Changes

Memory layout (edit)

Revision as of 17:22, 29 August 2016

510 bytes removed , 17:22, 29 August 2016

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==0xFF4XX000==

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Each [[KThread|thread]] is allocated a 0x1000-byte page in this region: the first page at 0xFF401000 is for the first created thread, 0xFF403000 for the second thread. This region is used to store the SVC-mode stack for the thread, and thread context data used for context switching. When the IRQ handler, prefetch/data abort handlers, and undefined instruction handler are entered where the SPSR-mode=user, these handlers then store LR+SPSR for the current mode on the SVC-mode stack, then these handlers switch to SVC-mode.

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Each [[KThread|thread]] is allocated a 0x1000-byte page in this region for the [[KThreadContext|thread context]]: the first page at 0xFF401000 is for the first created thread, 0xFF403000 for the second thread. This region is used to store the SVC-mode stack for the thread, and thread context data used for context switching. When the IRQ handler, prefetch/data abort handlers, and undefined instruction handler are entered where the SPSR-mode=user, these handlers then store LR+SPSR for the current mode on the SVC-mode stack, then these handlers switch to SVC-mode.

This page does not contain a dedicated block for storing R0-PC(etc). For user-mode, the user-mode regs are instead saved on the SVC-mode stack when IRQs such as timers for context switching are triggered.

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~~Structure of this page, relative to page_endaddr-0xC8:~~

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~~{| class="wikitable" border="1"~~

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|-

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~~! Offset~~

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~~! Size~~

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~~! Description~~

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|-

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~~| 0x0~~

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|

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~~| SVC-mode stack-top. The 0x10-byte SVC-access-control for this thread is also located here, which is checked by the SVC-handler.~~

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|-

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~~| 0x18~~

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~~| 0x28~~

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~~| SVC-mode saved registers, stored/loaded during context switches: R4-R9, SL, FP, SP, LR. After loading these registers, the context switch code will jump to the loaded LR.~~

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~~| 0xC0~~

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~~| 4~~

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~~| fpexc from vmrs, used during context switches with the above saved registers.~~

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|}

For NATIVE_FIRM the memory pages for this region are located in FCRAM, however for TWL_FIRM these are located in AXI WRAM. For TWL_FIRM v6704 the first thread's page for this region is located at physical address 0x1FF93000, the next one at 0x1FF92000, etc.

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