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by jdb
Sat Feb 20, 2021 5:52 pm
Forum: General
Topic: Setting PWM Frequency - odd results
Replies: 4
Views: 419

Re: Setting PWM Frequency - odd results

Hmm. 992.086 = (125/126) * 1000.023 - almost like there's an off-by-one in the division from the system clock, and for other frequencies it smells like bad rounding.

Can you dump the contents of the CHx_DIV registers in the PWM block for each of your settings?
by jdb
Tue Feb 16, 2021 9:30 am
Forum: Advanced users
Topic: What is the serial number for Pi4?
Replies: 2
Views: 392

Re: What is the serial number for Pi4?

i'm also curious as to why there is a stray bit in that value It's to differentiate a non-Pi 4 serial from a Pi 4 serial. Entering a Pi 4 serial into the web store to buy codec keys (even though there's a big banner saying it won't work) causes the web store to reject the transaction because it exp...
by jdb
Fri Feb 12, 2021 8:47 pm
Forum: Advanced users
Topic: Analogue audio redux
Replies: 125
Views: 52168

Re: Analogue audio redux

The blog post you linked to is orthogonal to the behaviour of the firmware on Pi 2. There may be a regression in clock behaviour (or rather, previous implied behaviour that's no longer consistent) which is worth investigating. In your sample wav file, I can't detect any discontinuities - either thro...
by jdb
Fri Feb 12, 2021 2:25 pm
Forum: SDK
Topic: Why so big?
Replies: 39
Views: 2188

Re: Why so big?

I suggest running readelf -S blink.elf. It may be illuminating.
by jdb
Tue Feb 09, 2021 2:39 pm
Forum: General
Topic: Pico as Pi peripheral
Replies: 31
Views: 3863

Re: Pico as Pi peripheral

Perhaps your implementation is deserving of its own thread?

(To promote it further, not because it's off-topic in this one.)
by jdb
Tue Feb 09, 2021 2:21 pm
Forum: General
Topic: GPIO protection diode (shunting over-voltage)
Replies: 11
Views: 1073

Re: GPIO protection diode (shunting over-voltage)

This is where the other bonus feature of the non-ADC pins comes into play. If Pico VDDIO is unpowered, then the pins can tolerate up to 3.63V (absolute max) applied. This does not apply to the ADC pins - the ESD diode will be forward-biased if an analogue voltage is still applied when Vref or VDDIO ...
by jdb
Tue Feb 09, 2021 8:10 am
Forum: Advanced users
Topic: Analogue audio redux
Replies: 125
Views: 52168

Re: Analogue audio redux

Time ARM Core H264 Core Temp (Max) IRQ/s RX B/s TX B/s GPUMem Free MemFreeKB / %used Accum GPU B Mem kB ======== ======= ======= ======= =============== ====== =========== =========== =========== ================= ======================= 00:28:32 600Mhz 250Mhz 350Mhz 51.92C (53.00C) 10,777 0 0 152M...
by jdb
Mon Feb 08, 2021 4:39 pm
Forum: General
Topic: GPIO protection diode (shunting over-voltage)
Replies: 11
Views: 1073

Re: GPIO protection diode (shunting over-voltage)

The schematic in the Pico datasheet states; "ADC GPIO pins have diode to VDDIO (other GPIO do not)". wherever diodes in IO pins are referenced, it should parse as "ESD protection diodes" If we do that - "ADC GPIO pins have ESD protection diodes to VDDIO ( other GPIO do not ...
by jdb
Mon Feb 08, 2021 3:16 pm
Forum: Advanced users
Topic: Analogue audio redux
Replies: 125
Views: 52168

Re: Analogue audio redux

Are you setting gpu_freq high with recent firmware? Use of audio does not specifically trigger turbo mode, so what happens if you set gpu_freq=400 or greater / force_turbo=1 (and remove disable_auto_turbo) in config.txt?
by jdb
Mon Feb 08, 2021 2:08 pm
Forum: Compute Module
Topic: Interrupt load on xhci using USB3.0
Replies: 34
Views: 2467

Re: Interrupt load on xhci using USB3.0

Even assuming that the PC BIOS loader is doing something "special" that results in a card that works without interrupt storms, extracting firmwares bundled with BIOSes is probably not a viable course of action - there are no guarantees that the FW loader is guaranteed for chips you find in...
by jdb
Mon Feb 08, 2021 1:12 pm
Forum: General
Topic: GPIO protection diode (shunting over-voltage)
Replies: 11
Views: 1073

Re: GPIO protection diode (shunting over-voltage)

In the ARM world it appears that "ESD protection diodes" are not the same as "clamping diodes" as may be found in other microcontroller devices. I suspect it's the same here. The schematic in the Pico datasheet states; "ADC GPIO pins have diode to VDDIO (other GPIO do not)&...
by jdb
Mon Feb 08, 2021 10:26 am
Forum: SDK
Topic: Random number generator - an example
Replies: 14
Views: 1745

