Inside Replay Essentials.txt

Inside_Replay_Essentials.txt is a rewritten version of the original documentation and is used during development of the user ROM only. The FlashMode e.g. is not described at all.

Someone (not at the Ma Baker conference) suggested that the freeze button
can be pressed through a serial port that is connected to the accessory
connector. 
Hardware-turn-off switch/jumper: This is absolutely unnecessary. After
setting bit 2 in $de00, the cartridge is completely switched off, and it is
impossible to tell by software if there is a Retro Replay installed or not
(and I mean "impossible", because the hardware is completely tri-stated!).

Compatibility to the IDE64 controller: This is not necessary. That thing is
overpriced and crappy. Nobody can really use it. Demos and games have their
own loaders that do not work with a harddrive, and there are simply not
enough customers with such a harddrive to justify such a major change in
hard- and software. Period.
--
** No further changes to the hardware will be made. This is nealry a
** non-profit project, I will not spend more time with it.
(unless you have a really good suggestion that increases the value by far!)


General
-------
Retro Replay is a cartridge that is plugged to the 44-pin expansion slot of
all known C-64 versions. Opening the computer is not necessary. It has been
successfully tested on C-64 models from 1983, 1984, the cost-reduced C-64
with the highly integrated PLA, the C-64 game system, and the SX-64. The
machines tested were all PAL machines. NTSC machines were tested by Jeri
Ellsworth. If used on a C128, the module will not force the computer to start
in C64 mode. It will only start if you enter "go64", or if you hold down the
C= key during startup, so you don't have to remove the cartridge for the C128
mode.
Essentially, Retro Replay is a revised Action Replay clone. There are a
number of advantages over the real Datel Action Replay, like a more secure
freeze-logic, added amount of ROM and RAM, compatibility to Commodore 1764
REU, and user-flashable ROM without need for additional equipment like Eprom-
programmers or erasers. Reading $de00 with the cartridge activated will not
crash the computer, as it does with the original Action Replay.
Retro Replay is software compatible with Action Replay, so you can use the
ROM image of your old cartridge on this new product. If you want to do this
legally, you have to be the owner of a real Action Replay. There is no
license aggreement with Datel, because talking to them seems like an
impossible mission. They simply ignored our efforts to contact them.
However, there are free images on the internet that are placed in the public
domain, so nobody really depends on Datel. Check www.ar.c64.org.
The board has the same shape as the original Action Cartridge, so you can put
it in the same case, or leave it without a case at all.


Theory of operation
-------------------
After switching on, the cartridge is a simple ROM module. The $de00 and $de01
registers are active, and the memory map of the cartridge is standard, not
freeze (see further down).
The Freezer is essentially made up of two RS-Flipflops, as with all freezer-
cartridges. However, the Retro Replay has much more sophisticated conditions
for setting and resetting them. Let's call the two Flipflops "Freeze Pending"
and "Freeze done". Both are reset on a hardware reset. Holding the Freeze
button down for more than two microseconds and then releasing it will set the
"Freeze Pending" Flipflop. At the same time, the IRQ and NMI lines are
asserted, and the CPU supervision logic is started: This logic waits for the
CPU to do the necessary write-accesses to stack: Before the 6510 serves an
IRQ or an NMI, the program pointer and the processor status are saved on the
stack ($0100 to $01ff). These three consecutive write cycles give a clear
indication that the CPU will fetch the IRQ/NMI vector in the next cycle, so
this is the set-condition for the "Freeze Done" Flipflop. Setting FreezeDone
resets FreezePending, and disables the Freeze button. Further, the "Freeze"
memory map is set, replacing the original C-64 Kernal IRQ/NMI with the
vectors of the Retro Replay cartridge.
The only way to beat this freezer is to disable IRQs with the SEI command,
and to assert the NMI line with the CIA chip, not telling it to release the
NMI line (NMI is edge-triggered, not level-triggered!). Since nearly no
program runs totally without IRQs, the Retro Replay can be considered as the
"unbeatable freezer" that has been described in one of the "C=Hacking" mags
(although the hardware-description in that article is totally bullshit, no
serious Freezer module has ever used the UltiMax mode of the 64). Even if the
IRQ is served "late" - the CPU supervision circuit is patient. It can wait
forever, and let the computer run without affecting the memory map. If the
program you are trying to freeze has disabled all IRQs and NMIs, the Freeze
button will simply have no effect.
The FreezeDone Flipflop is reset by setting bit 6 of the $de00 register,
activating the standard memory map of the cartridge.


