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Modify NeXT ROM Mac address on OS X

 
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barcher174



Joined: 07 Dec 2012
Posts: 560

PostPosted: Mon Nov 21, 2016 11:42 pm    Post subject: Modify NeXT ROM Mac address on OS X Reply with quote

All,

I wrote a short guide on modifying the MAC address in a next ROM using OS X here:

http://www.asterontech.com/Asterontech/NEXTCube_ROM_MAC_Address.html

The MAC address for NeXT networking is contained in the ROM file. The available ROM revisions for download will not contain a unique MAC address. If you only have a single NeXT this shouldn't be a problem. If you want to network multiple Nexts you need to be sure they have unique addresses. Further, some software is locked to the MAC address. In this case it is important to have the proper MAC address to validate the software.

Step 1) Download the proper ROM for your machine
http://www.nextcomputers.org/NeXTfiles/Software/ROM_Files/

Step 2) Download a HEX editor
http://ridiculousfish.com/hexfiend/

Step 3) Open the ROM in a HEX editor. Pictured below the MAC address (Red box) is matched between the ROM monitor and the hex editor. Use the Find and Replace fields to change the address to the desired value. Note the syntax, where a single value in the MAC address is always preceded by a '0'. We are not quite done. You will need to calculate the CRC32 value for this part of the ROM. The CRC value is calculated using the HEX string starting with byte 0 and ending right before the start of the CRC value.

Step 4) Launch a TCL shell. You will need to load the CRC32 package. Then we will define the HEX string as binary (the default is ASCII which will not work). Finally we calculate the CRC32 value and output as HEX.

Step 5) Search and replace the old with the new CRC value. You can verify the ROM for completeness using the previous emulator. After you have confirmed it will boot, it is now safe to program the real ROM chip.
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t-rexky



Joined: 09 Jan 2011
Posts: 273
Location: Snowy Canada

PostPosted: Tue Nov 22, 2016 3:44 am    Post subject: Reply with quote

Very concise information, thank you or putting it together! It took me a while to dig up the required information when I did mine a few years back. I recall that I used a HEX editor on OS X that allowed me to calculate the checksum straight in the editor, based on selected content of the file.

I would also highly recommend the services of Steph at http://www.eprompro.com for those who do not have their own burners.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Thu Nov 24, 2016 10:33 am    Post subject: Reply with quote

Path Finder has an integrated HEX editor. And you can also use online services like http://www.sunshine2k.de/coding/javascript/crc/crc_js.html to calculate CRC checksums.
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