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The Fine Manual
AtoMMC2 provides modern mass storage for the classic British Atom computer. It is a combination hard/software solution designed to fit inside the Atom's case without unusual modifications to the machine. It provides full read and write access to files on a FAT formatted MMC or SD/SDHC card. It will work on any Atom computer as it doesn't require RAM, ROM or hardware expansions.
Read on or jump to:
- Initialisation
- Adding software to the card
- Firmware reference
- The 'user port'
- Upgrading the interface's firmware
- Troubleshooting
The interface attaches to PL8, a 20 pin dual-row header on the Atom's main board. This header may not be fitted if the Atom was built from a kit. It is a very simple job to fit, if required, but take care to locate it pins up on the keyboard side of the main board, where the white outline is present, with soldering on the component side. With the connector on the wrong side the pin ordering will be reversed and damage to Atom and interface will occur. The header and interface are connected by the 20 way wire jumper. The interface connector can only fit one way and it would be awkward to fit the Atom end of the cable incorrectly but just in case please note the small triangle on the cable connector. This indicates pin 1. The location of pin 1 on PL8 is indicated by a small white dot on the Atom PCB.
The interface is usually mounted inside the Atom's case. This may be achieved by any method which will electrically/spatially insulate the interface from the Atom's main board. My recommendation is to put a 90 degree bend in the main cable and situate the interface in the base of the case, looping the cable over the right-hand edge of the PCB, avoiding the mounting hole. Care must be taken that the placement of the interface will not interfere with case fitting. 'Servo tape', carpet tape or self-adhesive Velcro strips are recommended fixatives, though leaving it loose is a valid option. The dongle may be tucked inside the case too if access to the card is not required or desired.
AtomMMC may be shipped with the SD card adapter board/dongle attached to the main interface board. It is quite gratifying to snap off the adapter so I leave this for the pleasure of the new owner :D
There are 2 versions of the Atom ROM. One is configured as a service ROM and occupies the memory map in the utility ROM space of #A000->AFFF. Interrupts are used to initialise the system. The second is recommended for users of memory expansion systems with the ability to put code in the DOS ROM memory region at #E000. This version doesn't need interrupt support but requires two small patches to the Atom kernel ROM and naturally precludes the use of Atom DOS without appropriate ROM switching.
This version resides in a 2532 EPROM and should be fitted in the socket marked IC24. Orientation is indicated by the notch in the chip's casing. It should be placed to match the chips around it. Please ensure that the EPROM's legs are not bent during fitting. If any do suffer an unexpected angular distortion, then straighten the affected pin(s) by placing the chip with its legs flat against a solid, flat surface. Gently press the bent leg back into alignment and try again. No damage should occur if the machine is powered up with a bent pin, but the software will fail.
In order for the code to initialise on reset it is necessary for the Atom to receive interrupts generated by the interface board. This may require the fitting of LK3 - a short wire link located to the right of PL8. Without this connection, or with interrupts disabled via configuration, the firmware will have to be initialised manually by typing the following after each reset:
LINK#AFCC
Users of memory expansion boards should follow the procedure for burning the patched kernel and #E000 images into their system. The patched kernel will initialise the firmware at the right time and so no interrupts are needed. LK3 may be left unmade or interrupts can be disabled in the firmware. See the CFG command.
Once the interface and firmware are fitted the machine can be powered up and you should be greeted with a banner announcing the presence of the interface.
ACORN ATOM + ATOMMC2
Holding various keys when hitting BREAK will have effects:
- CTRL will disable the interface firmware until next reset.
- SHIFT will try to execute a file called MENU
- REPT will show additional information in the banner such as the firmware revision and type of card inserted.
Files are simply added to the card using your choice of operating system. Long filenames are not supported. The DOS 8.3 format should be used at all times.
The 'ATM' format is used to ensure Atom files carry their required metadata. It is a 22 byte header conforming to the following standard:
$00 - $0F : File name - Up-to 12 bytes of name + zero padding $10 - $11 : Load address $12 - $13 : Exec address $14 - $15 : Length
Here's the header from Snapper showing the 22 header bytes and the first 10 characters of the main program:
53 4E 41 50 50 45 52 00 00 00 00 00 00 00 00 00 SNAPPER.........
00 29 86 CE 00 13 0D 00 00 52 45 4D 2F 2F 20 53 .).......REM// S
The 16 bit values are stored in little-endian form.
All numeric parameters are specified in hex. No qualifiers such as # or $ are needed. Filenames being passed as parameters to '*' commands do not need quotes. The patched OS routines LOAD and SAVE require them. Optional parameters are shown in parenthesis.
*CAT [*.] (<directory name>) (@<filter character>)
Show a listing of files.
If a directory name is specified then the files in that directory will be listed, otherwise only the files in the current working directory will be shown. You may specify a wild-card character to filter the output. For example, to show only the files starting with the letter Q use the following command:
*CAT @Q
Both a filter and a path may be specified. Order is unimportant. The following commands are equivalent:
*CAT GAMES @S
*CAT @S GAMES
Relative paths are supported. The directory separator token may be specified as '/' or ''. Used alone this token specifies the root directory. The token ‘.’ Represents the current directory, and ‘..’ represents the parent directory, exactly like MSDOS.
Files with their DOS hidden attribute set are never shown. This is useful for hiding data files. Press SHIFT or REPT to pause a long listing. ESC will abort the listing.
*CWD [*CW.] <filename>
Change the current working directory (CWD).
