Some problem about code reading

[enorm]

Hi,
  I met some problems when reading sourcecode of u-boot 1.1.4 (for mpc85xx)

file /cpu/mpc85xx/start.s line 276


276.    #if (CFG_CCSRBAR_DEFAULT != CFG_CCSRBAR)
277.    /* Special sequence needed to update CCSRBAR itself */
278.    lis r4, CFG_CCSRBAR_DEFAULT at h
279.    ori r4, r4, CFG_CCSRBAR_DEFAULT at l
280.
281.    lis r5, CFG_CCSRBAR at h
282.    ori r5, r5, CFG_CCSRBAR at l
283.    srwi r6,r5,12
284.    stw r6, 0(r4)
285.    isync
286.
287.     lis r5, 0xffff
288.     ori r5,r5,0xf000
289.     lwz r5, 0(r5)
290.     isync
291.
292.    lis r3, CFG_CCSRBAR at h
293.    lwz r5, CFG_CCSRBAR at l(r3)
294.     isync
295.    #endif


I think it means if we don't use default CCSRBAR, we put the CCSRBAR addr actually used to the proper place in default CCSRBAR, so that it can jump to the addr we want to automatically.(line 276-286).

But, I don't know what line 287-294 does. Can some one tell me pls? 
Thanks for your help. 
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