Andre Schwarz wrote: > Jerry Van Baren schrieb: >> Andre Schwarz wrote: >>> In "cpu/mpc83xx/start.S" there is a comment : >>> >>> /* >>> * The Hard Reset Configuration Word (HRCW) table is in the first 64 >>> * (0x40) bytes of flash. It has 8 bytes, but each byte is repeated 8 >>> * times so the processor can fetch it out of flash whether the flash >>> * is 8, 16, 32, or 64 bits wide (hardware trickery). >>> */ >>> >>> This does _not_ hold true for all configurations. Flash is simply one >>> of many options ... >>> Maybe it's true for the Freescale boards. >>> >>> Other sources of the HRCW can be hard-coded strapping pins or an I2C >>> EEPROM. >>> >>> Why is there a need to define the HRCW ? >>> >>> regards, >>> Andre Schwarz >> >> Hi Andre, >> >> The HRCW in flash (could be other memory or a FPGA register) is a >> processor feature which a board may or may not use. I am not familiar >> with the whole 83xx family, but I presume the feature is part of the >> whole family. >> >> As you point out, there are other ways of configuring the processor on >> power up, and it is board-specific which way is used on the particular >> board. >> >> For the boards that support the HRCW, obviously the definition in the >> first 64 bytes of flash is necessary. For other boards, it is >> unnecessary. FWIIW, the Freescale eval boards that I have experience >> with allow the HRCW to come from flash, i2c, or an FPGA (BCSR). >> >> To date, having a potentially unused HRCW definition in memory has not >> been an issue - people either use it or ignore it. If it is an issue, >> you could use conditionals to disable it. I'm sure the 83xx custodian >> (Kim Phillips) would consider patches to do that. ;-) Note that >> there is a possibility that some of the code assumes the presence of a >> HRCW, so you would have to inspect and/or regression test as part of a >> conditionalization patch. >> > ok - so should be no problem to #define the HRCW to "0x0" since it won't > be used at all - just occupies some memory. > I just wanted to be sure that the #defined HRCW is not used as a > reference at all in any code !
Theoretically, there is no problem. I don't know if there are any implicit uses of the HRCW - that would be part of the need to inspect and/or regression test. I suspect that the CPU frequency determination code uses it, since part of the CPU PLL multiplier comes from the HRCW (IIRC - I get confused between the 82xx and 83xx families sometimes). [snip] Best regards, gvb ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ U-Boot-Users mailing list U-Boot-Users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/u-boot-users
