RTL m68k

Is there a "soft core" m68k for FPGAs?

Haveing the cpu in vhdl/verilog would allow to eliminate the need for a special Minimig board. And being able to use plain developer boards from Xilinx or other manufactors.

Have you seen the discussion at Open Cores?

The most finished 68000 in VHDL I know of is from the Atari ST in VHDL: Suska project : 68000 IP v2K7A

Would it make any sense to replace the "FPGA chip + CPU chip" on the current Minimig, with a single-chip "FPGA + CPU chip" device? --DavidCary 21:28, 28 July 2007 (PDT)

---

The Plus Too project is a working hardware replica of the Macintosh Plus and Macintosh 512Ke computers. The project’s goal is to recreate these classic computers using modern electronic components, producing a stand-alone machine able to run period Macintosh software from the mid-1980′s. It replaces the original Motorola 68000 CPU with a soft-CPU module within a FPGA (although a future version will probably use a real 68000 CPU). It replaces the original floppy drives with a SD card interface.

---

The FPGA HP98x6 project includes a 68000 soft core.

---

TobiFlex 070826 13:39
This CPU Core is not finish. The Debuging must go on. Currently hangs up this CPU Core with Kickstartrom 2.04 at #$F81914.

TobiFlex 070826 14:06
I have adapted the minimig Core to the DE2 Board from Terasic with a ALTERA Cyclone 2C35. With an external CPU MC68HC000 runs the Minimig perfekt. I have change the RAM Timing from SRAM to SDRAM - so i can use the on Board SDRAM Chip. And now i use the Board to Debug Wolfgangs 68K Core.

mongo 070826 20:25
Wolfgang's 68K core will run up to about 17 MHz in a Spartan 3.

jkonstan 070826 21:23
external CBT16245 level shifters

TobiFlex 071126 13:49

TobiFlex releases his TG68 MC68000 project source code in VHDL. With a size of 3000 lines.

"The Kernal is 2x-3x faster then the 68000 with the same clock and you can clock them with 28MHz.

I think it is possible to make the minimig 8x-12x faster then the original."

Is there any attempt to make the instruction timings the same as the original 68k?

Most of the byte and word instructions are exact. Long and mulu/divu/rotation instructions are faster.

The MC68EC000 is different from the 68000. I have my Core let run against a real MC68HC000 and can not :find software differences when the Kickstart or some programms are running. So I know all importand :Instructions works correct. About never used Instructions I can not say anything.

Example: I have found no program for the AMIGA that use CHK or MOVEP Instructions.

About the doc on the second link. My Core use no prefetch. My Core use classical Fetch/Execute last - :Decode - Fetch next/Execute - order.

Thats why most Instrucions can execute in 2 clocks. The Bus wrapper expand this to 4 clocks.

But for the minimig is the prefetch not so important. The core is fast enough to decode the opcode between as=high. So the timing is the same as the 68000 timing.

On my DE2 Board with a real MC68EC000 and running ANARCHY1 DEMO I can see some rendering error but with the softcore I can not.

I dont know what happens but I think my core has a high Betatested Level. (Upss I hope you can understood my - sorry for my poor english)

OPCODE 0x0F0E MOVEP.W ..... My Validator stop here.

Boards:

http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&No=83

http://www.altera.com/products/devkits/altera/kit-cyc2-2C20N.html

billt 071126 15:57

Simulators

http://www.symphonyeda.com/proddownloads.htm

http://ghdl.free.fr/

http://freehdl.seul.org/

alexh 071126 16:14

There are some subtle undocumented 68k behaviour that you might be interested in:

http://www.trzy.org/files/68knotes.txt

http://pasti.fxatari.com/68kdocs/

Testdisc known to be sensitive to 68000 incompatibility: http://amiga.nvg.org/warlock/adf/b/Birk+Sundell/100C64Tunes.adf.gz

Dennis 071126 19:48

Quick compile using webpack 6.3.03i:

Device utilization summary:

---------------------------

Selected Device : 3s400pq208-4

Number of Slices: 2627 out of 3584 73%

Number of Slice Flip Flops: 1052 out of 7168 14%

Number of 4 input LUTs: 4841 out of 7168 67%

Number of bonded IOBs: 74 out of 141 52%

Number of GCLKs: 1 out of 8 12%

=========================================================================

TIMING REPORT

NOTE: THESE TIMING NUMBERS ARE ONLY A SYNTHESIS ESTIMATE. FOR ACCURATE TIMING INFORMATION PLEASE REFER TO THE TRACE REPORT GENERATED AFTER PLACE-and-ROUTE.

Timing Summary:

---------------

Speed Grade: -4

Minimum period: 39.906ns (Maximum Frequency: 25.059MHz)

Minimum input arrival time before clock: 16.900ns

Maximum output required time after clock: 16.576ns

Maximum combinational path delay: No path found

I need a bigger FPGA :-)

karsten 071126 20:02

Days of Thunder uses the CHK instruction: http://eab.abime.net/showthread.php?t=1144