FPGA Replay Board

[freqmax]

The FPGA I/O level depend on the Vcco voltage (asfair) that can vary between 1.2 - 3,3 V. Which voltage that is used depend on the designer (mikej). Any other voltage has to be dealt with using a voltage conversion. The standard trick is a zenerdiode to "Vcc" to limit voltage and a resistor to limit current. The trick has the drawback that it MIGHT overload the supply line that the zenerdiode it's wired to and thus fry most things there (see Xilinx appnote).

A better approach is a dedicated level conversion chip.

[JimS]

The FPGA I/O level depend on the Vcco voltage (asfair) that can vary between 1.2 - 3,3 V. Which voltage that is used depend on the designer (mikej). Any other voltage has to be dealt with using a voltage conversion. The standard trick is a zenerdiode to "Vcc" to limit voltage and a resistor to limit current. The trick has the drawback that it MIGHT overload the supply line that the zenerdiode it's wired to and thus fry most things there (see Xilinx appnote).

A better approach is a dedicated level conversion chip.

I'm going to have to look at the Xilinx site for some of those appnotes. The docs for the simple Spartan 3 dev board I'm looking at mentions the interface problems but doesn't go into much detail on dealing with it. That dedicated chip is going to have to be bidirectional on the parallel port.

[amigadave]

What kind of pinout does that Miracle piano keyboard use really?

If there's pins to do it, then yes. Only the voltage level conversion might need some extra components to deal with. But the question is .. why?
A lot better stuff could be wired via the USB port etc.

I thought from my post the "Why" would be self evident.  For some people the MiniMig and Replay boards, plus the Chameleon and other FPGA based computers that can run an Amiga core, are an alternative to owning an original Amiga, or a new modern replacement for their original Amiga that has died.  Many of those people own peripherals that they once used on their original Amiga computers and might want to use them again on a modern replacement, since the FPGA clones are able to run almost all Amiga software, it would also be good if they could use some of the old Amiga third party hardware expansions, like the Miracle piano keyboard, a DCTV paint and image capture device, and other devices that connected to the Serial, or Parallel ports.

I have a large collection of Amigas that include many such peripherals, so why wouldn't I want to continue using them with these modern Amiga clones?  Of course, if the work to create an equivalent Serial and/or Parallel port for these new FPGA computers is too difficult or costly, then it makes no sense to do it, but if it is relatively easy to do, then why not?

After all, isn't the Amiga community motto, "We did it just because we can"?

Edit:  I have a USB to Parallel port adapter that I bought to run an old large format printer from my Windows PC.  Maybe something like that will also work on the Replay's daughter board (which will have 3 USB ports) to connect devices originally designed to connect to an Amiga Parallel port.  It does not provide the correct 23pin port on it, so another gender changer would be needed to make the connection, which makes the whole experiment harder to accomplish.

[JimS]

Many of those people own peripherals that they once used on their original Amiga computers and might want to use them again on a modern replacement, since the FPGA clones are able to run almost all Amiga software, it would also be good if they could use some of the old Amiga third party hardware expansions, like the Miracle piano keyboard, a DCTV paint and image capture device, and other devices that connected to the Serial, or Parallel ports.

After all, isn't the Amiga community motto, "We did it just because we can"?

I would think the Miracle piano keyboard should work with nothing other than a simple DB9 to DB25 adapter. The trick is whether or not the serial port in the FPGA minimig core can hit the MIDI serial baud rate.

[freqmax]

mentions the interface problems but doesn't go into much detail on dealing with it.

Either use diode to Vcc of correct voltage feed. And use a series resistor to limit current. But make sure to calculate the additional current load on the Vcc such that other devices use more current than the one that will spill over. An additional measure is a zenerdiode from Vcc to GND to sink excess current (Kirchhoff..).

That dedicated chip is going to have to be bidirectional on the parallel port.

The catch with this approach is that you need to tell a bidirectional variant which way signals shall flow.

Many of those people own peripherals that they once used on their original Amiga computers and might want to use them again on a modern replacement, since the FPGA clones are able to run almost all Amiga software, it would also be good if they could use some of the old Amiga third party hardware expansions, like the Miracle piano keyboard, a DCTV paint and image capture device, and other devices that connected to the Serial, or Parallel ports.

The point is that there are usually more efficient ways to accomplish what those peripherals do. Especially using I/O efficient interfaces like I2S etc. That usually also does away with any messy voltage level conversion in massive parallel arrays. Direct connection to the FPGA also imply the risk to fry the main chip.

You can do messy line interfacing and use lots of I/O to connect a sampler. Or you could use a small chip that does it all directly. Just because something is possible doesn't make it the right solution.

Edit:  I have a USB to Parallel port adapter that I bought to run an old large format printer from my Windows PC.

Because USB polls no more than 1000 times /second and each transfer require a lot of setup data on top of being half duplex and hubbed. USB has some really horrible latency times (totaly unsuitable for bit-bang), throughout is way lower than one could expect, and unpredictable I/O performance.
So your USB-to-Parallel port adapter is only good for printers and LED blinking. Unless you have documentation and your willing to write a new firmware for its possible reflashable MCU.

The trick is whether or not the serial port in the FPGA minimig core can hit the MIDI serial baud rate.

Baud is signaling rate, bits per cycle. The bit rate is possible either by dividing some other clock or by using a PLL (DCM). It might require a update to the FPGA binary (core) however.