Once the CWD is changed, all file operations are carried out relative to this path.
*INFO [*I.] <filename>
Show the ATM metadata associated with a file.
The metadata is stored in the first 22 bytes of a file. If none is present then junk will be printed as there is no way to know if data is present or not. You should see something like:
SNAPPER 2900 CE86 1300
This shows the load address to be #2900, its execution address to be #CE86 and the file length to be #1300 bytes.
*FATINFO [*F.] <filename>
Show the raw file system information for a file.
The first value shown is the file length in hex. Next is the start sector for the file. A reserved value of zero follows, then the DOS attribute byte.
LOAD <filename>
Load a program into the currently selected text page.
The file's metadata is printed unless suppressed with the command *NOMON.
*LOAD [*L.] <filename> (<load address>)
Load a file exerting control over its placement in memory.
Omitting the load address will load the file into the location specified in its metadata, otherwise data will be placed in memory starting at the specified address. The file's metadata is printed unless suppressed with the command *NOMON.
*RLOAD [*RL.] <filename> <address>
Load a file exerting control over its placement in memory.
This command uses the raw length of the file as reported by the file system rather than that stored in metadata, which may not be present.
The file's metadata is printed unless suppressed with the command *NOMON.
*RUN [*<filename>] <filename> (<parameter>...<parameter>)
Load and attempt to execute a program.
The firmware attempts to run all programs even if they were not intended to be auto-running. In some cases this will produce an error in which case the normal load & run sequence should be used. Any parameters following the filename will be relocated to the input buffer at #100. If no parameters are given #100 will contain return (#0D).
*EXEC [*E.] <filename>
Present the specified file's content to the Atom as if it had been typed.
Files read in this way should be ANSI text files. This is a useful way of entering programs which only exist as listings.
SAVE <filename>
Save the current program.
Memory from the start of the current text page to the value of TOP is written to the specified file. If a file with the same name already exists you will be prompted to overwrite it.
*SAVE [*S.] <filename> <start> <end> (<exec>)
Save a block of memory.
The end address is exclusive - in other words it is the address of the byte after the last byte to be written. The execution address will be set to the start address if not specified.
*DELETE [*D.] <filename>
Delete the specified file from the card.
*HELP [*H.]
Show some useful information.
The remaining commands are related to the operation of the interface.
*CFG [*CF.] (<value>)
Set/get interface configuration bits.
Specifying a value will set the configuration bit values, omitting it will cause the current configuration value to be displayed. All values are specified and shown in hex. The default value is FF. The following bits have an effect:
- 5 (20) - Enable Interrupts
- 6 (40) - Shift-Break Action
- 7 (80) - Enable Boot loader
In order to disable interrupt generation the following command could be issued:
*CFG C0
Warning: Extreme care should be taken when changing the configuration bits. Certain combinations may have undesirable effects on the operation of the hardware. The most dangerous combination is disabling the boot loader when no firmware is flashed. This will result in an endless loop which cannot be aborted. The only way to reverse this action is to remove the PIC and use a dedicated PIC programmer to change the configuration byte in EEPROM.
Holding shift at boot-time will insert the string *MENU into the keyboard buffer and thus try to execute a program with that name. It may be desirable to have this done on every reset, and so you can invert the shift-key detection sense with bit 6. This way the menu is executed unless the shift key is held.
The interface features an 8-bit bidirectional user port – known affectionately as PORTB. The data direction for each pin on the port is independent and user selectable. The directions and values are stored in EEPROM and will be restored on power-up.
*PBD (<value>)
Set/get the PORTB direction configuration.
1 is 1nput, 0 is 0utput. FF will set all pins to input. 0 will set all to output.
*PBV (<value>)
Set/get the state of the PORTB pins.
Setting the state of a pin which is configured as an input will latch the specified value but otherwise have no effect. Reading the state of a pin set as an output will show the value last latched to that pin. The port will sink way more current than it can source, so it is recommended to use the port in ‘open collector’ mode:- make the pin an input and tie the driven line high using a resistor. Change the port to output and drive it low in order to present a logic low level. Here is a diagram showing the pin ordering on the board. The view is of the main interface PCB, top-left component side.
Pin 7 Pin 0
V V
+---||||||||-------…
| ++++++++
The interface firmware may be upgraded using the built-in boot loader. The procedure is as follows:
- Ensure the version of the firmware being flashed is compatible with the available Atom firmware.
- Ensure the boot loader is enabled.
- Obtain the latest PIC firmware files.
- Format a card and copy the firmware file to it.
- Insert the card and reset/power cycle the Atom.
- The interface will light both LEDs and flash the green whilst the firmware is flashed.
- The LEDs will extinguish. Remove the card and reset the Atom.
The boot loader is robust but there may be combinations of firmware updates which require further steps. Call your support representative for further assistance.
- If no banner is shown at reset:
- A000 version: Check that interrupts are enabled
- E000 version: Ensure ROM is correctly loaded and that the kernel ROM is patched.
- Solid green light on reset:
- Re-flash firmware.
- CARD? is shown when accessing the card:
- Try a different brand of MMC/SD/SDHC card.
- No response from interface / card accesses hang:
- Ensure dongle connections are correct, ensure PL8 connection is correct.
- Flames come from Atom case:
- This is pretty normal. Remove/bypass regulators and supply a healthy 5V.
Revised 20/05/2011
The Atom Technical Manual at Chris's Acorns