setBuffers useage question

[jimtal001]

Hello Earle, Thank you for your great work here.

Can you explain the use of the setBuffers function used for I2S Input? I am currently working with a single microphone (mono). I've searched for an example or documentation which explains how to use this function parameters but have thus far been unsuccessful in finding one. Maybe you could share an example?

setBuffers(size_t buffers, size_t bufferWords, int32_t silenceSample = 0);

Thanks!

[earlephilhower]

That just sets the amount of RAM that's allocated for buffering input streams. The way I2S works is it fills up bufferWords in one buffer then notifies the app that data is available. So, bufferWords sets the latency before your app is notified, so too large is not great for real-time apps, but too-small will cause excessive IRQs and may overflow.

buffers is the total number of RAM buffers to allocate, each of size bufferWords. You need at least 3 or I2S cannot safely function (ping, pong, and app owned) but there's no particular harm in having more.

Rough guesstimate, I'd use something like 32 or 64 for bufferWords and 4 or 5 for buffers`.

[jimtal001]

Thanks for your help!

Is there a way to call a read command to load the I2S buffer without using interrupts?
Like the esp32 sample code below:

`
void loop() {
size_t bytesIn = 0;
esp_err_t result = i2s_read(...); // load I2S data and place in data buffer

if (result == ESP_OK)
{
// Read I2S data buffer
int16_t samples_read = bytesIn / 8;
if (samples_read > 0) {
// ... do something
}
}
}`

[earlephilhower]

Sure, you don't have to use the onReceive callback and can just use something like

while (audio.available()) {
    int16_t l, r;
    audio.read16(&l, &r);
    /* process... */
}

See the example here.

[jimtal001]

Does the bool available() wait for the buffer to fill before becoming true? The example you linked doesn't set the I2S buffer.

…

On Fri, Feb 23, 2024, 12:05 Earle F. Philhower, III < ***@***.***> wrote: Sure, you don't have to use the onReceive callback and can just use something like while (audio.available()) { int16_t l, r; audio.read16(&l, &r); /* process... */ } See the example here <https://github.com/earlephilhower/arduino-pico/blob/master/libraries/I2S/examples/I2SInput/I2SInput.ino> . — Reply to this email directly, view it on GitHub <#2018 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AB5LB7SWNSWC3DMJ57J4COLYVDK6FAVCNFSM6AAAAABDV6IZ7WVHI2DSMVQWIX3LMV43SRDJONRXK43TNFXW4Q3PNVWWK3TUHM4DKNZRGQ4TM> . You are receiving this because you authored the thread.Message ID: ***@***.*** .com>

[earlephilhower]

available() does what available() does in a Stream, lets you know if you can read data w/o blocking. So it'll return false until there's some data transferred from the HW to the app side.

[jimtal001]

Would you please explain the Boolean returned by an I2S read statement like: read16(...).
Does true mean data was returned? Or something else, like time-out, I2S-error, etc.

As per the I2S.h file: "Read samples from I2S port, will block until data available", so this would indicate that the returned Boolean does not mean data available.

[earlephilhower]

They do block, and always return true when data comes back. It can only return false if the I2S wasn't started or is OUTPUT only.