What documentation are you referring to? The docs with the Monitor
cart? or something else?
-Matt Pritchard
Graphics Engine and Optimization Specialist
MS Age of Empires & Age of Empires ][
> -----Original Message-----
> From: Keith Henrickson [SMTP:flipper@xxxxxxxx]
> Sent: Friday, June 05, 1998 12:06 AM
> To: stella@xxxxxxxxxxx
> Subject: [stella] Atari 7800 programmers reference
>
> This is a preliminary programming doc for the atari 7800. It is
> incomplete and probably inaccurate if not just plain wrong. I am well
> aware that the documentation for the system was sold at one point, but
> last I contacted the company that was selling it, they didn't think
> they
> had any left after the backorders were filled. Even if they did, I
> don't
> have the $150 they wanted. Since no one who was lucky enough to get
> one
> of these kits has made a posting of any docs as far as I have seen,
> I've
> started poking through the BIOS ROM to see how it worked. If anyone
> can
> fill in any details, or better yet post the docs that they have, that
> would be great.
>
> Keith Henrickson
> flipper@xxxxxxxx
> 6/1/98
>
> ----------------------------------------------------------------------
> --
>
> Memory map:
>
> $0000-$0FFF - Probably IO devices, some RAM as well.
> $1000-$3FFF - RAM, total of 4K, some kind of mirroring will occur.
> $4000-$FFFF - Available to the cart port, all read/write?
>
> ----------------------------------------------------------------------
> --
>
> Startup of a cart:
>
> There is a vector at $FFF8 that tells the authentication system where
> to
> look for the 'signature block', although I do not currently have the
> format of the block itself. Several checks are performed to determine
> the
> 2600/7800 cart:
>
> 1. If the RESET vector ($FFFC) is $0000 then go 2600.
> 2. If the RESET vector ($FFFC) is $FFFF then go 2600.
> 3. If the low bit of $FFF8 is 0, then go 2600.
> This means the auth table must occupy an odd numbered address.
> 4. If the high nibble of $FFF8 is not $F, then go 2600.
> This means the auth table must occupy the $xxFx block of memory.
> 5. If the low nibble of $FFF9 is not $3 or $B then go 2600.
> This means the auth table must start at $x3xx or $xBxx.
> 6. If $FFF9 is less than $40, then go 2600.
> The auth table MUST sit higher than this, as $4000 is the start of
> ram.
> 7. If $FFF9 - 1 is less than the RESET vector ($FFFC) than go 2600.
> The auth table must sit somewhere between the start of program code
> and the end of ram.
> 8. Finally, if the low nibble of $FFF9 is $B, the title screen is
> skipped.
>
> If all of these requirements are satisfied, then the BIOS will attempt
> to
> authenticate a cart. Unfortulately due to the 760 bit public key
> system
> used for authentication, cracking the key is beyond the capibilities
> we
> have today. If someone has more details (key size less than 760 bits
> or
> better yet, the key itself), then maybe something will open up along
> these
> lines.
>
> ----------------------------------------------------------------------
> -----
>
> The 7800 seems to use a display list, as did the 5200, although it is
> far
> more complicated. The Maria chip is a little-endian processor, versus
> the
> 6502 microprocessor that is big-endian. Be careful when specifying
> memory
> addresses in your display lists.
>
> The high byte of the master display list is stored at $002C, and the
> low
> byte at $0030. The format of the master display list is as follows.
> There are a series of 3 byte entries. I don't know yet how many 3
> byte
> entries there are supposed to be. Each entry takes the following
> format:
>
> +-----------+-----------+-----------+
> | byte 1 | byte 2 | byte 3 |
> +-----------+-----------+-----------+
> | H | L | High byte | Low byte |
> +-----+-----+ of second | of second |
> | C | R | display | display |
> | o | e | list | list |
> | m | p +-----------+-----------+
> | a | e | |
> | n | a | |
> | d | t | |
> +-----+-----+-----------+-----------+
>
> Each entry is used for 'repeat' lines on the screen. The command
> nybble
> is unknown, but so far my guesses are:
>
> 8 - Set bitmapped mode, one color per screen line.
>
> --------------------------------------
>
> The Secondary Display List
>
> This seems to be a very powerful configuration list, but it has a very
> difficult format. However, this is where the actual drawing to the
> screen
> happens. Once you have a secondary display list to draw a certain
> type of
> screen line (blank line, solid line, whatever your heart can come up
> with), you can call it as many places you like in the master display
> list.
>
> Each entry can have a variable number of bytes in it, but all entries
> end
> with two consecutive zeros. Separate sub-functions in one secondary
> display list entry are separated by a single zero byte.
>
> The basic 'mono bitmap' mode entry seems to be six bytes long:
>
> +----------+-----------+-----------+--------+----------+----------+
> | Low-byte | Data size | High-byte | Offset | zerobyte | zerobyte |
> | of graph | | of graph | | | |
> | data | | data | | | |
> +----------+-----------+-----------+--------+----------+----------+
>
> The graphdata pointer simply points to the beginning of the
> variable-length graphics data itself. To set how much graphics data is
> drawn, set the 'data size' byte to $20-(number of bytes of graphdata).
>
> INFO NEEDED: values greater than $20 seem to be valid too. What is
> going
> on?
>
> The offset is the horizontal delay in pixels times 2. This is used to
> align pieces of graphics data of varied size on the screen. For
> instance,
> the atari logo on the boot screen uses the fewest number of bytes
> needed
> to hold the section of the 'arch', increasing as the logo symbol gets
> wider. Then they are centered on the screen by using the 'offset'
> location.
>
> INFO NEEDED: How does one set the colors??
>
> ----------------------------------------------------------------------
> -----
> Chip Registers:
>
> $0028 -- VBLANK status.
>
> +---+---+---+---+---+---+---+---+
> | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
> +---+---+---+---+---+---+---+---+
> | V | --------UNUSED----------- |
> | B | |
> | L | |
> | A | |
> | N | |
> | K | |
> +---+---+---+---+---+---+---+---+
>
> VBLANK - 0 : Not within VBLANK area.
> 1 : Within VBLANK area.
>
> ------------------------------------------
>
> $002C - High byte for master display list
> $0030 - Low byte for master display list
>
> ------------------------------------------
>
>
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