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| -rw-r--r-- | doc/README.mips | 57 |
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diff --git a/doc/README.mips b/doc/README.mips new file mode 100644 index 0000000..85dea40 --- /dev/null +++ b/doc/README.mips @@ -0,0 +1,57 @@ + +Notes for the MIPS architecture port of U-Boot + +Toolchains +---------- + + http://www.denx.de/wiki/DULG/ELDK + ELDK < DULG < DENX + + http://www.emdebian.org/crosstools.html + Embedded Debian -- Cross-development toolchains + + http://buildroot.uclibc.org/ + Buildroot + +Known Issues +------------ + + * Little endian build problem + + If use non-ELDK toolchains, -EB will be set to CPPFLAGS. Therefore all + objects will be generated in big-endian format. + + * Cache incoherency issue caused by do_bootelf_exec() at cmd_elf.c + + Cache will be disabled before entering the loaded ELF image without + writing back and invalidating cache lines. This leads to cache + incoherency in most cases, unless the code gets loaded after U-Boot + re-initializes the cache. The more common uImage 'bootm' command does + not suffer this problem. + + [workaround] To avoid this cache incoherency, + 1) insert flush_cache(all) before calling dcache_disable(), or + 2) fix dcache_disable() to do both flushing and disabling cache. + + * Note that Linux users need to kill dcache_disable() in do_bootelf_exec() + or override do_bootelf_exec() not to disable I-/D-caches, because most + Linux/MIPS ports don't re-enable caches after entering kernel_entry. + +TODOs +----- + + * Probe CPU types, I-/D-cache and TLB size etc. automatically + + * Secondary cache support missing + + * Centralize the link directive files + + * Initialize TLB entries redardless of their use + + * R2000/R3000 class parts are not supported + + * Limited testing across different MIPS variants + + * Due to cache initialization issues, the DRAM on board must be + initialized in board specific assembler language before the cache init + code is run -- that is, initialize the DRAM in lowlevel_init(). |