[psxphill]

Baud is signaling rate, bits per cycle. The bit rate is possible either by dividing some other clock or by using a PLL (DCM). It might require a update to the FPGA binary (core) however.

I'm pretty sure that it would be implemented by a counter clocked by the fundamental frequency, the same as the amiga was. So it should be able to work with any frequencies the amiga did.

[JimS]

The point is that there are usually more efficient ways to accomplish what those peripherals do. Especially using I/O efficient interfaces like I2S etc. That usually also does away with any messy voltage level conversion in massive parallel arrays. Direct connection to the FPGA also imply the risk to fry the main chip.

You can do messy line interfacing and use lots of I/O to connect a sampler. Or you could use a small chip that does it all directly. Just because something is possible doesn't make it the right solution.

Oh, I agree with you totally, it makes a lot more sense to build some new custom hardware replace whatever external devices you might have on the serial & parallel ports. But there is the software involved. If it were relatively easy to do the Amiga's ports, then you wouldn't have to write a new sampler program for example.

Baud is signaling rate, bits per cycle. The bit rate is possible either by dividing some other clock or by using a PLL (DCM). It might require a update to the FPGA binary (core) however.

That's what I meant to say. To drive the Miracle piano, the FPGA core would have to hit the MIDI bit rate. I guess that would depend on the design of that core.

[freqmax]

Oh, I agree with you totally, it makes a lot more sense to build some new custom hardware replace whatever external devices you might have on the serial & parallel ports. But there is the software involved. If it were relatively easy to do the Amiga's ports, then you wouldn't have to write a new sampler program for example.

The action plan depend on how complicated the device is. A simple 8-bit A/D sampler doesn't seem worthwhile for parallel-port replica. While a real-time video compressor might.

Software is not a problem however as the core could translate a new hardware device to behave like the old hardware from a software point of view. And you could have a list of hardware devices to be used that could be selected from the OSD menu.

I can see that I/O will be a problem. So the daughter board connectors P3/P7 would have to be used for a parallel port version. Which would then prevent your 68060/Ethernet etc.. board from being connected that maybe your software requires. And you would be stuffed. A possible workaround is an external CPLD that serialize/parallelize  the connection using the expansion I/O.

That's what I meant to say. To drive the Miracle piano, the FPGA core would have to hit the MIDI bit rate. I guess that would depend on the design of that core.

It depend on which base clocks that is present. Likely the video clock at 27 MHz. If the selected clock is dividable by N is precise enough then a plain logic prescaler will do. Otherwise it depend on I/O availability for another crystal oscillator or availability of DCMs. Finding out these things is one reason why the source for the core is essential.

27 000 000 / 31 250 = 864 divides even!

[JimS]

The action plan depend on how complicated the device is. A simple 8-bit A/D sampler doesn't seem worthwhile for parallel-port replica. While a real-time video compressor might.

I think a better plan would be to imbed a SPI core into the Amiga core, mapped in at some spare I/O address. Then hook on one of those mp3 decoders that interface with SPI and have audio in.

 A possible workaround is an external CPLD that serialize/parallelize  the connection using the expansion I/O.

I like that idea. You could just add something into the Amiga core that was transparent to the Amiga software and at least allow users to print.

[Everblue]

Hey MikeJ any news =)

Got those regulators from customs yet? Thanks!

[mikej]

Hey MikeJ any news =)

Got those regulators from customs yet? Thanks!

UPS have let me down - yet again. Apparently they tried to deliver on Tuesday, having not told me the parcel had been released from customs. They hadn't told the driver the door code. I got a letter today telling me this. Tomorrow is a holiday here, so I won't get it until Monday. grrr.
/MikeJ

[freqmax]

UPS have let me down - yet again. Apparently they tried to deliver on Tuesday, having not told me the parcel had been released from customs. They hadn't told the driver the door code. I got a letter today telling me this. Tomorrow is a holiday here, so I won't get it until Monday. grrr.

UPS is a pain, select another company next time..
Otoh, if the company that placed the transportation order tells them to get their act together. They can get "convinced" and they have delivered on Saturdays before.

So basically.. give them hell.

I think a better plan would be to imbed a SPI core into the Amiga core, mapped in at some spare I/O address. Then hook on one of those mp3 decoders that interface with SPI and have audio in.

Why involve an mp3 decoder?

A/D -> SPI -> FPGA .. core glue.  And you can implement any sampler card every heard of on Amiga.

[Everblue]

UPS have let me down - yet again. Apparently they tried to deliver on Tuesday, having not told me the parcel had been released from customs. They hadn't told the driver the door code. I got a letter today telling me this. Tomorrow is a holiday here, so I won't get it until Monday. grrr.
/MikeJ

Oh well, we've waited years, a bit more wont hurt

[JimS]

Why involve an mp3 decoder?

A/D -> SPI -> FPGA .. core glue.  And you can implement any sampler card every heard of on Amiga.

I suppose so.... is there enough room left in the FPGA to do MP3 decoding?

[ptek]

Hello Mike,

Also what is the prefered method to order a board? PM, email, other? I read from your website that you were making changes into the site. Are you adding shopping support to it?

Do you have any boards available or everything is already promised to future owners?

Thanks

[mikej]

Please send me an email.
Yes, shopping cart is going to happen.
I have boards everywhere at the moment, but I do have a bit of a backlog.
Unfortunately I am going back to China for a week which will delay shipping. I will go and see the factory and make sure more are on the way though, which is good.
/MikeJ