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I tend to disagree
what-ever system is pre-loaded, you will find people that complain or want something else.

I like the idea of having only the blink preloaded to prove functionality of a new...

I only wanted to clarify the "d - first dump list of storages" option
this prints out the relevant info of the index file, mtp uses to access the files.
It is only useful during development and...

One application of MTP is to transfer files, while the Teensy is not accessible, so disk access should IMO be optimised.
If this can be done using info from filesystem, so better. Yes, FS.h should...

Well, I only adapted the original code to my needs and made it available.
I understand that Paul is interested to integrate it at some time, but he seems to be busy with other (hopefully pleasant)...

The 2.9 ms is result of acquisition buffer (128 samples) and sampling rate (44.1 kHz) so you must change one of the two values to change the delay.
This requires changing some basic parameters. It...

They cannot be 180 deg out of phase. there is a fixed travel time through the audio library
Output is NEVER without delay to input.

AFAIK
I2S-input: data are buffered for 128 samples (2.9 ms...

the way it is wired now, connect audio signal to both line in and oscilloscope channel 1 to ,say, left and channel 2 to right
you could simplify, by connecting both amp inputs to same i2s input...

sorry about formating
here is the audio code

#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <SerialFlash.h>

// GUItool: begin automatically generated code

no, I was suggesting
i2s ->mixer (+1) -> I2S left
|-> mixer (-1) -> I2S right
so left and right path have same internal delays

if you insert an audio object then you have to consider a 128 sample delay.
So, insert two mixers in parallel one with +1 and the other with -1, then you should get the desired effect

the SPI speed and the CPU speed are total different clocks
.
However, if you use code where SPI clock speed is derived from CPU clock then you may run into issues.
If this happens in old low...

use
SPI1.beginTransaction(SPISettings(4'000'000, MSBFIRST, SPI_MODE0));

spi commands

SPI1.endTransaction();

or similar to control SPI speed (here 4 MHz)

which library you are using?
could not find a MPU9250 for SPI that is compatible with your code

I use 5 lines into my waterproof housing
Voltage, Ground, USB D+, USB D-, Program line
this allows me to reprogram Teensy at all circumstances.

Yes but SE
A10,A11 are Differential (it is clearly written)

I corrected the Readme file (thanks for pointing out)

re TyCommander, I'm not using this, so I cannot comment
If you update boards.txt (modifications for teensy_avr) then there should be two...

USB mode is fixed at compile time.
You can use MTP with Serial if you install MTP from https://github.com/WMXZ-EU/MTP_t4 and follow instructions

I had that too, but having storageID above 16 bit did not change anything.
I know it violates the document, but coding was simpler.

one events:
notifying every new file, for me is not an option,...

maybe one needs an ISR also for events. don't think TX ISR is called.

@KurtE
On T3.x, my interpretation was that after malloc you need also a free, but I may be wrong.
So I use always the same buffer for multiple events, assuming that I will not send multiple events...

BTW,
My Github has also a tested T3.6 version on events included (in MTP.cpp)
I would keep event handling outside cores
I did a couple of days ago a PR on teensy3/usb_desc.h to have tx events,...

MTP per se does not need Serial connection, but MTP is usually integrated in other programs that need serial connections.

Seremu without Arduino monitor is a little bit complicated.
Consider...

@KurtE,
Yes I'm following your modifications and try them out.
There are couple of things I may have a different starting point, so I'm curious to see how they work out.
So please go ahead with...

That is my observation also.
F5 seems to be necessary

and 3 characters after the "."

Teensy4.x are 3.3V I/O so do do not want a board that is made to interface with a 5V board.
5V in Teensy4 pins may kill these pins

what about

extmem_malloc(size)
as used in LittleFS_RAM of LittleFS library?

Chip,
mtp-test.ino does work now with T3.6
to use USB_MTPDISK_SERIAL you need to copy the desc.h parts into desc.h cores files
if you prefer to use old mtpdisk (seremu) you should edit desc.h to...

Chip,
Have not integrated yet events to T3.6.
I'm still testing with T4.1 (my real application runs on T4.1)
T3.6 needs own usb interface so it needs a mind-change to get integrated.
otherwise it...

Chip
you mean
N_k = (Q * f_s) /f_k

anyhow, it does not matter, as one can use FFT to approximate the spectral resolution (with summing of bins), then one can sum the temporal bins to...

AFAIK
N_k * f_k = Q*f_s

N_k window length
f_k center frequency
f_s sampling frequency

see e.g. https://en.wikipedia.org/wiki/Constant-Q_transform
Obviously, one needs to read a little bit...

Chip,
I would not call it "approximation to constant-Q", as a simple logarithmic frequency scale (logarithmic summing frequency bins) is equivalent to a logarithmic Q.
In how far logarithmic...

The OP and title asks about constant Q and not "logarithmic" spectrograms.
constant Q indicates "logarithmic" spacing of frequencies AND therefore also logarithmic changes in window size.
summing...

As Q is related to the time-frequency product you "only" need to implement 96 DFTs, each with own window size.
Edit: Not sure is there is a DFT object in Audio library, but you can easily write one...

@KurtE
Re storageID, I knew this and have thought to separate physical and logical storage, but in the end I let everything as 1 physical storage (0<<16) and consider all storage as logical. I know...

After commenting to @mborgerson, here a first success
I succeeded to provoke a PC response using an event.
Using a device reset event PC reopened a new session. I updated the MTP github.
in MTP.h...

Correct, If PC initiated a session, and you open a directory in file explorer MTP responder tells MTP initiator (PC), how many files are in this directory. If Teensy the writes additional files, PC...

I do not understand.
Does the ReadWrite.ino example in SD library not work?
Is it not the purpose of SD library that you do NOT interface directly with the SdFat library?
The OP asked for a simple...

Let me summarize the discussion as I see it.

Starting point:
MTP was developed to retrieve files from portable devices and at the same time to store files on such devices.
It was never designed...

You may start with
https://forum.pjrc.com/threads/65235-Basic-I2S-Input-Example-for-T4-x

This is an operation from within the Teensy. IMO, what is needed an operation on PC to reset session.
I have good results with using the device manager, but as I said, I hear that others have...

If you are not deploying it in coastal areas that gets flooded within the next century.

@KurtE,
A lot of suggestions.
Not sure if it is useful to map FS with MTP (or I misundertand).
The main program must know the disks attached to system for logging, and the MTP is not talking to...

Personally, I have no experience with Ethernet, but I can imagine that others on this forum would appreciate a picture of your setup. Not sure also if ethernet kits from e-bay are suited for T4.1....

The following snippet does not crash

uint32_t data;
int ndat = file.read(&data,4);
if(ndat<0) Serial.println("SD error");


OK, a return of -1 indicated SD read failure, which may be...

I'm pretty sure that nobody on this forum is experimenting with intentionally bricking a teensy.
So you will not get an affirmative answer, but we all are waiting that you tell us that this...

The following code is a simple I2S input example that runs on T4.1.
It can be configured to have multi channel TDM input for ether 16 or 32 bit for (nearly) arbitrary sampling frequency.
It runs...

on this forum, threads are not deleted. And maybe you give also the solution to the OP to help others

Better not to interfere with DMA that is running in parallel,

Obviously, you will get better answers from Microsoft, why their plugin does not work on a Mac, or better ask Apple, why VSCode + Arduino plugins do not work on MAC.

To answer directly, I have not...