Simple DSP II

[markseel]

Here's the PCB layout! 

[mhelin]

That looks really nice! Now the question is if the XFLASH tool supports the MRAM for storing the configuration (program code). You maybe have to make own flash configuration file for the tool. How about soldering the BGA device? Guess if you make a stencil for your board it is possible to apply proper amount of solder paste to the BGA pins and by mimicing the reflow soldering process (temps & times) using oven it might be possible to do it at home. For prototyping it might be possible.

[mhelin]

For BGA soldering googled this StencilQuick product, that looks easy to use for prototyping:

http://www.solder.net/products/stencilquik

There are videos showing how to use the stencil, and a free evaluation kit to be ordered. The stencil with adhesive backing is simply left there between the chip and PCB and it keeps the solder paste in place during reflow. The are quite pricey though (about $100 / bag of 10 stencils), maybe suit better for rework (like GPU replacement in laptop mothe borad). There are usual stencils (made of metal) available in ebay which might work but are more difficult to use.

[mhelin]

Regarding the layout it would be nice to have one or two 1-bit ports like XOD35 (A8), XOD24 (B8) or XOD12 (A11)  available on the PCB for things like S/PDIF, ADAT or MIDI interface.

[markseel]

Thanks for the feedback and ideas.  

Now the question is if the XFLASH tool supports the MRAM for storing the configuration (program code).

That's a good point - I'll have to look into it.  The MRAM supports standard SPI FLASH operations so I would bet that the XMOS tool-chain will work.  Like you said, I can always make a new configuration file.

How about soldering the BGA device? Guess if you make a stencil for your board it is possible to apply proper amount of solder paste to the BGA pins and by mimicing the reflow soldering process (temps & times) using oven it might be possible to do it at home. For prototyping it might be possible.

I've not soldered BGA's yet.  But I've seen this kind of rework performed with a heat gun.  That's what I use for parts that have ground slugs/pads on the bottom if the IC package so I think I'll be able to use the head gun to "melt" the BGA package on to the PCB.  Of course I'd rather have the boards assembled but that costs too much in low volume.

[mhelin]

I've not soldered BGA's yet.  But I've seen this kind of rework performed with a heat gun.  That's what I use for parts that have ground slugs/pads on the bottom if the IC package so I think I'll be able to use the head gun to "melt" the BGA package on to the PCB.  Of course I'd rather have the boards assembled but that costs too much in low volume.

OK, so you don't need to add any solder (just flux) when you are soldering a brand new BGA component, only when reworking ("reballing"). SU1 comes with 0.8 mm pitch so it shouldn't be too difficult to place it accurately, and you can use kapton tape to hold the part in position. With hot air station the air velocity should be set very low I guess.

[markseel]

Agreed.  That's the problem I often have - the air velocity moves the part before the solder melts and creates surface tension.  So any suggestions, other than low air velocity, to keep the part stable while heating is valuable.  Maybe I should just look into a hot plate.

[markseel]

Regarding the layout it would be nice to have one or two 1-bit ports like XOD35 (A8), XOD24 (B8) or XOD12 (A11)  available on the PCB for things like S/PDIF, ADAT or MIDI interface.

How's this?

[mhelin]

How's this?

That's great, though the board get little bigger in size, but now it has more uses. Hopefully you can get it working after all those changes 

[mhelin]

The F-RAM used on this board is still quite expensive (though in this case is multifunctional and saves space on board). One of the newest memory technologies is PSRAM (pseudo-SRAM) which is actually DRAM with built-in memory refresh circuit. Haven't found any SPI interface PSRAM yet but if you want really big memory use PSRAM. To serialize the interface it might be possible by using discrete logics, for an example 3x74HC595 for address, 2x74HC595 for writing data and 2x74HC165 to read data (well almost too many chips though those aren't expensive).  XMOS has the SDRAM memory expansion kit for SLICEKIT which takes only 20 pins (http://www.xmos.com/resources/xkits?category=SDRAM+Slice). Wonder how many pins would be needed with PSRAM which doesn't need refresh logics. Using the same interface applied to PSRAM with XS1-L01A-LQ64-C4 part might enable this solution (but then the board size would be bigger and the flash chip would be needed again).

PSRAM chips can be found from Mouser for an example:

http://de.mouser.com/ProductDetail/ISSI/IS66WV51216DBLL-55TLI/?qs=sGAEpiMZZMteY%252blXHTQ5JKR3c313XbVN

This is 1 Mbytes chip (512kx16 bits) and costs 2,21 EUR.

E: looks like for the ISSI PSRAM part the address doesn't have internal latches so three 595's are needed, or you could use three 8-bit latches (CY74FCT2573T) for storing the address. However,the 16-bit data can be read/written in 8-bit chunks (using upper byte/lower byte I/O pins). So you'll need 8 bits for address/data bus, 3 for LE's and  /OE for address latches +/WE, /CS1, /OE, /UB and /LB  for PSRAM. That makes 17 I/O pins, not too many.  Got to see sometimes if my XK-1A could be extended this way. In addition the 1 Mb chip uses only 19 address bits of 24 available, so by adding some address decoding you could easily make  a 512 Mbytes expansion (well, it would cost a lot as you need 512 of those chips but I think there are already larger ones or are coming).

[cloudscapes]

an alternative to serial FRAM is MRAM.

http://ca.mouser.com/ProductDetail/Everspin-Technologies/MR25H40CDC/?qs=sGAEpiMZZMsSm7LhMeloEPcGBwqnPuOP

Also an 8-pin package, fast, serial and retains data without power. It's cheaper than FRAM and you get greater capacity. The downside is that it's a DFN package, so not as easy as SOIC or SOP to mount.

Wish I could find PSRAM much greater than 8MB. Digikey has 64 and 128MB, but they're in BGA.

[mhelin]

an alternative to serial FRAM is MRAM.

http://ca.mouser.com/ProductDetail/Everspin-Technologies/MR25H40CDC/?qs=sGAEpiMZZMsSm7LhMeloEPcGBwqnPuOP

Also an 8-pin package, fast, serial and retains data without power. It's cheaper than FRAM and you get greater capacity. The downside is that it's a DFN package, so not as easy as SOIC or SOP to mount.

Wish I could find PSRAM much greater than 8MB. Digikey has 64 and 128MB, but they're in BGA.

You got me, actually this board uses MRAM not F-RAM as I wrote above. Anyway, the PSRAM is cheap / Mb but is only available as parallel, also the TSOP-44/48 parts are either rare or small.

[mhelin]

The F-RAM used on this board ...

... is actually MRAM.

[cloudscapes]

ah, nice! RAM has been something i've been trying to research quite a bit, for my looper project. still trying to decide whether I should use many expensive serial RAM ics like MRAM, or fewer cheaper parallel ics, but with so many more pins.

great dsp board by the way!