alexh wrote:
Any board that can take one crystal and produce selectable NTSC and PAL clocks it's going to work.
Finding that single crystal and the settings for the clock synthesiser will be the actual research.
STB boxes use just one crystal to generate PAL and NTSC clocks so the solution is out there. The capabilities of the Altera equivalent of the Xilinx DCM (Digital Clock Module) would also have to be looked into (work that I am sure Tobiflex and the other DE-1 users have already done)
Okay, so lets start looking at the frequencies we need. First, I need some clarification on the differences between PAL and NTSC Amigas. According to this webpage,
http://www.mjmwired.net/kernel/Documentation/m68k/README.buddha, NTSC Amiga clock oscillates at 28.37516Mhz, just off the NTSC frequency of 28.63636Mhz. From this base frequency the clock speed is divided to obtain all the different frequencies it needs to produce, if this is right:
http://blogs.msdn.com/oldnewthing/archive/2004/12/02/273721.aspx"The early Amigas had a similar arrangement. The oscillator runs at ~28 MHz, the pixel clock runs at half or a quarter of that depending on screen mode, the processor runs at a quarter of that, the memory bus runs at an eighth, the colour clock runs at some other fraction I don't remember, and the "E-clock" used by 6800-style chips runs at a fourtieth. The programmable timers are in two VIA chips connected to the E-clock and the OS sets one of them to a sensible 1/50 second (or the best approximation it can manage, anyway). A lot of regular interrupt handlers are connected to the vertical blank interrupt, though, making them dependent on the screen mode. Some people made the mistake of using that for music play-routines."
When it comes to the PAL clock signal, am I right in thinking the same oscillator was used, but the PAL versions of Agnus produced the frequencies needed?
http://en.wikipedia.org/wiki/MOS_Technology_Agnus PAL video frequency (for reference):
http://lipas.uwasa.fi/~f76998/video/modes/"For example, the designers of the Commodore Amiga line of computers chose to use a pixel clock of 70 ns for some of the graphics modes. (70 ns = 70 × -10-9 s = 1 / (70 × 10-9) Hz = approximately 14.286 MHz sampling rate)."
Dennis, one point I'd like to ask you. On this Minimig webpage,
http://home.hetnet.nl/~weeren001/minimig.html, you say that the Minimig clock frequency (in current design) is 7.09379MHz, derived from a 4.433619MHz crystal. As this isn't a whole number multiple (close to 1.6, but not spot on), I was wondering whether the current crystal could create NTSC frequencies (if not, why not)? Thanks in advance.
mrmkl wrote:
Must it have actual IDE emulation? (WHDload require it?) If it is only needed to mount a hardfile image, you could load any driver from a bootable floppy image, perhaps create a mountlist file from the RDB-header of a hard disk image, mount partitions with the appropriate filesystems, and continue the boot process from the mounted partition.
Maybe you could even DMA the data stream to RAM, for speed-up?
mrmkl, I don't understand what you are proposing here. Are you proposing booting a file that describes a filesystem structure?
