Flash Utility
By Brendan Alford (brendanalford@eircom.net)
Original version by Dylan Smith.
The Diagnostic Board, as it uses Flash memory, is capable of being programmed in-circuit by the Spectrum it is connected to. The Flash utility is provided to aid users in managing ROM images written to the flash memory.
The utility is structured such that it can be built using the sjasmplus assembler. Assuming sjasmplus is on your path, all that needs to be done is to run the build.bat batch file which will build the flash utility, which will be named 'flashutil.bin', and a version designed to live in the flash memory itself, named 'flashutilrom.bin'.
Alternatively, binaries and Spectrum .TAP files containing these binaries are available as part of the release package here, in the FlashUtils folder.
You'll need either a tape containing an audio version of flashutil.tap, flashutilrom.tap and testrom.tap (both from the release package above), or you'll need to hook up a PC to your Spectrum with a set of audio leads, and use PlayTZX to send those three files to the Spectrum.
Before you plug the board into the Spectrum you want to use to program, set the Spectrum/Flash jumper to SPECTRUM (pins 2 to 3). This means the Spectrum will start with its own ROM. Plug the board into the machine, and power it up. You should see the familiar (c) message (or menu on 128K machines).
If instead you see vertical stripes up the screen - the jumper is on the wrong pins. Power the machine down and move the jumper. (The vertical lines are caused by the Spectrum executing RST #38 instructions - 0xFF - in an infinte loop, and the stack overwriting screen memory. Unused or freshly erased flash memory has the value 0xFF).
Next, enter:
CLEAR 32767
...to confine BASIC to lower memory so that what you load next won't get overwritten. Then type:
LOAD "" CODE
Play the flashutil.tap file. Then type LOAD "" CODE again, and play the flashutilrom.tap file. The first loads at address 57344 (hex 0xE000), and the second at address 32768 (hex 0x8000). Assuming you don't witness the terror of R: Tape loading error, next type:
RANDOMIZE USR 57344
You should now see the following:
Now press Enter, then W. A new menu will appear, with a listing of 16K pages. The flash utility is designed to live in page 4, so press 4. Now the flash utility is in ROM...
The last step put the flash utility in page 4, so it's always there whenever you want to change the contents of ROM pages. Start the flash utility from ZX BASIC by typing:
OUT 31,36
This works from either 48K or 128K BASIC. Note that it copies the flash utility to RAM at address 57344 (and will overwrite anything that's sitting there). Therefore, to accommodate the utility and any ROM images to be flashed, you'll need to lower RAMTOP below 32768 before issuing the OUT command above, otherwise the utility will give you an error message along with an 'M RAMTOP no good error' report.
The flash utility will not work with the Spectrum/Flash jumper set to Flash. This is because this inverts the ROMCS bit (to determine which ROM - the Spectrum's ROM, or page 0 of the flash chip) - so when the flash utility tries to page in a new ROM page, it falls over).
This is important to note in case you feel like invoking the flash utility if you have something like the Gosh Wonderful ZX BASIC ROM in page 0, and have set the jumper to Flash so the Spectrum initializes from this instead of its own ROM.
It probably looks very odd that the flash utility is invoked with OUT 31,36 - rather than RANDOMIZE USR. But there's a method to the madness. Port 31 for output selects the ROM page. 36 is binary 00100100 (or hex 24). So bit 5 is set (which is connected to the ROMCS transistor, so ROMCS is nailed high, paging out the Spectrum's ROM), and flash page 4 is selected.
This happens immediately the moment the Z80 places address 31 on the lower half of the address bus, and 36 on the data bus. So the next instruction it executes will not be the Spectrum ROM's RET instruction to return from the BASIC interpreter's OUT routine, but whatever is in that address in page 4 of the flash ROM. The address in question is 0x1E7F. At this point in page 4, there is a routine that copies the flash utility to RAM, and then jumps to it.
