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Re: TS 7200 kernel image size

On May 5, 2009, at 2:06 AM, Lloyd Parkes wrote:

I$ seems to be on, although it sure feels like it's off when using a gzimg. Maybe the RedBoot go command switches it off (unlikely), or the gzimg switches it off so that it doesn't have to manage it (more likely)?

One might say that I was taking the easy way out when I wrote gzboot. See sys/arch/evbarm/stand/gzboot/srtbegin.S:

         * We assume we've been loaded VA==PA, or that the MMU
         * is disabled.  Make sure the MMU is disabled so that
         * we don't have to care about the caches.
        mrc     p15, 0, r2, c1, c0, 0
        bic     r2, r2, #CPU_CONTROL_MMU_ENABLE
        mcr     p15, 0, r2, c1, c0, 0


Of course, if the MMU is off, you don't get caches on < ARMv6 (and I don't know about ARMv6 because I've never done any low-level work on one) because they're all virtually-indexed, etc.

gzboot relocates itself out of flash and into RAM (well, this is configurable in the Makefile/ldscript per board), so you could always add a board-specific setup hook that mapped RAM VA==PA and turned on the MMU, I$, and D$. That would probably provide a ... monumental speed-up.

OF course, before jumping into the kernel, you'd want to flush / disable the caches and MMU in another board-specific hook.

This means that you'd have to add processor-specific routines to evbarm/stand for managing the cache, but that probably wouldn't be that big of a deal.


-- thorpej

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