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Raspberry Pi Zero 3 W and Pi 4 Model A appear in kernel device trees

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Raspberry Pi Zero 3 W and Pi 4 Model A appear in kernel device trees

Two new Raspberry Pi boards have quietly turned up in Raspberry Pi's Linux kernel tree: a Raspberry Pi Zero 3 W and a Raspberry Pi 4 Model A. Phoronix spotted the device tree files first. There is no official announcement yet, so everything below is the blogger bret.dk's reading of the files, not a spec sheet.

The Zero 3 W is the bigger surprise. Its device tree names the Broadcom BCM2711 as the SoC, the same quad-core Cortex-A72 chip that powers the Raspberry Pi 4. It would replace the quad-core 1GHz Cortex-A53 RP3A0 in the Zero 2 W, which launched almost exactly five years before the post. That is a big step up in per-core performance, but the author wonders how hot it will run, since the BCM2711 is not known for running cool and a Zero has little board to spread heat into. The device tree gives no clock speeds, so it is unknown whether they have been dialled back from Pi 4 levels.

Other details the author draws from the Zero 3 W file: the storage controller is set up with an 8-bit bus width and a comment calling it the eMMC/SD card, which suggests eMMC, but the author does not expect that on the final board because it would raise the price. He suspects it is a leftover or an option kept open during development, with microSD the likely outcome. GPIO names include SPI flash lines, which suggests the same EEPROM-based bootloader as the Pi 4 (the Zero 2 W never had one). There is a single HDMI output, with the second HDMI controller permanently disabled. A power button is defined on GPIO 46 and mapped to KEY_POWER, so a physical button, or at least a header for one, may come, much like the Pi 5. Wi-Fi and Bluetooth are wired as on the rest of the BCM2711 family, there is one ACT LED, and the GPIO layout is the usual 40-pin one (GPIO 0-27 with the ID EEPROM pins), so existing HATs should be fine.

Two items are more speculative. The PCIe controller is enabled, with lines named PCIE_PWR_EN and PCIE_DET_WAKE, and the camera side has a 4-lane CSI configuration rather than the 2-lane one on the Pi 4 Model B. Both device trees share a lot of copy-and-paste (the Zero 3 W even has a duplicated PWR_GPIO line name), so the author would not read much into either until a real board appears.

The Pi 4 Model A is the first Model A since the Raspberry Pi 3 Model A+ in 2018. The Model A recipe is to take the Model B, strip out what most people can live without, and cut the price; the author says the 4 Model A follows it closely, though the price part may not hold. The file shows no Ethernet: the controller is not enabled and the GPIO lines that drive the Ethernet PHY on the Model B have been repurposed. It has a single HDMI output instead of the Model B's dual micro HDMI. There is no 3.5mm audio/composite jack, since the analogue audio pins are empty and the composite video encoder is disabled, so audio would go over HDMI (or USB or I2S). Storage is microSD only, with the same 1.8V signalling support as the Model B for faster UHS modes. The author finds the antenna support most interesting: two antenna control lines (ANT_CTRL1 and ANT_CTRL2) and overlay parameters named ant1, ant2 and noant, which is how the Compute Module 4 switches between its onboard antenna and an external U.FL connector. It also has PWR and ACT LEDs, the same SPI flash bootloader setup as the Model B, and the same power button definition as the Zero 3 W.

The device tree says nothing about USB. USB 3 on the Model B used the PCIe bus and PCIe is enabled here, so USB 3 is possible, but the 3 Model A+ had a single USB-A port and the author would expect the same.

What is unknown: device trees do not describe RAM, and there is nothing on pricing, clock speeds, connector types or a release date. The author thinks a lower-cost Pi 4 variant makes sense given recent memory price rises, while calling the Zero 3 W harder to judge, because the Zero range lives and dies by its price and he cannot imagine the BCM2711 being as cheap to build around as the RP3A0. His verdict is positive, with the caveat that mileage may vary when the real boards arrive. He adds that kernel support landing ahead of launch is usually a good sign a launch is not far off.

Key facts

  • Device tree files for a Raspberry Pi Zero 3 W and a Raspberry Pi 4 Model A have appeared in Raspberry Pi's Linux kernel tree; Phoronix spotted them first and there is no official announcement.
  • The Zero 3 W device tree names the BCM2711 (quad-core Cortex-A72, as in the Pi 4) instead of the Zero 2 W's quad-core 1GHz Cortex-A53 RP3A0; clock speeds are not given.
  • The Zero 3 W file shows a single HDMI output, a power button on GPIO 46 mapped to KEY_POWER, SPI flash bootloader lines and the usual 40-pin GPIO layout.
  • The Pi 4 Model A, the first Model A since the 3 Model A+ in 2018, shows no Ethernet, one HDMI output, no 3.5mm jack, microSD only, and two antenna control lines for an external antenna.
  • Pricing, RAM, clock speeds, USB details and release date are unknown; the PCIe and 4-lane CSI entries may be copy-paste leftovers, according to the author.

Why it matters

The Zero 2 W launched almost exactly five years before the post, so a successor has been a long time coming. If the Zero 3 W ships with the BCM2711, it would move the Zero line from a quad-core 1GHz Cortex-A53 to the quad-core Cortex-A72 used in the Pi 4, which the author calls a big step up in per-core performance. The 4 Model A would be the first Model A since the 3 Model A+ in 2018 and would stretch the Pi 4 platform with a cheaper, cut-down board. Kernel support appearing before launch is, in the author's words, usually a good sign a launch is not far off.

Who it affects

Anyone who has wanted a faster Zero since the Zero 2 W, and people who want a cheaper, smaller Pi 4 and do not need Ethernet or dual HDMI. The author singles out external antenna support on the 4 Model A as useful for people mounting a Pi in a metal enclosure. Owners of existing HATs are touched too: the Zero 3 W file shows the usual 40-pin GPIO layout, so the author says existing HATs should be fine.

How to use it

Nothing can be bought or used yet, because neither board has been announced and no release date is known. For now the files are a preview: the Zero 3 W points to a Pi 4 class chip with the Pi 4's EEPROM bootloader and a 40-pin header, and the 4 Model A to a stripped Model B with microSD, one HDMI port and audio over HDMI (or USB or I2S). The author plans to add both boards to his sbc.compare site once he can get one in hand.

How solid is it

The files themselves are real: they sit in Raspberry Pi's Linux kernel tree, and Phoronix reported them first. The hardware details are the blogger's interpretation, not a spec sheet, and the source names are the device tree file names (bcm2711-rpi-zero-3-w.dts and bcm2711-rpi-4-a.dts), so final product names are not confirmed. The eMMC, PCIe, 4-lane CSI and physical power button points are inference or speculation by the author. Raspberry Pi has made no announcement.

Risks and caveats

The author warns that both device trees share a lot of copy-and-paste, including a duplicated PWR_GPIO line name in the Zero 3 W file, so the PCIe lines and 4-lane CSI may not reflect real hardware. Open questions include heat and clock speeds on the Zero 3 W, price for both boards (the author doubts the BCM2711 can be as cheap to build around as the RP3A0), RAM, connector types and USB. He says mileage may vary when the real boards turn up.

“device tree files tend to give away a surprising amount if you can decipher them and I gave it my best shot”

— bret.dk, blog post