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usb: device_next: allow to initialize multiple CDC ACM instances #104697

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usb: device_next: allow to initialize multiple CDC ACM instances #104697

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7 changes: 7 additions & 0 deletions doc/connectivity/usb/device_next/cdc_acm.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,13 @@ As the configuration would be identical for any board, there are common
:zephyr_file:`Kconfig file <boards/common/usb/Kconfig.cdc_acm_serial.defconfig>`
that must be included in the board's devicetree and Kconfig.defconfig files.

The number of initialized CDC ACM instances is one by default.
If the application requires multiple CDC ACM serial backends, the number of
registered and initialized instances can be increased using
:kconfig:option:`CONFIG_CDC_ACM_SERIAL_INSTANCES_NUMBER`.
The order of the instances is not guaranteed. For identification purposes, a
host application needs to use the label property of the CDC ACM UART node.
Comment on lines +100 to +105
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@tmon-nordic tmon-nordic Mar 2, 2026

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Can you link to the source behind "Several users have requested the ability to register and initialize multiple CDC ACM instances"? The solution here is very questionable.

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@Damian-Nordic Damian-Nordic Mar 3, 2026

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@tmon-nordic I can provide more details :).

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@tmon-nordic tmon-nordic Mar 3, 2026

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Is there anything specific to require having a dedicated Kconfig option? Why not just iterate over all zephyr,cdc-acm-uart compatibles?


Using CDC ACM UART in the application
=====================================

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10 changes: 10 additions & 0 deletions subsys/usb/device_next/app/Kconfig.cdc_acm_serial
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Expand Up @@ -23,6 +23,16 @@ config CDC_ACM_SERIAL_ENABLE_AT_BOOT
When disabled, the application is responsible for enabling/disabling
the USB device.

config CDC_ACM_SERIAL_INSTANCES_NUMBER
int "Maximum number of initiliazed CDC ACM instances"
range 1 7
default 1
help
Register and initialize up to a selected number of CDC ACM instances.
These instances will not be available for other configurations or USB
device contexts. This number must not be higher than the number of
available instances.

config CDC_ACM_SERIAL_MANUFACTURER_STRING
string "USB device manufacturer string descriptor"
default "Zephyr Project"
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23 changes: 15 additions & 8 deletions subsys/usb/device_next/app/cdc_acm_serial.c
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Expand Up @@ -43,11 +43,15 @@ USBD_CONFIGURATION_DEFINE(cdc_acm_serial_hs_config,
attributes,
CONFIG_CDC_ACM_SERIAL_MAX_POWER, &hs_cfg_desc);

BUILD_ASSERT(CONFIG_CDC_ACM_SERIAL_INSTANCES_NUMBER <= DT_NUM_INST_STATUS_OKAY(zephyr_cdc_acm_uart),
"CONFIG_CDC_ACM_SERIAL_INSTANCES_NUMBER is higher than number of CDC ACM instances");

static int register_cdc_acm_0(struct usbd_context *const uds_ctx,
const enum usbd_speed speed)
static int register_cdc_acm(struct usbd_context *const uds_ctx,
const enum usbd_speed speed)
{
struct usbd_config_node *cfg_nd;
char name[] = "cdc_acm_0";
const int idx = 8; /* -^ */
int err;

if (speed == USBD_SPEED_HS) {
Expand All @@ -62,10 +66,13 @@ static int register_cdc_acm_0(struct usbd_context *const uds_ctx,
return err;
}

err = usbd_register_class(&cdc_acm_serial, "cdc_acm_0", speed, 1);
if (err) {
LOG_ERR("Failed to register classes");
return err;
for (int n = 0; n < CONFIG_CDC_ACM_SERIAL_INSTANCES_NUMBER; n++) {
name[idx] = '0' + n;
err = usbd_register_class(&cdc_acm_serial, name, speed, 1);
if (err) {
LOG_ERR("Failed to register %s", name);
return err;
}
}

return usbd_device_set_code_triple(uds_ctx, speed,
Expand Down Expand Up @@ -105,13 +112,13 @@ static int cdc_acm_serial_init_device(void)

if (USBD_SUPPORTS_HIGH_SPEED &&
usbd_caps_speed(&cdc_acm_serial) == USBD_SPEED_HS) {
err = register_cdc_acm_0(&cdc_acm_serial, USBD_SPEED_HS);
err = register_cdc_acm(&cdc_acm_serial, USBD_SPEED_HS);
if (err) {
return err;
}
}

err = register_cdc_acm_0(&cdc_acm_serial, USBD_SPEED_FS);
err = register_cdc_acm(&cdc_acm_serial, USBD_SPEED_FS);
if (err) {
return err;
}
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