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35 lines
1.4 KiB
Markdown
35 lines
1.4 KiB
Markdown
7 years ago
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Tutorial 02 - Multicore C
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=========================
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Now let's try something more complex, shall we? By complex I mean stop the CPU cures just like in the first tutorial,
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but this time stop one of them from C!
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Start
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-----
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Now we have to distinguish the cores. For that, we read the *mpidr_el1* system register. If it's not zero, we'll
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do the former infinite loop. If it's zero, then we'll call a C function. But for that, we need a proper stack, and a
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zerod out bss segment in memory before the call instruction. I've added some more code to the Assembly to do all of
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that. In case the C code returns (shouldn't), we also jump to the same infinite loop the other CPU cores running.
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Makefile
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--------
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It became a bit trickier. I've added commands for compiling C sources, but in a comform way. From now on, we
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can use the same Makefile for every tutorial, regardless of the number of C sources, and I won't discuss it any
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further.
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Linker script
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-------------
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Likewise, the linker script became more complex too, as C needs data and bss sections. I've also added a calculation
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for the bss size, so that we can refer to it from the Assembly without any further hassle.
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It is important to start the text segment with the Assembly code, because we set the stack right before it, hence
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the KEEP(). This way our load address is 0x80000, the same as `_start` label and stack top.
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Main
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----
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Finaly, our first C code. Just an empty loop, but still! :-)
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