Registers
---------   
The Retro Replay has three registers: Two write-only and one read-only
register:
$de00 write: This register is reset to $00 on a hard reset if not in flash
             mode. If in flash mode, it is set to $02 in order to prevent the
             computer from starting the normal cartridge. Flash mode is
             selected with a jumper.
             Bit 0 controls the GAME line: A 1 asserts the line, a 0 will
             deassert it.
             Bit 1 controls the EXROM line: A 0 will assert it, a 1 will
             deassert it.
             Writing a 1 to bit 2 will disable further write accesses to all
             registers of Retro Replay, and set the memory map of the C-64
             to standard, as if there is no cartridge installed at all.
             Bit 3 controls bank-address 13 for ROM and RAM banking
             Bit 4 controls bank-address 14 for ROM and RAM banking
             Bit 5 switches between ROM and RAM: 0=ROM, 1=RAM
             Bit 6 must be written once to "1" after a successful freeze in
                   order to set the correct memory map and enable Bits 0 and 1
                   of this register. Otherwise no effect.
             Bit 7 controls bank-address 15 for ROM banking

$de01 write: Extended control register. If not in Flash mode, bits 1, 2 and 6
             can only be written once. If in Flash mode, the REUcomp bit
             cannot be set, but the register will not be disabled by the
             first write. Bit 5 is always set to 0 if not in flash mode.
             Bit 0: enable accessory connector. See further down.
             Bit 1: AllowBank  (1 allows banking of RAM in $df00/$de02 area)
             Bit 2: NoFreeze   (1 disables Freeze function)
             Bit 3: bank-address 13 for RAM and ROM (mirror of $de00)
             Bit 4: bank-address 14 for RAM and ROM (mirror of $de00)
             Bit 5: bank-address 16 for ROM (only in flash mode)
             Bit 6: REU compatibility bit. 0=standard memory map
                                           1=REU compatible memory map
             Bit 7: bank-address 15 for ROM (mirror of $de00)

$de00 read or $de01 read:
             Bit 0: 1=Flashmode active (jumper set)
             Bit 1: feedback of AllowBank bit 
             Bit 2: 1=Freeze button pressed
             Bit 3: feedback of banking bit 13
             Bit 4: feedback of banking bit 14
             Bit 5: feedback of banking bit 16
             Bit 6: 1=REU compatible memory map active
             Bit 7: feedback of banking bit 15

Memory maps
-----------

standard:
$de00 and $de01 registers are active, $df00-$dfff contain the last page of
the selected 8K-bank of either ROM or RAM, whatever is selected. RAM can only
be accessed in $8000-$9fff. ROM can be mapped to $8000, $a000 or $e000 with
the corresponding status on GAME and EXROM.
Note: If the AllowBank bit is not set, the $df00-$dfff area will always
access bank 0 of the RAM, so the older cartridge images will work. The
AllowBank bit does not have any effect on the ROM mirror in that area.

Freeze:
ROM is mapped to $e000-$ffff, bank 0 is active directly after Freeze. Writing
to bits 0 and 1 of the $de00 register will have no effect on GAME and EXROM.
RAM can be selected and used in $df00 or $de02, respectively, but not in
$8000. Banking bits work, so you have full read access to the ROM, and access
to up to four RAM pages with the AllowBank bit set (minus 2 bytes if REU
compatible bit is set). You should leave this memory map ASAP by setting bit
6 of $de00, because C-64 RAM in the $e000 area is not available, and you
don't have control of the GAME and EXROM lines.

REU compatible:
$de00 and $de01 registers are active, $de02-$deff contain a mirror of $9e02-
$9eff of the selected 8K-bank of either ROM or RAM, whatever is selected.
RAM can only be accessed in $8000-$9fff. ROM can be mapped to $8000, $a000
or $e000 with the corresponding status on GAME and EXROM. The $df00 stays
free for use with the 1764 Ram Expansion Unit (REU).
Note: If the AllowBank bit is not set, the $de02-$deff area will always
access bank 0 of the RAM, so the older cartridge images will work. The
AllowBank bit does not have any effect on the ROM mirror in that area.


