FPGAARCADE minimig compatible board, comments?

[mikej]

There is going to be another update.

Originally for hard disk usage I was going to use an IDE connector and either hard disk or CF disk on the daughter card. It would be a great feature to have hardfile support from the SD card for the base platform. The AVR SPI transfer speed in this case is limited to about 300KBytes per second. This is ok for floppy and booting, but not great.

So, I am going to add a multiplexer which lets the FPGA master the SD card directly. The AVR will still contain the knowledge of the file system and talk over the current SPI link to the FPGA. The FPGA will then enable it's second SPI interface (reusing the 4 IO programming pins which conveniently already go to the AVR part of the PCB) and take over the job. Depending on the SD card we should get transfer speeds of several MBytes per second. This will delay the board a week or so.
so comments can still change things
/Mike

[mikej]

While I am changing the SPI routing, Jakub has convinced me to replace the AVR with the ARM7S chip he uses for the hardfile demo. Amazingly, the cost of the chip and the USB socket is the same as the AVR. I have managed to fit all on the PCB, just need to fix the routing (again).

The main benefit is I can pick up Jakub's work for hardfile support, which save time. It also goes faster, and we have gained a USB port for flashing the microcontroller - and we can potentially use the USB port from the FPGA.

Updated schematics and layout in a few days. Assembly pushed back two weeks.

/Mike

[mikej]

At the moment there are too many variables to get an exact pricing, I am waiting for some more quotes. The aim is less than 200E for boards from the initial small run. Production boards should be significantly cheaper. There are a few options for suppliers, but initially they can be ordered through me.

Best,
Mike.

[mikej]

Latest ARM schematics and layout update.
www.FPGAArcade.com

right, this is it, no more changes....

[mikej]

For those interested I have posted pictures of the Replay board PCB I have just brought back from China.

www.fpgaarcade.com

I will get the boards built this week, but it will take a little while before we have the system up and running.

/Mike

[mikej]

Board is complete and initial testing is going well.
Power supplies, FPGA and ARM controller all working ok.
/Mike

[mikej]

"Great news. What sort of transfer speeds are you getting from the hard file, better than on the Minimig v1.1 or the same?"

Thanks. Not there yet, I'll keep you posted.

[mikej]

The ARM is now booting and mounting the SD card file system. I hope to have some performance numbers soon.
/MikeJ
www.fpgaarcade.com

[mikej]

yes, in principle, but it is not something I will be doing.
It is much more convenient to drop it into a modern, smaller, mini-itx case.

The modern interfaces like USB and Ethernet also would not fit easily into the old cases.

/Mike

[mikej]

They only come assembled and fully tested, it's not really possible to home build.
/Mike

[mikej]

Hi,
No, the power supplies seem exceptionally stable thankfully.

The only slight issue is that before the FPGA / CPU are configured the LEDs come on at low brightness due to the internal pull ups. I should have wired them to VCC not GND to avoid this. Perhaps this can be considered a "not configured" feature

I am doing the small daughter board now. The composite / SVHS out is driven from a coder chip and is fed from the front small expansion connector which carries video and audio. I should have the PCB finished today. I am doing a 68000 and 68020 daughter board as well to speed up testing of the soft cores.

/Mike

[mikej]

I expect the DDR terminator and all the resistors can be not fitted on the production board to save cost. I'll see what it does to the memory timing window.

The board will be v1.0 when it is released to production.

I have a 68030 on my desk but it is a huge PGA version.... The 68020 is needed to get the A1200 core up and running.
/Mike

[mikej]

yes, this is what R86 is doing on the 2V5 rail - providing some load. Some of the configuration pins are 2V5, current limited with a resistor but driven from a 3V3 source. You get some leakage through the IO cell protection diodes which try and raise the 2V5 supply. Most DC-DC converters can only source, not sync current (that's why I use a linear for VTT) so your 2V5 gets driven upwards...

/Mike

[mikej]

On a slightly different subject I'm just finishing the top mini break out card which has two front mounted joystick ports, composite and SVHS out and two audio RCA connectors.

At the moment the audio connectors are directly connected to the stereo jack out on the main board. I could add an output buffer / filter to these but I would have to either use a single ended op-amp and another output capacitor (not good) or generate a local -ve 5V supply. Any suggestions? worth the hassle / cost? The DAC data sheet is here :

http://www.wolfsonmicro.com/uploads/documents/en/WM8729.pdf

p.s. Does anybody have a 68EC020 processor I can buy / have? A broken A1200 main board would be a good donor if the processor is good.
/Mike

[mikej]

Thanks,
There are a few switching inverters which will do the job, but most are switched cap. Even if the switching frequency is quite high the supply will need some extensive filtering.

The DAC has quite a good build in filter, so is there any benefit in adding a line driver - especially if the op-amps power supply is not the best?
/Mike

[mikej]

At the moment the DAC output is capacitive coupled directly to the stereo jack - which is the cheapest and smallest solution for the main card. The DAC has an output filter so it will work fine.

I have more space on the breakout board, and Wolfson talk about an optional low pass filter. It would also have low output impedance good for driving long cable runs.

Downsides are the cost (small) and the need to produce a -ve supply. It can be done with an inverting reg but they are a bit noisy, so without going overboard with the filtering the buffer may not improve the quality of the output, which is the aim for this optional card.

Thoughts?

/Mike