, R6
BNE store_stack
store_stack_complete:
@
@ Now page in the new context.
@ Update all registers except the PC. We can also safely ignore the STATUS register, as we're just a fiber scheduler.
@
LDR R4, [R1, #56]
MOV LR, R4
LDR R6, [R1, #52]
MOV SP, R6
@ Copy the stack in.
@ n.b. we do this after setting the SP to make comparisons easier.
@ Skip this is we're given a NULL parameter for the stack.
CMP R3, #0
BEQ restore_stack_complete
LDR R4, [R1,#60] @ Load R4 with the fiber's defined stack_base.
restore_stack:
SUBS R4, #4
SUBS R3, #4
LDR R5, [R3]
STR R5, [R4]
CMP R4, R6
BNE restore_stack
restore_stack_complete:
LDR R4, [R1, #48]
MOV R12, R4
LDR R4, [R1, #44]
MOV R11, R4
LDR R4, [R1, #40]
MOV R10, R4
LDR R4, [R1, #36]
MOV R9, R4
LDR R4, [R1, #32]
MOV R8, R4
LDR R7, [R1, #28]
LDR R6, [R1, #24]
LDR R5, [R1, #20]
LDR R4, [R1, #16]
LDR R3, [R1, #12]
LDR R2, [R1, #8]
LDR R0, [R1, #0]
LDR R1, [R1, #4]
@ Return to caller (scheduler).
BX LR
@ R0 Contains a pointer to the TCB of the fibre to snapshot
@ R1 Contains a pointer to the base of the stack of the fibre being snapshotted
save_context:
@ Write our core registers into the TCB
@ First, store the general registers
STR R0, [R0,#0]
STR R1, [R0,#4]
STR R2, [R0,#8]
STR R3, [R0,#12]
STR R4, [R0,#16]
STR R5, [R0,#20]
STR R6, [R0,#24]
STR R7, [R0,#28]
@ Now the high general purpose registers
MOV R4, R8
STR R4, [R0,#32]
MOV R4, R9
STR R4, [R0,#36]
MOV R4, R10
STR R4, [R0,#40]
MOV R4, R11
STR R4, [R0,#44]
MOV R4, R12
STR R4, [R0,#48]
@ Now the Stack and Link Register.
@ As this context is only intended for use with a fiber scheduler,
@ we don't need the PC.
MOV R6, SP
STR R6, [R0,#52]
MOV R4, LR
STR R4, [R0,#56]
@ Finally, Copy the stack. We do this to reduce RAM footprint, as stackis usually very small at the point
@ of sceduling, but we need a lot of capacity for interrupt handling and other functions.
LDR R4, [R0,#60] @ Load R4 with the fiber's defined stack_base.
store_stack1:
SUBS R4, #4
SUBS R1, #4
LDR R5, [R4]
STR R5, [R1]
CMP R4, R6
BNE store_stack1
@ Restore scratch registers.
LDR R7, [R0, #28]
LDR R6, [R0, #24]
LDR R5, [R0, #20]
LDR R4, [R0, #16]
@ Return to caller (scheduler).
BX LR
@ R0 Contains a pointer to the TCB of the fiber to snapshot
save_register_context:
@ Write our core registers into the TCB
@ First, store the general registers
STR R0, [R0,#0]
STR R1, [R0,#4]
STR R2, [R0,#8]
STR R3, [R0,#12]
STR R4, [R0,#16]
STR R5, [R0,#20]
STR R6, [R0,#24]
STR R7, [R0,#28]
@ Now the high general purpose registers
MOV R4, R8
STR R4, [R0,#32]
MOV R4, R9
STR R4, [R0,#36]
MOV R4, R10
STR R4, [R0,#40]
MOV R4, R11
STR R4, [R0,#44]
MOV R4, R12
STR R4, [R0,#48]
@ Now the Stack Pointer and Link Register.
@ As this context is only intended for use with a fiber scheduler,
@ we don't need the PC.
MOV R4, SP
STR R4, [R0,#52]
MOV R4, LR
STR R4, [R0,#56]
@ Restore scratch registers.
LDR R4, [R0, #16]
@ Return to caller (scheduler).
BX LR
restore_register_context:
@
@ Now page in the new context.
@ Update all registers except the PC. We can also safely ignore the STATUS register, as we're just a fiber scheduler.
@
LDR R4, [R0, #56]
MOV LR, R4
LDR R4, [R0, #52]
MOV SP, R4
@ High registers...
LDR R4, [R0, #48]
MOV R12, R4
LDR R4, [R0, #44]
MOV R11, R4
LDR R4, [R0, #40]
MOV R10, R4
LDR R4, [R0, #36]
MOV R9, R4
LDR R4, [R0, #32]
MOV R8, R4
@ Low registers...
LDR R7, [R0, #28]
LDR R6, [R0, #24]
LDR R5, [R0, #20]
LDR R4, [R0, #16]
LDR R3, [R0, #12]
LDR R2, [R0, #8]
LDR R0, [R0, #0]
LDR R1, [R0, #4]
@ Return to caller (normally the scheduler).
BX LR
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