FPGA   II

Hi Henk.

Well, after some 7 weeks delay waiting for a new FPGA board, I have got theball rolling again. The colour palettes and video addressing are correct,graphics modes are programmable. So I think that I can pronounce that I havea Atom that is fully working as regards being able to type programs in andrun them!

Okay, the sound buzzer may not be working, and I have not bothered with thetape interface (because it needs a lot of analogue filtering circuit!).

I always thought it was pretty lame that the Atom had to scroll the screenby moving every screen byte. This is okay for the small screen and there isnot much point scrolling the screen faster than they eye can follow.However, it would be nice to have the screen start address programmable.

made it so you can say A=#8000 (default after reset) or wherever you wantthe screen RAM to be, then !#BE00=A.
I wrote a small program to set a graphics mode and keep incrementing thestart by 32 bytes (1 scan line). This has the desired effect! It scrolls thescreen through 64K RAM. You can even see the system variables changing whenit covers that RAM area!
It only accesses the RAM space, so you cannot 'view' the ROM or I/O. I thinkthis is right because viewing the ROM is not very useful, and reading theI/O would disturb the correct behaviour of some I/O chips.
As I type this email I am watching a graphic screen scroll rapidly, inBASIC.
Changing the start address effectively scrolls the entire screen (6 to 8K)instantly!
At one scan line per field (1/50 s) this would scroll 8K in 5s, 64K in 40s.But of course you can also do 'flicker book' type animation, swapping theentire screen 50 times per second.
I am going to modify it so the screen 'window' stays inside a block of 2^nbytes (I think 8K is right for the highest screen resolution) and not end uphaving screen overwriting other areas!
I am feeling very happy with my success, and am off to open a bottle!

Een mailtje later meldde hij o.m. nog het volgende:

The OS assumes the display is always at 8000h, nomatter what my display controller does. To take advantage of this newfeature, one has to write new software and perhaps modify the old OS.Eventually I will need to write a program to demo the new features!Something with scrolling, graphics, music, etc?
I have started adding more I/O registers in preparation for connecting themto various programmable things.
A serial port sounds a good idea, to load programs more conveniently thantape!

Op 24 april volgde het onderstaande bericht:

I have recently got my atom downloading text from the PC printer port at about 64 kbytes / second overhead (i.e. just discarding the data). If you echo the bytes to screen it falls to about 1K / second.
Still, it lets me type programs in PC text files and get them in the Atom without further typing!

Right now, the firmware is compiled in. I will need more for bigger projects. So I need to either fit the flash ROM chip, or have it boot from a compact flash card.
I think the Flash ROM chip is the least difficult. At least from a mechanical assembly point, because it is already wired up and ready. I want to keep as many pins as possible free for future ideas ;-)

Tot zover het nieuws van het FPGA front. OP zijn website is meer over dit onderwerp te lezen.
Kopieer één van de onderstaande links in uw browser:

http://www.howell1964.freeserve.co.uk/logic/acorn_atom_project.htm
http://www.howell1964.freeserve.co.uk/logic/acorn_atom_lpt.htm