Post AxjadDasFuRjAqYm2K by matt@toot.cafe
 (DIR) More posts by matt@toot.cafe
 (DIR) Post #Axjacl0kWcueWhRWqG by matt@toot.cafe
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       Is there any ARM64 SoC that can boot to Linux without either requiring a DRAM controller initialization/training blob or punting the whole boot process to a second processor running wholly closed firmware? That second one rules out Raspberry Pi (for personal projects). I'd grudgingly accept ARM Trusted Firmware persistently running in the background if the SoC's branch/fork of that is fully open-source. But I still don't like how much code has to run before you get to the OS kernel.
       
 (DIR) Post #AxjacmLhYDGafyFm8e by mntmn@mastodon.social
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       @matt ones i know of: LS1028A (maybe some other LS too, those who have qoriq ddr controller), i.MX6 family, ZYNQ-7000 family
       
 (DIR) Post #AxjacneAj1dShXu2ZE by matt@toot.cafe
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       I found what seems to be the ideal 32-bit Linux-capable ARM platform in terms of boot transparency and simplicity: the Microchip (formerly Atmel) SAMA5 platform, based on a Cortex-A5 core (I think it's always a single core) and LPDDR2 DRAM (up to 512 MB in the boards I've seen). The official boot loader, at91bootstrap3, is MIT-licensed, including DRAM initialization code. It can chain to u-boot, load a Linux kernel directly, or load an arbitrary bare-metal program.
       
 (DIR) Post #Axjad5mzGzNky6AKo4 by matt@toot.cafe
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       But, I can't find a currently sold evaluation board with an audio DAC and headphone jack on-board.
       
 (DIR) Post #Axjad7X6mzrwNQkgKm by matt@toot.cafe
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       The SAMA5 platform really does have the least bad boot process I've found in any recent-ish (though only 32-bit) Linux-capable ARM SoC. According to the SAMA5D2 series datasheet (https://ww1.microchip.com/downloads/aemDocuments/documents/MPU32/ProductDocuments/DataSheets/SAMA5D2-Series-Datasheet-ds60001476.pdf), it has a 64 KB boot ROM. In standard (non-secure) mode, that ROM reads the second-stage boot loader from a boot.bin file on an SD/MMC device's FAT partition. That's practically perfect IMO. And the boot.bin in the buildroot config I tried is 14 KB. That loads u-boot which is ~400 KB.
       
 (DIR) Post #Axjad9fgq3vD0cmYzI by matt@toot.cafe
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       Oops, meant 64 KB boot ROM! Edited the toot.
       
 (DIR) Post #Axjad9iAgpuH8JwXr6 by matt@toot.cafe
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       And like I said, that second-stage boot loader (boot.bin) can apparently be configured to skip u-boot and go straight to Linux or some other bare-metal program.The datasheet does mention a secure boot mode, for which documentation is only available under NDA. Not ideal, but I don't want secure boot anyway.
       
 (DIR) Post #AxjadBln2LzPW7eSm0 by matt@toot.cafe
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       BTW, I ended up not ordering a Raspberry Pi Pico-based microcontroller board like I was thinking about doing last weekend. A SAMA5 board, if I can get one with an audio DAC and headphone jack built-in or as an add-on, would split the difference between a microcontroller and an application processor, as the SAMA5 platform explicitly advertises bare-metal support with sample code.
       
 (DIR) Post #AxjadDasFuRjAqYm2K by matt@toot.cafe
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       I wish the creators of the Raspberry Pi had been working at Atmel rather than Broadcom. A wildly popular hobbyist SBC with built-in audio DAC and headphone jack based on the SAMA5 SoC family would have been perfect!Frustratingly, there _was_ a SAMA5 evaluation kit with built-in audio DAC and headphone jack, but it's now discontinued. Presumably not enough demand for that particular combination.
       
 (DIR) Post #AxjadFBQLVHE6UfTe4 by matt@toot.cafe
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       The bare-metal SDK for the SAMA5 family and some other SoC's (https://github.com/atmelcorp/atmel-software-package) even include audio examples, with configurations for the discontinued eval kit.
       
 (DIR) Post #AxjadGn2N8xT5RH1ua by matt@toot.cafe
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       I'm talking about this eval kit: https://www.microchip.com/en-us/development-tool/ATSAMA5D4-EK It basically had everything except WiFi, including audio codec, USB, Ethernet, and even HDMI. And apparently the SAMA5D4 SoC does have video decode (probably a proprietary driver for that). DigiKey knows about that eval kit, but lists it as obsolete, and provides a coipy of this document explaining why: https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/918/WE152301.pdf But the newer, lower-cost SAMA5D4-Xplained board doesn't have audio!