Category Archives: FPGA

Items relating to FPGA development

More PACE adventures

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After I ported the Pacman core to the Chameleon 64 last week, Mark McDougall suggested that Moon Patrol would be a good project to port next, so that’s exactly what I’ve done.

mpatrol

I’ve also improved the Pacman port somewhat, cleaned up the clocking arrangments (now I have a clearer idea of how they’re supposed to work) and integrated the Chameleon_CDTV entity, which means the CDTV infra-red controller can now be used.

I’ve also ported Moon Patrol to the MiST board, and to my Frankensteined C3 board.

The downside of Moon Patrol is that it requires a two-button controller, since one is used for fire and the other for jump.

Binaries for the Chameleon64 can be found here, while a patch against current PACE SVN can be found here.

Pacman on the Chameleon 64!

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Having seen the PACE project’s Pacman core running on the MiST board, I wanted to try and get it running on the Chameleon. This task is made much easier by the existence of Peter Wendrich’s Chameleon_io entity, which abstracts away the messy details of reading the C64’s or Docking Station’s joystick ports.

This is just a quick-and-dirty port, but should be playable. The coin switch is mapped to the leftmost button on the Chameleon, while the start button is the middle button.
To play, you’ll need a joystick in C64 port 1, or attached to the docking station. (So far I’ve only tested with a real C64.)

The core can be found here.

Source code (in patch form against today’s PACE SVN) can be found here. Because I used Till Harbaum’s port to the MiST board as a starting point the patch adds support for his board as well, and also my Cyclone-3-board-from-EBay.

Trials, Tribulations and Toolchains

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Edit: Future me, nearly 10 years later, says don’t bother attempting these steps unless you really have no alternative. My comment below about guides found on the net quickly becoming obsolete now applies to this post!

If you’re using Ubuntu or a derivative, then the arm-none-eabi-… toolchain is now in the repos, so can easily be installed with apt, and there’s even an m68k gcc cross compiler too.

<Historical content resumes…>

To build the OSD firmware for the Minimig projects, a cross-compilation environment is needed. Configuring GCC for this task can be an arcane process, and aspects tend to change from time to time, so guides found on the net quickly become obsolete. For instance, guides recommending the target “arm-elf” will fail with the latest GCC. Instead we need to use the target “arm-none-eabi”.

Here’s how I built a toolchain for building both M68K (Chameleon Minimig port) and ARM (Original Minimig and MiST) versions of the firmware:
Continue reading →

>>>>>>Acceleration!

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Following on from the addition of the Two Way Cache in my last post, I’ve made some more speed improvements to the Chameleon 64’s Minimig core.

Firstly, I’ve added a single-word write buffer, which means when the CPU writes to Fast RAM it doesn’t have to wait for the write to complete.  Provided completing the write takes priority over any potential reads from the same address, and the Cache is updated to reflect the new data, then the CPU can continue merrily processing.

Secondly, I’ve added a second access slot to the SDRAM controller, which means in many cases the wait for RAM service is reduced from a worst-case 24 cycles to 17 cycles.  The downside is that because RAM operations between the two access slots overlap, they can’t be to the same RAM bank.  For this reason I’ve remapped the RAM so that bank 0 contains Chip RAM, Slow RAM, Kickstart ROM and OSD RAM, leaving banks 1-3 free for Fast RAM.  Chip RAM and Kickstart ROM accesses can thus now overlap with Fast RAM accesses.

Finally, I’ve simplified the TG68 wrapper so that it no longer uses the enaWRreg signal to synchronize the CPU to the Amiga’s 28MHz clock.

Between them these changes give an average speed increase of about 65%. Continue reading →

Experimenting with TG68

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Part 12b – a better cache

I’ve *finally* found the subtle bug that was causing my two-way cache to fail.  The symptom was that the boot process would appear to work fine, loading an S Record off the SD card, but having loaded it, the code would fail to start.  It was as though the bootloader was ignoring the S9 record at the end of the firmware file.

After various fruitless attempts to track this down, and to construct artificial testcases to trigger the behaviour, I finally added some serial debugging breadcrumbs to the first-stage bootloader.  From this I found that the final S9 record was being treated as thought it were an S1! Continue reading →

Experimenting with TG68

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Part 12a – a better cache

The TG68MiniSOC project has so far used a very simple cache for the CPU.  The SDRAM controller is set up to use four-word bursts, so the cache simply stores each complete burst.  Under this scheme, when data is read sequentially from RAM, only one read in four will need to wait for the SDRAM controller.  This is the simplest possible example of a Direct Mapped cache, with just a single cacheline. Continue reading →

DB9s and Matrix Board

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One thing I’ve always found annoying when working with DB9s is that the staggered pins makes them incompatible with matrix board.  The simplest solution has always been to just put the DB9 on the end of a cable, and either solder the cable directly to the board, or use a box header, which has parallel rows of pins.

A few days ago I was hit with a flash of inspiration – and now I can’t believe I didn’t think of this solution sooner! Continue reading →

Slow progress, but progress nonetheless!

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I’ve recently pushed some changed to the TG68MiniSOC Github repo at https://github.com/robinsonb5/TG68_MiniSOC.  Changes this time round include:

  • increasing the system clock frequency to 133MHz.  In order to do this I had to add some wait states to the processor, but the increase in RAM bandwidth makes it worthwhile.
  • Adding some more robust filtering to the PS/2 clock signals.  At the faster clock speed I was finding that the mouse and keyboard were misbehaving – it appeared as though there were spurious clock edges causing the receiver to get a bit or two out of sync with the keyboard and mouse.  After trying various tweaks to the PS/2 module’s parameters with no success, I tried running the PS/2 clock signals through the debouncer I mentioned in the post about latching power circuits – and that seems to work like a charm.
  • Since two of the target platforms have 32 meg of RAM, and since I now have a Platform Specific register the firmware can read to query how much RAM is present, I’ve moved the base address of the hardware registers.  Previously they were at 0x800000, which is 8 megabytes into the address space.  This works out nicely on the DE1 which only has 8 meg of RAM, but on the Chameleon and CIII board the base address needs to be above 32 meg.  So I’ve changed it to 0x80000000 – or 2GB.  Chances are I’m not going to encounter an FPGA dev board with more than 2 gig of RAM! Continue reading →

Experimenting with TG68

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Part 11 – porting to the Turbo Chameleon 64

After porting the Minimig core to my ebay-acquired Cyclone III board, I’ve spent some time this week porting the MiniSOC project to the Turbo Chameleon 64.

Hardware-wise the TC64 is very similar to the CIII board – the FPGA is identical, and there’s the same amount of SDRAM – albeit with a slightly different layout – so porting projects from one to the other is fairly straightforward.  The only complicated part is routing certain signals through a CPLD which is used in the TC64 to multiplex some of the IOs, and as a bonus, to provide 5v tolerance.  This is taken care of in the Chameleon-specific toplevel, meaning once again that the same basic source tree can be built for DE1, the CIII board and now also the Turbo Chameleon 64. Continue reading →