| |
Documentation for the Retro Replay freezer cartridge for the C-64
This document is freely distributable as long as it is not changed, and one
of the sources www.jschoenfeld.com, www.jschoenfeld.de, www.siliconsonic.com
is mentioned.
last update: September 28th, 2001
--
September 28th:
Last-minute change: The Freeze button of my pre-series prototype failed
today! This brought me to the decision to send the MT250 type buttons back
and use Monacor MT412 buttons instead. They are much more expensive (more
than twice as much!), but they make a much better impression. I know my MT250
button on the pre-series board had to take a lot since june this year, but I
don't want to risk returns from all over the world because of bad buttons.
SMD and conventional production is finished, quality control will follow this
weekend, first shipments on monday, october 1st!
(fortunately, the buttons are mounted after QC, so this does not cause
additional work :-)).
Corrected the "accessory connector" chapter of this document.
Corrected the "hints" chapter of this document.
--
September 26th, 11:30am:
Decided to leave bit 0 of $de01 register "write-always", so the UART can be
switched on and off during operation. This ensures higher compatibility with
other hardware. Last chance to change something in the behavior of the Retro
Replay is over now, programming the MACHs will begin in a few minutes!
--
September 26th, 2:00am:
Accessory connector was only available in REU compatible mode. Nonsens! Don't
ask me why I did this, now the accessory connector can be switched on
regardless of the REU compatibility bit.
Decision pending: set/reset accessory enable bit regardless of first write
to $de01? Right now it's "write once and suffer from your decision". Could be
changed for the final version, we have about 12 hours left for the decision!
--
September 19th:
Removed another glitch in the logic that kept the Flash from accepting the
"magic" sequences such as "Autoselect" and "Read/Reset". The problem was an
interruption of the write cycle of about 5 nanoseconds after about 250ns. This
caused the 29F010 Flashrom to recognize two write cycles instead of one, so
an error in the sequence was detected, and the device stayed in read mode
forever.
Problem solved by generating the signal with a T-Flipflop instead of a
combinatoric equation. Thanks to my Agilent 54622D mixed-signal scope for
being such a precise device. Now I know why I decided for the 100Mhz version
instead of the cheaper 60Mhz version, but I did not expect it to be useful on
the slowest computer that I ever developed for.
All other combinatoric equations of the design do not cause glitches like this
(either uncritical, or they form RS-flipflops that are stable by default). No
further problems expected from this cause.
Further, the memory map changes possible with the lower two bits of the $de00
register have been cut to a minimum. You can only alter the $8000-$9fff area
with the GAME and EXROM lines if the Flashmode jumer is set. This ensures
IRQs and NMIs to be served correctly, even if the GAME line is asserted,
which usually also disables the kernal rom in the $e000-$ffff area. With this
improvement, you can write basic programs with small assembler-subroutines
for the magic sequences. Don't try POKE-ing the magic sequences, as the POKE
command also reads from the location you want to write, so you'll never
produce a proper magic sequence.
Updating will not have to be done, the September 18th version never left this
house!
Software compatibility is not affected by these changes.
--
September 18th:
In preparation for mass production, some changes in RAM and FLASH timing
have been done. Certain combinations of MACH and RAM had problems with data
loss in the memory. This is also the cause for the failure of earlier Flash
programs. Sorry Count0!
Write cycles have now an earlier end, this ensures data hold times for both,
Ram and Flash chips. This improvement also applies to the accessory connector.
A write cycle is now exactly three dot-clock cycles long, which is about 380
nanoseconds on PAL machines. Both edges of the signal occur during the
data-valid window of the CPU write cycle, so a secure takeover of data into
the receiving chip is ensured for all vendors of memory chips and
Amiga-clockport expansions.
This change cannot be implemented on the beta board (green board) due to
routing limitations in the MACH chip. Pins had to be swapped and glue logic
had to be added to the final board in order to make the design fit. If you
have one of the four beta boards, keep it as a collector's item. Two of them
are back at individual Computers, maybe we will auction them on eBay (anybody
interested?).
Software compatibility is not affected by these changes.
--
May 17th:
Changed interrupt level of 22-pin port to NMI. Thanks to Ninja for the
suggestion, this will ensure safe serial data transfer also at high
baudrates.
22-pin port will now be equipped on all boards. Found a good supplier
of raster-2 pin headers, so now this can be financially justified.
Still looking for case supplier. We want black or transparent cases!
Printed circuit board (PCB) finalized. The board will have black solderstop
and golden connectors. We want it to be durable!
--
April 21st:
Added passage to "Flashing Rom" section, added hardware options of
final board.
--
April 19th:
Updated after the Ma Baker conference at McDonalds Fallingbostel on
April 15th, 2001. Thanks to these scene members: Danzig, Deekay, Doc Bacardi,
Ninja, Checky and Count0 (no special order!). Each of them has done his part
in improving the cartridge with suggestions.
Implemented suggestions:
- REU comp bit moved to bit 6 in $de00/01 read register
- AllowBank bit introduced ($de01 write, bit 1, only affects RAM)
- NoFreeze bit introduced
- accessory connector added
suggestions not implemented:
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. This would have caused too many changes that would make other
A1200 hardware incompatible on this port. Sure, this port will be used for
a Silversurfer serial port by most users, but you could also think of any
other piece of hardware that uses the Amiga 1200 clockport. This would not
be possible with that change.
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 somputer, 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.
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 apped 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 exampe (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.
512K Flash option
------------------
The final board has the option to install a 29F040 Flash rom (also AMD). I am
not sure whether this will ever be done, because these parts are really
expensive (about 40,- DM each, information from April 2001). However, with a
special MACH version that is still to be made, a 512K Flash can be installed,
at the cost of having no accessory connector. The two pins necessary will be
used for further banking bits, so the accessory connector MUST stay free!
If you have any questions, feel free to ask me via e-mail:
jens@jschoenfeld.de
--EOF
|
| |