Before you ask, port 31 doesn't conflict with a Kempston joystick - the Kempston interface only responds to an IN 31 instruction. The diags board only responds to an OUT 31 instruction. Therefore, if you have a Kempston interface (that conforms to the Kempston spec and pays attention to the /RD line) that has a through connector, you can load the interface 2 Jetpac cartridge into a flash page and enjoy it with your joystick!
Incidentally, if you program a flash page with the Jetpac IF2 ROM, it can be invoked with an OUT 31, x command from BASIC - and it runs properly. I wonder if Ultimate put valid code in at 0x1E7F just for this very eventuality ... It's probably easier to start ROM games with the flash utility though, so you don't need to work out the proper OUT command!
Next, LOAD "" CODE again, and play the testrom.tap file. Invoke the flash utility with OUT 31,36, and choose W to write a page. Choose page 0. This will write the contents of RAM at address 32768 (which now contain the 48K test ROM) to page 0.
You can now put any ROM image you like in any of the pages. This can be alternative BASIC ROMs, or Interface 2 game ROMs, or other testing ROMs such as the Spectrum 128K memory tester. You need to load them at address 32768. Once a new ROM is loaded, all you need to do to invoke it is to OUT 31,36 - then just press the key corresponding to the page that it is in.
As it stands, the flash utility is extremely simple, and doesn't record what you put where, so just keep a note of it. Next some common tasks you may want to do are listed. Most of these are accessed from the Other Options menu by pressing ENTER from the main menu:
Flash doesn't work like RAM - you can't just arbitrarily change values in memory. It's more like EPROM - you have to erase it before you can change it. For example, if you want to change the ROM image in page 0, so you can boot with a different tester, you will need to erase sector 0 first.
Note that on a 512K chip, each sector is 64K in size, and so covers four 16K pages. This means you'll lose anything in page 1, 2 and 3 as well. (There are solutions - more on that later).
To erase a sector, choose item X from the Other Options menu. Then select the sector you wish to delete. The menu looks like this, and reminds you which pages are affected by the sector erase:
Enter the corresponding key, and the erase operation will start. If you erase sector 1, you'll be asked if you want to keep the flash utility, since this lives in page 4 (which is about to get blown away). If you choose Y here, it will copy the contents of page 4 to RAM (at address 32768), erase sector 1, then reprogram page 4 with the flash utility. You will normally want to press Y, unless you're replacing the flash utility with a new version.
If you need to save the contents of one or more pages in the sector that you want to erase, you need to have some free pages in the flash chip. You can copy the contents of the page to RAM at address 32768, and use the normal programming menu to program a new page with the contents. Do this for as many pages as you need to copy.
There are two ways of setting up a ROM image to be programmed using the Flash Utility. The first method is by LOADing the 16K binary image to location 32768, and then invoking the Flash Utility using OUT 31,36.
The second is to simply invoke the utility, press ENTER from the Other Options menu, then choosing option L to load a 16K image to RAM at address 32768.
The utiliy will prompt you to insert a tape and press play. At this point, you can play the tape or tape image containing your desired ROM image and the utility will load it into memory at the correct location (ignoring any non-CODE blocks, or blocks of incorrect length).
Pressing SPACE or BREAK will abort loading.
The 'w' option on the Other Options menu will write a 16K page. It writes whatever is in RAM at address 32768 and 16K long into the selected flash page. You just need to turn whatever it is you want to write into a TZX or TAP file, which you then play to the Spectrum, loading at address 32768.
The ROM that gets booted if the jumper is set to 'Flash' is whatever is in page 0. You may want to change this at some point, either to update the test ROM designed for this board, or to use some other test ROM image. A suggested method is to keep various test ROMs in other pages, for example having the 48K tester in page 8, and a 128K tester in page 9.
When the need to change the ROM in page 0 arises, the following procedure can be used:
- Erase sector 0
- Use option 'y' from the Other Options menu (Copy a 16K page to RAM) with the desired ROM image.
- Use option 'w' from Other Options menu to program a 16K flash page.