The FET holds off the switch enable until the system reset is released (as the VLI USBHPE output is somewhat badly behaved at power up) - see attached schematic fragment.
USB peripherals should never back-power VBUS like this - so this is bad peripheral behaviour. VBUS applied to an unpowered Pi will cause the rails to charge up and the PMIC will then not start (as it is designed to only start from a known state - all rails less than ~200mV - so it makes sure the pow...
The structure of flyback AC-DC PSUs (wall-wart type) means they generally don't (can't) sink current. As long as your HAT does not sink current and will stop sourcing current when its output voltage is at the regulated set point (5V) or higher it should not 'fight' with any accidentally plugged in U...
These have been removed as they aren't generally useful - they aren't standard parts that are available in the channel and so you can't get hold of the parts or datasheets.
Also, we often change manufacturers (of connectors, say) so they can change over time.
This could also be a power supply noise issue - the HDMI PHY uses both 3V3 and 1V8, so one thing to check is your supplies are clean and sequenced properly (compare them with CMIO3 board).
When the CM3 does not start can you measure the voltage across C42 on the CM3 (bottom right corner of the module next to L1). I'm finding it hard to explain why it works on a CMIO3 but on a CMIO1 (with VBAT at 5V) it does not - as these boards really are identical except the VBAT power and the CMIO3...
Can you explain why there are 2 3V3 traces (blue and yellow)? Also can you explain why the traces start at ~500mV (the yellow one then drops down before rising again)? Residual voltages on power rails is a not-uncommon cause of these kind of power-up issues. Some idea of your powerchain architecture...
With your LED on EMMC_EN_N you are just measuring the forward LED voltage drop (through 10K to 3V3). Seems to be working to me. This feels like a power supply issue, the CM3 takes a lot more current from VBAT. What is the capability of your upstream power supply? (I.e. the 5V input) You need to look...
Hi Milek7 while we don't guarantee anything outside of 3V3+/- 5% (mostly due to HDMI voltage requirements to meet HDMI certification) I would be surprised if you had any issues running down at 3.0V
Hi themeerd. Are you using the very latest rpiboot software, and what platform are you using to flash with? (PC, Mac, Pi?, which OS?) - are you using a Compute Module IO board and if so which version? What you describe shouldn't be happening, though gsh has fixed a couple of bugs in rpiboot fairly r...
Hi JohW. The supply rails need to be up at all times unless you are powering the entire system down - the reason is there are parasitic diodes in the silicon device(s), as is common to most devices with multiple power domains, that can turn on if say the 3V3 domain goes away but the 1V8 stays up (1V...
Note that the CMIO-V1 supplies the Compute Module's VBAT from the 3V3, whereas on CMIO-V3 it is supplied from 5V. CM3 can pull significantly more current from VBAT, so if you run heavy CPU loads and/or have anything else using 3V3 it could be marginal. We recommend removing R1 and using a wire to co...
The BCM283x I2S driver doesn't natively support mmap which is required for ALSA to do automatic rate/sample conversion. That setup uses the 'mmap_emul' plugin which emulates it (note the emulator is less optimal in terms of performance but mostly fine).
So I assume you are using GPIO18-21 for the PCM interface which looks OK from the GPIO settings. Your circuit diagram looks OK to me. Looks like the driver loaded OK and so the CM should be sending PCM data. Doesn't look like you used aplay to correctly play a wav file - there is an error you need a...
From http://www.devicetree.org: "The Device Tree is a data structure for describing hardware. Rather than hard coding every detail of a device into an operating system, many aspects of the hardware can be described in a data structure that is passed to the operating system at boot time" Raspberry Pi...