OCM: questions and answers

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Van cax

Prophet (3738)

afbeelding van cax

28-12-2006, 16:44

Is there any versioning scheme, and how the version number of the FPGA code OCM runs can be retrieved ?

Van Tanni

Hero (556)

afbeelding van Tanni

28-12-2006, 18:01

I amp trying to compile the code for the spartan 3 witrh xilionx ise
free edition but there are syntax errors in the code !
I believe the compiler from xilinx does not behaves the same way
as the altera one.
Of course I already replaced the altera specific device like the frequency synthesiser with a xilinxi DCM block, it is really syntaxic errors
especially on arrays and type of array declaration for the opll.
I may give a try disconnecting the opll ...

Leo, can you post the errormessages and the associated lines of code, if it isn't too much. Or at least one or two exemples?

Van Tanni

Hero (556)

afbeelding van Tanni

28-12-2006, 18:54

Maybe the errors occur due to your use of VHDL'87 instead of VHDL'93 standard?

Van tcdev

Expert (76)

afbeelding van tcdev

18-02-2007, 02:33

To answer some questions:

There is no USB chip on the board - the USB differential I/O lines are connected directly to the FPGA. This means that, in theory, either USB master or slave functionality can be added to the OCM. In practise however, I doubt that either would actually fit into the EP1C12 with the OCM - it's already 83% logic utilisation IIRC - getting close to the upper limit for 'real-world' designs without spending hundreds of hours manually fitting the design. But maybe a slave mode would fit?

Yes, FPGAs do allow instantiation of SRAM blocks. However, they're not persistent as someone suggested. IIRC the EP1C12 has around 27kB of block RAM in it. The OCM is using only 30% atm.

The input clock to the OCM is 21.48 MHz - chosen to be CPU/video-friendly. An internal PLL produces another couple of 85.92MHz clocks for the SDRAM. There are also several gated clocks used throughout the design that are derived from the 21M clock, including the CPU, which is 1/6 21M. The design changes this divisor for faster CPU speeds. The upper limit is determined by how "fast" the design can be fitted by Quartus, which depends on the complexity of the logic and the physical limitations of the EP1C12.

The VDP clock is completely independent of the cpu clock and is fixed at 21.48MHz. This is necessary because it is the base clock used for video generation and also the system clock that interleaves access to SDRAM by the CPU/VDU etc. At the very least, the CPU needs to be an integral division of the VDP clock - without a major rewrite of the design.

FWIW the bulk of the design is in the VDP and sound chips. For some reason the YM2413 is referred to as VM2413 in the source. The Z80 core is the T80 core from opencores - and it's *not* the latest version so it'll have a bug or two.

Atm I'm porting the design to my own hardware and can see the OSD on the VGA output. I'm having trouble understanding how the BIOS/BASIC ROMs are bootstrapped by the design, which has a 512-byte IPL rom embedded in the FPGA.

Hope this sheds some light.
Regards,
Mark

Van karloch

Prophet (2157)

afbeelding van karloch

18-02-2007, 21:39

Interesting info tcdev, thanks for sharing it Smile

Van Akul

Rookie (20)

afbeelding van Akul

19-02-2007, 13:53

The Japanese version of OCM have a 110/220V AC power supply like the Bazix/European version?? or only works on 110? Pardon for my English.

Van Alex

Master (205)

afbeelding van Alex

19-02-2007, 21:44

The Japanese version of OCM have a 110/220V AC power supply like the Bazix/European version?? or only works on 110? Pardon for my English.

The Japanese version has a universal (100-240V, 50/60Hz) power supply. Though, it comes with a Japanese plug. In Europe you must use an adapter plug to plug it into the socket. Don't know about countries in other parts of the world.

Van Akul

Rookie (20)

afbeelding van Akul

19-02-2007, 22:13

Thanks Alex.

Van timbr

Resident (43)

afbeelding van timbr

22-02-2007, 18:22


Atm I'm porting the design to my own hardware and can see the OSD on the VGA output. I'm having trouble understanding how the BIOS/BASIC ROMs are bootstrapped by the design, which has a 512-byte IPL rom embedded in the FPGA.

I'm busy myself porting the thing to my old Altera-Apex development board. I allready have it running, without having to modify the IPL rom. But because I was curious wat it does, I disassembled it and had a look at it. Although I have quite some Z80 experience I did not succeed in understanding it within the time I was willing to spend at that moment. But maybe you are interested in the disassembled code (including assembler to reproduce the exact same binary):
http://home.versatel.nl/timmarianne/ipl_rom.zip

Van snout

Ascended (15187)

afbeelding van snout

22-02-2007, 18:39

For those wondering: the adapter with the OCM can be used in USA, UK and JP. The Bazix edition contains an extra adapter allowing you to use it in most/all European countries as well.

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