Flashing the ROM
----------------

Retro Replay uses an AMD 29F010 1MBit Flash rom, organized as 128Kx8. If the
Flashmode jumper is not set, writing to the chip is disabled by hardware.
There is no possibility, no undocumented trick or anything else that lets
you write to the Flash. For Flashing, both jumpers must be set. If the
bank-select jumper is not set, you only have access to the upper 64K of the
Flash, which inhibits certain actions described below. It is recommended to
explain this on-screen before trying erase, sector-erase or write operations.
Further, you can try to use banking bit 16 and compare the contents of the
banks you are trying to select. You can display a warning if the contents are
identical, but this is not a proof for an unset jumper, so the user should be
able to override the warning.
All the information below can also be verified from the 29F010 final
datasheet, available on the AMD homepage (160K PDF document). 

Note: For security reasons, the Freeze button is disabled when the Flashmode
jumper is set. Accidential freezing during a flash operation could destroy
data in banks you may not want to alter. The same applies to the Reset-button,
but that cannot be disabled.

Before runnig the following code segments, set bits 0 and 1 of the $de00
register. This will assert GAME and deassert EXROM, bringing the 8K-bank
of the Flash to $8000-$9fff for read and write accesses. This is necessary,
because the cartridge sets $de00 to $02 with the Flashmode jumper set. This
results in a "38911 basic bytes free" message, which may be confusing,
because it shows that no cartridge is installed. Don't be afraid! The
$de00/01 registers are active, and this is only done in order to prevent the
computer to start a possibly garbled ROM. Ideal for development :-)

Read/Reset command:

LDA #$10
STA $de01  ;set bank
LDA #$aa
STA $9555  ;this is a write to $5555 of the chip
LDA #$08
STA $de01  ;set bank
LDA #$55
STA $8aaa  ;this is a write to $2aaa of the chip
LDA #$10
STA $de01  ;set bank
LDA #$f0
STA $9555  ;write $F0 to $5555
LDA #$xx
STA $de01  ;set bank you desire
LDA $xxxx  ;read address you desire

Autoselect command:
LDA #$10
STA $de01  ;set bank
LDA #$aa
STA $9555  ;this is a write to $5555 of the chip
LDA #$08
STA $de01  ;set bank
LDA #$55
STA $8aaa  ;this is a write to $2aaa of the chip
LDA #$10
STA $de01  ;set bank
LDA #$90
STA $9555  ;write $90 to $5555
LDA #$xx
STA $de01  ;set bank you wish to read status from (one of eigt)
LDA $8000  ;read manufacturer code ($01 for AMD)
;do something with the value just read
LDA $8001  ;read device code ($20 for 29F010)
;do something with the value just read
LDA $8002  ;read sector protect information in bit 0. 1=sector protected
;do something with the value just read

Note: Once in Autoselect mode, you can do as many reads from the sectors as
you want. Leaving this mode is only possible with the read/reset command, or
with power-down. Bringing the device into Autoselect mode and then resetting
the machine will let your Retro Replay appear as an empty cartridge. Nothing
to worry about, just power-cycle the computer, and you're back to normal.

Byte program:
LDA #$10
STA $de01  ;set bank
LDA #$aa
STA $9555  ;this is a write to $5555 of the chip
LDA #$08
STA $de01  ;set bank
LDA #$55
STA $8aaa  ;this is a write to $2aaa of the chip
LDA #$10
STA $de01  ;set bank
LDA #$a0
STA $9555  ;write $a0 to $5555
LDA #$xx
STA $de01  ;set bank you desire
LDA #$xx   ;content you wish to write
STA $xxxx  ;write to address you wish to write

Note: Programming means resetting bits from 1 to 0. Programming a 1 into a
bit that already contains a 0 is not possible. The 29F010 chip will give an
error condition in this case, which is not a chip failure - the user has made
the mistake! Consult the AMD document for this case.

