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Defining adv7513 resource for a new board with subsignals different from DE10-Nano #122

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asumagic opened this issue Nov 14, 2020 · 2 comments
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Defining adv7513 resource for a new board with subsignals different from DE10-Nano #122

asumagic opened this issue Nov 14, 2020 · 2 comments
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@asumagic
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While implementing a board file for the Cyclone V GX starter kit, I noticed that it uses the same HDMI transmitter as the DE10-Nano as defined here.

The pin names are identical, but the GX starter kit does not have audio related pins wired in. Specifically, these are missing:

  • HDMI_I2S0 (i2s0)
  • HDMI_MCLK (mclk)
  • HDMI_LRCLK (lrclk)
  • HDMI_SCLK (sclk)

I'm assuming that resources under a certain name (in this case "adv7513") should keep consistent subsignals across multiple boards. How should I handle this?

Furthermore, the DE10-Nano dedicates pins for the adv7513 I2C, like so:

            Subsignal("scl", Pins("U10", dir="o")),
            Subsignal("sda", Pins("AA4", dir="io")),

In the GX starter kit, this is not the case, as the I2C_SCL (PIN_B7) and I2C_SDA (PIN_G11) pins are used for the programmable oscillator, the audio interface, among other things, i.e. should be reused across several resources.
Since defining multiple identical pins assignments or otherwise reusing pins appears to be impossible, how should I proceed?
@whitequark
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Good question. There is such a thing as "optional pins"; I/O cores may use hasattr and friends to check if they e.g. have I2S related pins. This is not ideal, but this transmitter is a very niche device, so I believe it would be OK to simply omit them for now.

@whitequark
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Actually, scratch that. It turns out we already decided to split the HDMI transmitter into several resources in https://github.com/nmigen/nmigen-boards/pull/119/files#diff-9717074072a7b3688a96b0364849e30ef11cec472ab601e4733d1f2b7205bbf2R24-R46. I think DE10-nano and the Cyclone V starter kit should follow the example of that board, then.

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@whitequark @asumagic