Newbie question: where are the high-i/o boards ?
Posted: Fri Aug 24, 2012 9:59 pm
So, having looked at the XMOS, it seems pretty cool, and well worth getting to know. I was looking at the G4, and that would seem to have 4 cores, each with 64 i/o on them, for a total of 256 i/o. That's a lot of i/o :)
What's not obvious is if you can actually get a (cheap :) dev-board that exposes all these wonderful i/o ports. The best option I can find seems to be the XC-2, but that only has 84 i/o pins - I realise that some are lost to the ethernet, XTAG, whatever, but seriously, where's the rest of the pins gone ?
What I'd like to do is put a video-decoder, 2x1MB SRAM chips, and an ethernet device (amongst other things like ADC, flash, etc.) on the board. I don't expect to find a board like this, but ideally I'd be able to find a board that exposed sufficient pins that I could plug in the missing bits.
Ideally, of course, we'd get a card (Best would be DDR2 SDRAM DIMM which'd give 240 pins, but I'd settle for a x16 PCIe card which'd give ~160 pins) that we could plug into a "motherboard" with a standard mating socket. If you really want to go for it, something like http://www.enterpoint.co.uk/moelbryn/darnaw1.html gives you an ideal solution - an easy re-usable prototyping board with some useful on-board things (memory, clock, SPI flash,...) that you can plug into your personal "motherboard" and let rip... The Darnaw1 isn't even too expensive, at £95.
[Edit]
To give you an idea of what I mean regarding the PCIe card slot idea, attached is one I did for the Atmel AVR chip - all the port lines are available on every slot, as well as CLK (@20MHz, this works surprisingly well :), GND, 5v, 3.3v and Vin (normally 9-12v). This is using PCIe 1x, but with the larger number of ports on an XMOS, we'd need the larger-sized slot. It's simple, but very flexible. I have a number of boards (SRAM, ethernet, switches, LEDs, LCD, Serial port, ...) that slot into the PCIe slots and do whatever I want - all I have to do is make sure I design the slot-boards to not conflict. I had plenty of i/o per socket so I used some of the spare lines to identify which slot the board was in. I figured it might come in useful someday [grin].
In the photo, the board on the left is power, the middle is serial/SPI flash, and the right is the CPU. The "motherboard" is a completely passive backplane.
Oh yeah, the serial/flash board has header switches (yellow) to enable/disable the serial port connection and the flash SPI connection. If the header switches aren't in the closed position, those components are isolated from the backplane. It's infuriating to me when I need "just one more i/o" as I stare at the LED that the board designer "thoughtfully" hardwired to a port line. Make it possible to isolate the LED and provide me the port as an i/o already! Grrr.
[/Edit]
So, am I missing something? Am I dreaming? Or is it a case of "here's the tools, mate, off you go" ? :)
Please don't take this the wrong way, the xmos looks like its going to be really fun to work with, but too many times in the past, I've bought a dev-board thinking "this is going to be fine", and later realised I'm short of <insert X here>. The for-sale boards seem to be pin-restricted, so if there's other (affordable, I don't want to pay $1k for the XDK XS1-G!) options, I'm all-ears :)
Cheers
Simon
What's not obvious is if you can actually get a (cheap :) dev-board that exposes all these wonderful i/o ports. The best option I can find seems to be the XC-2, but that only has 84 i/o pins - I realise that some are lost to the ethernet, XTAG, whatever, but seriously, where's the rest of the pins gone ?
What I'd like to do is put a video-decoder, 2x1MB SRAM chips, and an ethernet device (amongst other things like ADC, flash, etc.) on the board. I don't expect to find a board like this, but ideally I'd be able to find a board that exposed sufficient pins that I could plug in the missing bits.
Ideally, of course, we'd get a card (Best would be DDR2 SDRAM DIMM which'd give 240 pins, but I'd settle for a x16 PCIe card which'd give ~160 pins) that we could plug into a "motherboard" with a standard mating socket. If you really want to go for it, something like http://www.enterpoint.co.uk/moelbryn/darnaw1.html gives you an ideal solution - an easy re-usable prototyping board with some useful on-board things (memory, clock, SPI flash,...) that you can plug into your personal "motherboard" and let rip... The Darnaw1 isn't even too expensive, at £95.
[Edit]
To give you an idea of what I mean regarding the PCIe card slot idea, attached is one I did for the Atmel AVR chip - all the port lines are available on every slot, as well as CLK (@20MHz, this works surprisingly well :), GND, 5v, 3.3v and Vin (normally 9-12v). This is using PCIe 1x, but with the larger number of ports on an XMOS, we'd need the larger-sized slot. It's simple, but very flexible. I have a number of boards (SRAM, ethernet, switches, LEDs, LCD, Serial port, ...) that slot into the PCIe slots and do whatever I want - all I have to do is make sure I design the slot-boards to not conflict. I had plenty of i/o per socket so I used some of the spare lines to identify which slot the board was in. I figured it might come in useful someday [grin].
In the photo, the board on the left is power, the middle is serial/SPI flash, and the right is the CPU. The "motherboard" is a completely passive backplane.
Oh yeah, the serial/flash board has header switches (yellow) to enable/disable the serial port connection and the flash SPI connection. If the header switches aren't in the closed position, those components are isolated from the backplane. It's infuriating to me when I need "just one more i/o" as I stare at the LED that the board designer "thoughtfully" hardwired to a port line. Make it possible to isolate the LED and provide me the port as an i/o already! Grrr.
[/Edit]
So, am I missing something? Am I dreaming? Or is it a case of "here's the tools, mate, off you go" ? :)
Please don't take this the wrong way, the xmos looks like its going to be really fun to work with, but too many times in the past, I've bought a dev-board thinking "this is going to be fine", and later realised I'm short of <insert X here>. The for-sale boards seem to be pin-restricted, so if there's other (affordable, I don't want to pay $1k for the XDK XS1-G!) options, I'm all-ears :)
Cheers
Simon