Re: Random number generator - an example

With whitening it's still by no means perfect (or even decent enough to seed rand() with). For a "known unreliable" pseudo RNG like this one, using a stirring function with an entropy credit is the way to go. You can set the entropy credit to an arbitrarily pessimistic number to avoid pred...
by jdb
Sun Feb 07, 2021 9:46 am
Forum: SDK
Topic: Random number generator - an example
Replies: 14
Views: 1745

Re: Random number generator - an example

The "randomness" has a thermal source - the noise on the input to each of the buffers (connected in a ring - hence ring oscillator). Bias comes from a number of sources but most will be introduced by the ring osc being close to a rational fraction of the sampling frequency. At a minimum I'...
by jdb
Fri Feb 05, 2021 7:42 pm
Forum: General discussion
Topic: 2G RPI 4B base model not available UK
Replies: 28
Views: 3081

Re: 2G RPI 4B base model not available UK

While one always hopes for the best, there have been chip shortages affecting many major companies. Companies with deep enough pockets to pay to "jump the queue" on wafer starts. I haven't seen anything to suggest that this is affecting the production of Pis (and is less likely to than co...
by jdb
Fri Feb 05, 2021 12:10 pm
Forum: Compute Module
Topic: Interrupt load on xhci using USB3.0
Replies: 34
Views: 2467

Re: Interrupt load on xhci using USB3.0

The plot thickens. On a Windows pc with a Gigabyte GA-z170x board, the controller isn't detected. Loading drivers specifically from the card manufacturer (not generic Renesas ones) makes it work, but it's on a per-boot basis (EEPROM isn't flashed). I then moved to a Linux PC with an Asus motherboard...
by jdb
Fri Feb 05, 2021 12:24 am
Forum: General discussion
Topic: Another Pi4 layout
Replies: 11
Views: 684

Re: Another Pi4 layout

RPF / RPT do not issue a Publically available Roadmap of future products. I understand that. I just wanted to get the conversation started in the "hopes" that somebody from RPF/RPT might see it and think "why not?". ok yep we'll have a model conforming to your specifications ava...
by jdb
Thu Feb 04, 2021 10:20 pm
Forum: General discussion
Topic: Raspberry forum censorship (locking and locking)
Replies: 1
Views: 532

Re: Raspberry forum censorship (locking and locking)

You seem to be under a misapprehension as to the nature of "free speech". This is a privately-owned forum.
by jdb
Thu Feb 04, 2021 2:22 pm
Forum: Advanced users
Topic: Pi 4B - USB has diode to prevent backfeed?
Replies: 5
Views: 771

Re: Pi 4B - USB has diode to prevent backfeed?

It's not a diode, it's a transient voltage suppressor for the 5V input. The connection between USB (downstream) Vbus and onboard 5V on a Pi 4 is the same as on previous boards - via a 1.2A current-limiting switch IC. If enabled, the switch will allow substantial reverse current before disconnecting....
by jdb
Thu Feb 04, 2021 2:16 pm
Forum: General
Topic: ADC Differential Non-Linearity
Replies: 71
Views: 6276

Re: ADC Differential Non-Linearity

I'm not convinced the peaks at codes (2n+1)*512 for n=0,1,2,3 are real - we'd have spotted that during characterisation...
by jdb
Thu Feb 04, 2021 10:46 am
Forum: General
Topic: ADC Differential Non-Linearity
Replies: 71
Views: 6276

Re: ADC Differential Non-Linearity

What happens if you change your sweep limits to either side of the (val % 256 512 = 0) case?

I.e. toggle the GPIO when the ADC exceeds 400-600 or similar, and read out a few thousand samples.
by jdb
Tue Feb 02, 2021 2:29 pm
Forum: Compute Module
Topic: Interrupt load on xhci using USB3.0
Replies: 34
Views: 2467

Re: Interrupt load on xhci using USB3.0

My current assumption is that the card's behaviour is entirely independent of the system it's plugged into. Now that I have a minimal test to provoke bad behaviour, I shall see if it does the same on a PC.
by jdb
Fri Jan 29, 2021 5:12 pm
Forum: General discussion
Topic: sudo bug? Update plans!
Replies: 8
Views: 967

Re: sudo bug? Update plans!

https://www.debian.org/security/2021/dsa-4839 It's already in apt. There is no version number change of the base program, but the package plus debian patches includes the fix. sudo/stable,now 1.8.27-1+deb10u3 arm64 [installed] Provide limited super user privileges to specific users Running apt updat...
by jdb
Fri Jan 29, 2021 4:04 pm
Forum: General
Topic: Have I missed something...
Replies: 113
Views: 7876

Re: Have I missed something...

For point 1, see the errata in the datasheet. Appendix B - RP2040-E5.

As for point 2 - does the mass-storage device appear (with or without the use of picotool)?
by jdb
Fri Jan 29, 2021 3:41 pm
Forum: Compute Module
Topic: Interrupt load on xhci using USB3.0
Replies: 34
Views: 2467

Re: Interrupt load on xhci using USB3.0

Weirdness abounds. I have a USB3.0 analyzer which, when connected, significantly alters the behaviour of the controller. - If I have USB3.0 rx line terminations active when the controller is first probed, it times out (Linux doesn't see required activity within 0.5 seconds) - If I disable USB3.0 rx ...

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