Retro Replay

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Retroreplay pp.jpg

Retro Replay was iComp's kickstarter into the retro market: Announced on april 1st, 2001, people were discussing if the announcement would be an april fool. The unit was released in september 2001, and a total of three production runs were made until 2006.

Retro Replay is not manufactured any more, but it continues to live as a construction kit called "Nordic Replay", which has slight modifications in memory mapping in order to allow using the "Nordic Power" ROM images. The following register description still applies to the cartridge.

Contents

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= (Commodore) 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 the Replay Resources. 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.

Technical data in detail:

  • the read $de00 bug has been removed
  • the freeze-logic has been re-developed "from scratch" and it's much more secure than any other freezer before
  • The buttons are of much higher quality than those of the original-AR
  • the Freeze-key is digitally softened (no lockup on freeze)
  • Software-switchable IO-area, so a REU can be used at the same time.
  • FlashROM is programmable from C64 without additional equipment
  • Two different ROMs can be used and selected with a hot-pluggable jumper. (Think of one being PAL and the other one NTSC, or having other different ROM versions on the same cart.)
  • 32K RAM and 128K for ROM allow adding lots of features to the software
  • The new board fits into many existing covers (shipped without cover!)
  • Expansionport on the cartridge allows connecting the RS232-Interface Silversurfer (theoretically up to 460800 Baud, 16 Byte Fifo) or RR-Net
  • Gold plated contacts

Technical Documentation

The instruction sheet that came with the cartridge as available in English only, and has not been changed over the course of three small production runs.

Inside_Replay.txt contains the original technical documentation.

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. 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 have no effect until some IRQ comes along - this includes a BRK. The FreezeDone Flipflop is reset by setting bit 6 of the $de00 register, activating the standard memory map of the cartridge.

Registers

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 Description
7 bank-address bit 15 for ROM banking
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.
5 switches between ROM and RAM: 0=ROM, 1=RAM
4 controls bank-address bit 14 for ROM and RAM banking
3 controls bank-address bit 13 for ROM and RAM banking
2 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.
1 controls the EXROM line: A 0 will assert it, a 1 will deassert it.
0 controls the GAME line: A 1 asserts the line, a 0 will deassert it.

$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 Description
7 bank-address bit 15 for ROM banking (mirror of $de00)
6 REU compatibility bit. 0=standard memory map 1=REU compatible memory map
5 bank-address 16 for ROM (only in flash mode)
4 controls bank-address bit 14 for ROM and RAM banking (mirror of $de00)
3 controls bank-address bit 13 for ROM and RAM banking (mirror of $de00)
2 NoFreeze (1 disables Freeze function)
1 AllowBank (1 allows banking of RAM in $df00/$de02 area)
0 enable accessory connector. See further down.

$de00 read or $de01 read

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

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.

Flash mode

Bits 0 and 1 of $de00 are active _only_ in the $8000-$9fff range, other areas will behave as if no cartridge is connected. Bit 5 can be used to map in the RAM if needed, and bit 2 can be used to disable the cartridge completely.

For compatibility reasons using only regular "ultimax" mode is recommended.

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 danger 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 indicates 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 - it is inherent in the technology. Before programming, a sector should be erased.

chip erase

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 we 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 C64 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). We suggest a timeout of 60 seconds for a 16K sector.

Making flash chip version 29F010B work

Please note that "multiple sector erase" fails on some chip revisions. 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 all else fails, just erase every sector by itself.

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.

The accessory connector is compatible with the Silversurfer, RR-Net and MP3@64. 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!

Further 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 registers. This could be used as an additional key, a hidden-key or whatever you want to use it for.

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