Sunday, August 11


Daily News Stuff 10 August 2019

Late Final Extra Edition

Tech News

  • The feud between Japan and South Korea has settled down a bit with Japan approving shipments of chemicals for chip fabrication.  (AnandTech)

    I know why there are lingering tensions, but there's almost no-one left alive from when that stuff happened, so maybe cool it, guys?

  • Samsung has announced its own PCIe 4.0 SSD.  (Tom's Hardware)

    This one goes up to 8GB per second - but that's the version that uses a x8 PCIe slot, not M.2.

  • Arm and Global Foundries are partnering on a new 3D chip design.  (Tom's Hardware)

    That is, not a chip that renders 3D graphics, but a chip that is itself built in three dimensions.  Global Foundries process allows a million interconnects between layers per square millimetre.  That's rather a lot.  On a circuit board you might get one.

  • 2019 sucks for smartphones.  (ZDNet)

    Apple is a fashion company, not a tech company.  Samsung wants to be a fashion company.  And Huawei has found there's a downside to being a subsidiary of the Chinese military.

    Xiaomi and Oppo and other smaller players haven't been doing so badly though.

Retrocomputing Journal

I've started work on the circuit design for the A750, and the first step in that is nailing down the pinout for the H750 at its core.

Unlike traditional CPUs like the Z80, where each pin had a well-defined function, each pin on a modern microcontroller like the H750 can be configured to perform multiple different tasks: Act as a timer trigger, send I2C serial data, feed an analog-to-digital converter, or be a simple output pin switched on or off by software.

In the H750, each pin can have up to 16 pre-defined functions, only one of which can be active at any given time.  While they're configured by software, they also have to be reflected in your circuit design.  If you change an ADC input into a QSPI clock while the analog signal is still coming in, it's not going to work terribly well.

The reason this matters is that you can't route any signal to any pin the way you can with an FPGA.  You have some choice, but it's not completely free.  And as it turns out, the function-to-pin mappings in the TQFP-100 version of the STM32H750 are a doubly-indirect dog's breakfast.

I mentioned the idea of using the camera input as a screen capture device.  That's impossible on this version of the chip: The camera input uses the same pins as the LCD output.

Worse, Ethernet and QSPI, both functions I need, steal critical pins from the LCD controller.  You weren't using the third bit of the R part of RGB, were you?  Oh, oops.

It's possible to work around this in indexed colour modes - that is, display modes where (for example) you have a palette of 256 colours from 32,768 - because in that mode the byte you store doesn't mean anything in itself, and as long as I have 15 pins left from the 24 available to the LCD controller I can wire them up and neither users nor programmers will know anything is amiss.  (Unless they look directly at the hardware LUT encoding.)

But direct colour mode - where you write 16-bit pixels and they get fed out to the matching pins by the LCD controller - is a non-starter, because a good number of those matching pins simply aren't there if you also want Ethernet.  Which is a pain because I had some ideas for using that behind the scenes to expand on what the hardware can deliver directly.

An option would be to move Ethernet off to a separate chip, but QSPI also interferes with some of the LCD pins, and the whole point of that is that it allows you to memory-map NOR flash and run code straight out of cheap external ROMs.

There is a fix that solves everything, but it introduces its own problems.  There's a 265 pin BGA package of this chip that has all the LCD controller signals on their own dedicated pins.  No conflicts with anything at all.  And physically it's the same size as the 100-pin version.

But (a) BGA packages are a huge pain to prototype with, (b) it costs 50% more, and (c) it would likely require a 6-layer board just to route out all those signals.  It would be cheaper to add two more of the 100-pin version than to do that.

Well, I'll keep plugging away.

Disclaimer: LCD_B2 or RMII_TX0, that is the question.

Posted by: Pixy Misa at 12:22 AM | Comments (2) | Add Comment | Trackbacks (Suck)
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1 "Arm and Global Foundries are partnering on a new 3D chip design."

So they're playing Spock to everyone else's Khan.

"Enjoy your $1000-plus smartphones, folks."

Heh.  I just got a GS9 a couple weeks ago for $449.  Oh no--it's "only" an SD 845!

Posted by: Rick C at Sunday, August 11 2019 10:16 AM (Iwkd4)

2 Yeah.  While the ubiquitous A53 cores are getting a bit long in the tooth, something one or two or even three generations removed from the current high end works fine for almost everything.

Posted by: Pixy Misa at Sunday, August 11 2019 12:57 PM (PiXy!)

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Apple pies are delicious. But never mind apple pies. What colour is a green orange?

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