Mercurial > hg > CbC > CbC_xv6
comparison src/swtch.S @ 0:83c23a36980d
Init
| author | Tatsuki IHA <e125716@ie.u-ryukyu.ac.jp> |
|---|---|
| date | Fri, 26 May 2017 23:11:05 +0900 |
| parents | |
| children |
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| -1:000000000000 | 0:83c23a36980d |
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| 1 # Context switch | |
| 2 # | |
| 3 # void swtch(struct context **old, struct context *new); | |
| 4 # | |
| 5 # Save current register context in old | |
| 6 # and then load register context from new. | |
| 7 # The stack is as r4_svc-r12_svc, lr_svc, sp_usr, lr_usr, and pc_usr | |
| 8 .global swtch | |
| 9 | |
| 10 swtch: | |
| 11 STMFD r13!, {r4-r12, lr} // push svc r4-r12, lr to the stack | |
| 12 | |
| 13 # switch the stack | |
| 14 STR r13, [r0] // save current sp to the old PCB (**old) | |
| 15 MOV r13, r1 // load the next stack | |
| 16 | |
| 17 # load the new registers. pc_usr is not restored here because | |
| 18 # LDMFD^ will switch mode if pc_usr is loaded. We just simply | |
| 19 # pop it out as pc_usr is saved on the stack, and will be loaded | |
| 20 # when we return from kernel to user space (swi or interrupt return) | |
| 21 | |
| 22 LDMFD r13!, {r4-r12, lr} // pop svc r4-r12, lr | |
| 23 | |
| 24 # return to the caller | |
| 25 bx lr | |
| 26 |