The Chip Erase command should not be used, and is therefore not translated
to C-64 assembler in this document. You _can_ use it, but I don't recommend
it. Progam/erase cycles of the Flash memory are limited, and you usually only
alter one of the two 64K banks. The limits are pretty far: Given the 100.000
guaranteed program/erase cycles and an update frequency of "twice a day
including weekends, christmas and easter", we have a product life time of
more than 136 years. Pretty much for a computer product :-).

Sector erase:
LDA #$10
STA $de01  ;set bank
LDA #$aa
STA $9555  ;this is a write to $5555 of the chip
LDA #$08
STA $de01  ;set bank
LDA #$55
STA $8aaa  ;this is a write to $2aaa of the chip
LDA #$10
STA $de01  ;set bank
LDA #$80
STA $9555  ;write $80 to $5555
LDA #$10
STA $de01  ;set bank
LDA #$aa
STA $9555  ;this is a write to $5555 of the chip
LDA #$08
STA $de01  ;set bank
LDA #$55
STA $8aaa  ;this is a write to $2aaa of the chip
LDA #$xx
STA $de01  ;set sector you wish to erase
LDA #$30
STA $8000  ;erase the sector
;the following sequence is optional, called "multiple sector erase".
LDA #$xx
STA $de01  ;set another sector you wish to erase at the same time
LDA #$30
STA $8000  ;erase the sector

then timeout 80 microseconds, and do not access the chip during this period
(your code must be in the 64 memory for this). Then the sector erase
operation will start inside the chip.
After the 80 microsecond pause, start polling $8000 for the results of the
erase operation. For closer information on this, consult the 29F010
datasheet, the /DATA poll section, page 15. A sector erase may take up to 30
seconds, sometimes even longer, because the sector is programmed to $00 prior
to erase (an empty byte contains $ff). I'd suggest a timeout of 60 seconds
for a 16K sector.

Making flash memory version 29F010B work
----------------------------------------
The 29F010B is a drop-in replacement for the 29F010. However, the flash
utility V0.01 and V0.02 can only program the chips, but not erase them.
Due to internal AMD documents, the 29F010 tolerates some violations of the
command sequences, such as not terminating the autoselect command, and
sending another unlock sequence for multiple sector erase. The basic rule is:

Follow the AMD documentation word-by-word, terminate each and every command
with the read/reset command after successful execution, and use the status
given by the chip instead of static timeouts for program or erase operations.

If you need a copy of the changes document, send an eMail. It does not
contain any "confidential" information, and I did not have to sign NDA to
obtain the file, neither will you have to. It's just something that AMD does
not provide on their website publicly.

accessory connector
-------------------
The Retro Replay has an accessory connector that can carry Amiga 1200
hardware. The connector uses the spare_CS signal, not the RTC_CS signal.
This lets you use add-ons like the Silversurfer to add a serial port to the
C-64. The 16 registers of the clock-port are mapped to $de02-$de0f (lower two
registers not available!). The IRQ of that port is connected to the NMI line
of the 6510 processor.

The two missing bytes of the Spare_CS space in non-REU compatible mode will
be no problem, because the Silversurfer is mirrored over that area twice.
Just use $de08-$de0f for the eight registers of the 16c550 UART. I tend to
call this connector the "Silversurfer port", as it will not be able to carry
bigger expansions of the 1200.

Don't just "try" to connect other hardware, as most of the expansions will
not fit mechanically correct. Hypercom 3 for example (old model with direct
connection) would only fit the wrong way round, and this causes a short that
kills both, Hypercom and Retro Replay. Of course, there is no warranty for
this case!

Hints
-----
All jumpers of the Retro Replay are hot-pluggable. Hot-plugging means you
don't have to switch the computer off to change the jumper setting. There is
one thing that you may need this for: After writing to $de01 once, bits 1,2
and 6 are blocked for further writes. If you set and reset the Flashmode
jumper during a session, one more write to the $de01 register including
bits 1,2 and 6 is allowed without having to reset the whole computer. It
will not really make sense for the user, but it may be interesting for
developers.

With Bit 2 in $de01 set, the freeze function is disabled. However, the state
of the freeze button can still be read in bit 2 of the $de00 or $de01 read
register. This could be used as an additional key, a hidden-key or whatever
you want to use it for.