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Dependencies: BLE_API mbed-dev-bin nRF51822
Fork of microbit-dal by
source/asm/CortexContextSwitch.s.gcc
- Committer:
- Jonathan Austin
- Date:
- 2016-04-07
- Revision:
- 1:8aa5cdb4ab67
File content as of revision 1:8aa5cdb4ab67:
@ 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