Free PINS on the Cyclone iv in OSSC V1.5?

[renegadeandy]

Hi all,

I am looking for some gpio pins which are not used by the v1.5 ossc as per:

https://www.niksula.hut.fi/~mhiienka/ossc/diy-v1.5/ossc_v1.5-diy_schematic.pdf

Using the Quartus Prime software, specifically the Pin Planner I created a pin finder for 3.3v Assignment == Unassigned, which to me is exactly what I am looking for. It suggests the following pins but the schematic pdf above makes me think they are being used? Am I reading the schematic wrong?

The schematic has labels next to the red arrows and then inside the chip blue pin writing….not sure if the significance of the labels:

6 – ASDO DATA1
8 – nCSO FLASH_nCE
12 – DCLK DCLK
13 – DATA0 DATA0
24 – CLK2
126 – CLK8

Am I free to use any of those pins above?

[renegadeandy]

Any thoughts on this? Does it look right?

[marqs]

You should not use any pins connected to the flash chip. Unused CLK* pins (normally wired to gnd) are free but they can be only used as inputs. Note that SD card DAT1 and DAT2 pins are not used in SPI mode and are already wired to the socket, so those would be the easiest to take advantage of.

[renegadeandy]

Am i right in saying marqs:

6 – input/output
12 – input
13 – input/output
24 – input
126 – input

Are those pins OK? Any others?

[marqs]

Pins 6, 12 and 13 are also connected to flash. You should only use 24,126 (input only) and 28,39 (I/O with 10k pullup).

[renegadeandy]

marqs,

How should I know that I could use those pins, given the schema in my first post and the pin planner in the ossc project, I find it very hard to determine that those pins are indeed free. Pin 28 for example says SD_DAT2 — What does this mean? Why is it there? Should I just ignore that? How am I supposed to know what is what?

[marqs]

My earlier post above explains why SD_DAT1 and SD_DAT2 may be used even though they are connected by default.

[renegadeandy]

Can you answer the specific questions ?

Q1/How should I know that I could use those pins, given the schema in my first post and the pin planner in the ossc project. I find it very hard to determine that those pins are indeed free.

Pin 28 for example says SD_DAT2 — What does this mean? Why is it there? If they are not used in SPI mode, then why are they labelled as in use on the schema? Are you now saying Should I just ignore that? How am I supposed to know what is what?

[marqs]

If you look into RTL (ossc.v) or Quartus compilation log, you’ll notice that SD_DAT[1] and SD_DAT[2] have no drivers in current implementation. Those pins originally were wired to microSD socket so that 4-pin SD mode could possibly be supported in future, but currently SPI mode is good enough for the purpose and there’s no plans to implement SD mode anytime soon.

[renegadeandy]

Hi again

So the SD card functionality uses SPI — which uses 4 signals:

SCLK
MOSI
MISO
SS

Is that correct? Can you help me locate those pin numbers?

I see in the Pin editor:

SD_CLK
SD_CMD
SD_DAT[3]
SD_DAT[2]
SD_DAT[1]
SD_DAT[0]

— how do those tie up the SPI spec?

[marqs]

SD card pinout. SD_DAT[2] are SD_DAT[1] are unused in SPI mode.

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