nrf5340 is unable to trigger rpmsg(ipc) transfer

[Dumam]

Hi,

I have quite demanding SPI device which should send its data over BLE.
Thanks to throughput example i was able to achieve maximum transfer speeds for synthetic tests (without SPI).
Sadly after adding real data input, I noticed that no transfer is executed until I finish my commands. 

Thanks to SystemView I was able to narrow this problem to one part of configuration -> rpmsg.

Colors:

Green -> spi thread
Yellow -> bt_hci thread
Orange -> ble host TX
Red (small squere in top) - IRQ 58 from probably ipc, but i wasnt able to find it in manual (not listed)
Blue - probably openAmp mailing work queue thread
purple - systemwork queue

SystemView Data Log
4010.BleProblem.dat

Here is repo with configs etc.
https://github.com/DuMaM/bitly_nrf5x

[Edvin]

Hello,

I am not sure I understand the question? What are you seeing, and how do you expect it to work?

I noticed that no transfer is executed until I finish my commands. 

What sort of commands are you talking about here?

BR,
Edvin

[Dumam]

 Edvin Thanks for response, and sorry to not be clear enough. 

This is what i'm doing here:
-> I have ads129x communication over SPI. It's set to work in continuous mode, so every n seconds it sends data packet (24bytes). To notify that we should get them it pulls up DATA_READY pin. I detect this in ISR callback and via semaphore i'm notifying SPI thread to read data. (GREEN part in picture)
-> after SPI read this it send that data via pipe to other thread which is packing up data for BLE transfer, every time i get 251 bytes in this thread I'm sending this with `bt_gatt_write_without_response`. (YELLOW part in picture)

The question is:
why it takes so long rpmsg to start transmit data and why there are so big delays between each frame. (BLUE part in picture)

[Edvin]

I believe it is rather the work queue holding you back than the BLE stack. You can try to either skip the work queue, and call the bt_gatt_notify_cb() directly from your spi callback handler.

[Dumam]

Ok, I added BLE call inside SPI callback.
https://github.com/DuMaM/bitly_nrf5x/pull/13
I got even worse performance ;( 

BTW. I'm using bt_gett_write_without_response, which is under the hood:

static inline int bt_gatt_write_without_response(struct bt_conn *conn,
						 uint16_t handle, const void *data,
						 uint16_t length, bool sign)
{
	return bt_gatt_write_without_response_cb(conn, handle, data, length,
						 sign, NULL, NULL);
}

[Dumam]

[Dumam]

Dear Edvin 
bt_write_without_response is locking function, which is bad for me because my SPI do not have time to prepare new data for connection event. 
I'm looking for something what will help me in determining if i have still space in in my TX buffers.
According to docs.zephyrproject.org/.../l2cap.html , there is nothing like that.

[Edvin]

Can you please check my colleague, Einar's replies in this ticket:
bt_gatt_notify() can block when running on Zephyr workqueue.

In general, you should not call bt_gatt_notify_cb() from a workqueue, because it can lead to a deadlock, or in some cases, blocking calls, as you see here. Try calling it from another context. 

Best regards,

Edvin

[Dumam]

Thanks for this reply, but:

1. I posted URL to my code where you can easily track that I'm not using work queue but separate thread.
I posted a print screen from Seeger System View, where there is only info about thread
2. I call there bt_gatt_write_without_response_cb(), which calls bt_gatt_write_without_response_cb(). This calls still blocks thread execution. 
3. My issues are the same as ones mentioned here, for the same board, for the same situation:
What's different in my case is that I'm using a `write without response` not notify.
Fast notifications with nRF5340 and nRF Connect SDK

4. For this board, if you use BLE stack anywhere, then net CPU is included.
This converts the project to multicore one and adds a simple rpmsg project for net-core and installs SoftDevice by default on it.
After that in config you can also see that HCI RPMSG stack is enabled for app core. 
So every command from app-core to HCI BLE is sent via RPMSG module.
This module uses RPROC protocol and MBOX module to sync over IPC.
Sadly, to process this in correct manner, MBOX module is using WORKQUEUE.

I guess this is the main reason for locks.
If this issue is true.
bt_gatt_notify() can block when running on Zephyr workqueue.

5. nrf52840 has different driver HCI RPC, but there is similar WORKQUEUE implemented to sync with SoftDevice.

[Dumam]

Hi,
The issue persists. I was able to partially overcome it, by changing net core BLE Stack implementation in hci_rpmsg_nrf5340dk_nrf5340_cpuapp.conf to:

# select ll layer
CONFIG_BT_LL_SW_SPLIT=y
CONFIG_BT_LL_SOFTDEVICE=n
#CONFIG_BT_CTLR_SDC_MAX_CONN_EVENT_LEN_DEFAULT=4000000

 

After this change, I was able to achieve 1,1Mbps of throughput. 
I still will be fighting with this code to reach 1,4Mbps, but It can be hard to do so.

According to System View, not much room left for processing.

If I find something useful, I will post it here.

[Dumam]

Both nrf52840 and nrf5340 have bigger throughput with Zephyr stack.
If I replace this with SoftDevice stack, then throughput drops to 500kbps.

Edvin If you're interested I can prepare an example project which will reproduce my case only with two nrf5340 boards, without any SPI device (it can be in loopback).

[Edvin]

Hello,

Sorry for the late reply. I was unexpectedly out of office since Thursday.

That would be great. If I can have a look, reproduce it and run it by our SoftDevice controller, I can ask them whether they have any hints on whether it is the intended workflow, or if this is in fact a bug.

Best regards,

Edvin