ENOMEM with MQTT Subscription List

[kingston]

I have a working MQTT subscription list, when I add a new topic for subscription my subscribe fails with ENOMEM error -12.

If I remove another topic, I can add new topics successfully so I know its not syntax or an issue with the topic.  I have increased the stack and heap and still see the error.  Is there any way to dig deeper into what is causing the subscribe error?

[Didrik Rokhaug]

Hi,

How do you add the new topics?

Do you increase the list_count correspondingly?

Best regards,

Didrik

[kingston]

All the topics are statically assigned at compile time into a struct mqtt_topic subscribe_topic. 

After the topic struct is created it is passed to the subscription function with

const struct mqtt_subscription_list subscription_list = {
.list = subscribe_topic,
.list_count = ARRAY_SIZE(subscribe_topic),
.message_id = 1234
};

return mqtt_subscribe(&client, &subscription_list);
}

[kingston]

My current memory settings are:

# Memory
CONFIG_MAIN_STACK_SIZE=20480
CONFIG_HEAP_MEM_POOL_SIZE=16384
CONFIG_NRF_MODEM_LIB_SENDMSG_BUF_SIZE=2048
CONFIG_NRF_MODEM_LIB_HEAP_SIZE=4096
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=8192
CONFIG_THREAD_NAME=y
CONFIG_LOG_STRDUP_MAX_STRING=100

[Didrik Rokhaug]

The .list field in the mqtt_subscription_list struct should be an array, not a single struct.

This works for me:

	struct mqtt_topic subscribe_topics[] = {
		{
			.topic = {
				.utf8 = CONFIG_MQTT_SUB_TOPIC,
				.size = strlen(CONFIG_MQTT_SUB_TOPIC)
			},
			.qos = MQTT_QOS_1_AT_LEAST_ONCE
		},
		{
			.topic = {
				.utf8 = "foo",
				.size = strlen("foo")
			},
			.qos = MQTT_QOS_1_AT_LEAST_ONCE
		}
	};

	const struct mqtt_subscription_list subscription_list = {
		.list = subscribe_topics,
		.list_count = ARRAY_SIZE(subscribe_topics),
		.message_id = 1234
	};

[kingston]

Thanks I was defining the list as an array, it was just a paste error into Devzone.  It appears that the error is solved after increasing the message and payload buffer size with CONFIG_MQTT_MESSAGE_BUFFER_SIZE=256
CONFIG_MQTT_PAYLOAD_BUFFER_SIZE=256

Without this addition, any time I had more than 7 topics I received the ENOMEM during subscription.

[Didrik Rokhaug]

Ah, that makes sense.

If the packet isn't large enough for all the topics, that would also explain the error you got.

Anyway, it's good to hear that you found the solution!