Creating a VGA Signal in Hubris

moefh a day ago | parent | next [-]

The internal DAC in most of these microcontrollers is way too slow for VGA. According to this[1], for STM32 you can generally expect at most 1MHz without external additions; that's way too slow even for e.g. 320x240 which has a pixel clock of over 10MHz.

A lot of hobbyist projects use simple improvised DACs made with a few resistors. Here are mine for the ESP32[2] and the RP2040[3] (Raspberry Pi Pico), both use 320x240 (just the standard 640x480 with half the pixel clock and every line repeated to half the resolution in both width and height).

[1] https://www.st.com/resource/en/application_note/an4566-how-t...

[2] https://github.com/moefh/esp32-loser

[3] https://github.com/moefh/pico-loser

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vardump a day ago | parent | prev [-]

RP2040 and RP2350 PIO makes producing VGA signals criminally easy.

But many other µCs can do it too, at least to some degree. Even Atmels.

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lasernoises a day ago | parent | next [-]

I just realized that my keyboard has two of those RP2040's on it, which is giving me some very bad ideas.

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pipo234 a day ago | parent | prev | next [-]

There's probably a well documented backstory on why Oxide choose stm32xx nucleo. I'm guessing VGA signals were not a top priority for hubris

	▲	mkeeter a day ago \| parent \| next [-]
		(I work at Oxide, though I wasn't around for the initial chip selection process) It's at least partially a matter of timing: Oxide was picking its initial hardware in roughly 2020, and the RP2040 wasn't released until 2021. A handful of people have done ports, e.g. https://github.com/oxidecomputer/hubris/pull/2210, but I expect to stick with STM32s for the foreseeable future – we've got a lot to do, and they're working well enough!
	▲	steveklabnik a day ago \| parent \| prev [-]
		The rack has no screens, so no need to drive VGA, it's true. Probably the best history on the choice of going with ARM comes from here: https://news.ycombinator.com/item?id=28989138 The internal RFD on the SP's design still talks about choosing RISC-V, and I don't think (or am simply bad at using search) that the move ended up being in an RFD.

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sitzkrieg a day ago | parent | prev [-]

my thoughts too. this is a hello world bare metal step up. doing it to get to grips w gpio on a full blown os is cool too though