3 ms·

Ha, I remember the Atari ST palette at $ff8240. Good memories, very similar to mine. I miss my Atari and Amiga.

Annatar 9y ago
What Atari ST palette at $ff8240? That address seems to be in the A500 KickStart 1.2 or 1.3 address space... My interest is piqued.
- jacobush 9y ago
  Atari is another computer altogether.
  - Annatar 9y ago
    An excerpt from the original post I replied to: “Ha, I remember the Atari ST palette at $ff8240.” To which you replied: “Atari is another computer altogether.” I know, I own an ATARI Falcon 030 in addition to two Amigas! A HackerNews in 2018 is explaining to me that an ATARI ST is a different computer... only on “Hacker News”! I was there and then, I worked on both an Amiga and an ATARI ST!
    - jacobush 9y ago
      Sorry. I thought you didn't know about Ataris. $ff8240 seems to actually be an Atari address: http://atari-forum.com/viewtopic.php?t=8327 http://atari-forum.com/viewtopic.php?t=8327 not an Amiga address.
- vardump 9y ago
  68000 reset vector is at address 0x4. In case you were thinking reset vector is somewhere at end of addressable memory. Location of the reset vector is pretty weird, since at least Amiga got chip RAM over that region. I guess there must be some special hardware that makes 68k read a different value from address 0x4 only momentarily after the system has been powered on.
  - Annatar 9y ago
    $4 is the address of the exec.library, the entry point into the kernel (“exec” in Amiga terms), not the reset vector.
    - vardump 9y ago
      No, it really is the reset vector for 68000 chip itself. In addition to being exec library vector after being powered up! Quick googling found this for example: https://retrocomputing.stackexchange.com/questions/1158/why-is-the-amiga-rom-at-a-high-memory-location-and-ram-in-low-memory/1176 https://retrocomputing.stackexchange.com/questions/1158/why-... "When a 68000 CPU powers up, it reads a few words at memory location zero to get the initial stack pointer and program counter. That suggests to me that a computer system designer would put the system ROM at memory location zero, where the 68000 would read the initial SP and PC when coming out of reset. However the Amiga puts RAM at location zero, and the ROM at the very far end of the address space. It has a hardware switch which causes the system address decoding to place a second copy of the ROM at location zero, hiding the RAM. At reset, this hardware switch is "on", so the 68000 reads the initial SP and PC from this mirrored copy of the ROM and starts executing. Then the ROM firmware switches the hardware switch "off" to remove the mirrored ROM and reveal the RAM again."

What Atari ST palette at $ff8240? That address seems to be in the A500 KickStart 1.2 or 1.3 address space... My interest is piqued.

jacobush 9y ago
Atari is another computer altogether.
- Annatar 9y ago
  An excerpt from the original post I replied to: “Ha, I remember the Atari ST palette at $ff8240.” To which you replied: “Atari is another computer altogether.” I know, I own an ATARI Falcon 030 in addition to two Amigas! A HackerNews in 2018 is explaining to me that an ATARI ST is a different computer... only on “Hacker News”! I was there and then, I worked on both an Amiga and an ATARI ST!
  - jacobush 9y ago
    Sorry. I thought you didn't know about Ataris. $ff8240 seems to actually be an Atari address: http://atari-forum.com/viewtopic.php?t=8327 http://atari-forum.com/viewtopic.php?t=8327 not an Amiga address.
vardump 9y ago
68000 reset vector is at address 0x4. In case you were thinking reset vector is somewhere at end of addressable memory. Location of the reset vector is pretty weird, since at least Amiga got chip RAM over that region. I guess there must be some special hardware that makes 68k read a different value from address 0x4 only momentarily after the system has been powered on.
- Annatar 9y ago
  $4 is the address of the exec.library, the entry point into the kernel (“exec” in Amiga terms), not the reset vector.
  - vardump 9y ago
    No, it really is the reset vector for 68000 chip itself. In addition to being exec library vector after being powered up! Quick googling found this for example: https://retrocomputing.stackexchange.com/questions/1158/why-is-the-amiga-rom-at-a-high-memory-location-and-ram-in-low-memory/1176 https://retrocomputing.stackexchange.com/questions/1158/why-... "When a 68000 CPU powers up, it reads a few words at memory location zero to get the initial stack pointer and program counter. That suggests to me that a computer system designer would put the system ROM at memory location zero, where the 68000 would read the initial SP and PC when coming out of reset. However the Amiga puts RAM at location zero, and the ROM at the very far end of the address space. It has a hardware switch which causes the system address decoding to place a second copy of the ROM at location zero, hiding the RAM. At reset, this hardware switch is "on", so the 68000 reads the initial SP and PC from this mirrored copy of the ROM and starts executing. Then the ROM firmware switches the hardware switch "off" to remove the mirrored ROM and reveal the RAM again."