btattach command hanging when using HCI UART sample nrf52840

[samanthacho]

When flashing the chip with a build from the samples/bluetooth/hci_uart via west build -b nrf52840dk/nrf52840 samples/bluetooth/hci_uart --pristine and west flash off the current main of sdk-zephyr, a btattach command from a linux host connected to the Zephyr device over UART hangs indefinitely:

btattach -B /dev/ttyMSM` -S 1000000 -P h4

Attaching Primary controller to /dev/ttyMSM2
Switched line discipline from 0 to 15
= New Index: 00:00:00:00:00:00 (Primary,UART,hci1) #0 [hci1] 4311.006931
= Open Index: 00:00:00:00:00:00 [hci1] 4311.007519
< HCI Command: Reset (0x03|0x0003) plen 0 #1 [hci1] 4311.007671
Device index 1 attached

The bluez version is 5.54, zephyr-sdk is the latest.

Looking at the backtrace on the device via gdb shows the CPU as idle, and no attempts to access the UART are seen.

When attempting to disable the config value CONFIG_BT_CTLR as suggested here, the build fails with the below error. What must be done to enable HCI UART support on the Zephyr device?

-- Zephyr version: 4.0.0-rc2 (/Users/samantha.cho/clones/zephyrproject/zephyr), build: v4.0.0-rc2-53-gb9fc4cc4151f
[139/144] Linking C executable zephyr/zephyr_pre0.elf
FAILED: zephyr/zephyr_pre0.elf zephyr/zephyr_pre0.map /Users/samantha.cho/clones/zephyrproject/build/zephyr/zephyr_pre0.map
: && ccache /Users/samantha.cho/zephyr-sdk-0.17.0/arm-zephyr-eabi/bin/arm-zephyr-eabi-gcc  -gdwarf-4 -gdwarf-4 zephyr/CMakeFiles/zephyr_pre0.dir/misc/empty_file.c.obj -o zephyr/zephyr_pre0.elf  zephyr/CMakeFiles/offsets.dir/./arch/arm/core/offsets/offsets.c.obj  -T  zephyr/linker_zephyr_pre0.cmd  -Wl,-Map=/Users/samantha.cho/clones/zephyrproject/build/zephyr/zephyr_pre0.map  -Wl,--whole-archive  app/libapp.a  zephyr/libzephyr.a  zephyr/arch/common/libarch__common.a  zephyr/arch/arch/arm/core/libarch__arm__core.a  zephyr/arch/arch/arm/core/cortex_m/libarch__arm__core__cortex_m.a  zephyr/arch/arch/arm/core/mpu/libarch__arm__core__mpu.a  zephyr/lib/libc/picolibc/liblib__libc__picolibc.a  zephyr/lib/libc/common/liblib__libc__common.a  zephyr/lib/net_buf/liblib__net_buf.a  zephyr/soc/soc/nrf52840/libsoc__nordic.a  zephyr/subsys/bluetooth/common/libsubsys__bluetooth__common.a  zephyr/subsys/bluetooth/host/libsubsys__bluetooth__host.a  zephyr/drivers/clock_control/libdrivers__clock_control.a  zephyr/drivers/gpio/libdrivers__gpio.a  zephyr/drivers/pinctrl/libdrivers__pinctrl.a  zephyr/drivers/serial/libdrivers__serial.a  zephyr/drivers/timer/libdrivers__timer.a  modules/hal_nordic/nrfx/libmodules__hal_nordic__nrfx.a  modules/segger/libmodules__segger.a  -Wl,--no-whole-archive  zephyr/kernel/libkernel.a  -L/Users/samantha.cho/clones/zephyrproject/build/zephyr  zephyr/arch/common/libisr_tables.a  -mcpu=cortex-m4  -mthumb  -mabi=aapcs  -mfp16-format=ieee  -mtp=soft  -fuse-ld=bfd  -Wl,--gc-sections  -Wl,--build-id=none  -Wl,--sort-common=descending  -Wl,--sort-section=alignment  -Wl,-u,_OffsetAbsSyms  -Wl,-u,_ConfigAbsSyms  -nostdlib  -static  -Wl,-X  -Wl,-N  -Wl,--orphan-handling=warn  -Wl,-no-pie  -specs=picolibc.specs  -DPICOLIBC_LONG_LONG_PRINTF_SCANF -L"/Users/samantha.cho/zephyr-sdk-0.17.0/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.2.0/thumb/v7e-m/nofp" -lc -lgcc && cd /Users/samantha.cho/clones/zephyrproject/build/zephyr && /opt/homebrew/Cellar/cmake/3.30.5/bin/cmake -E true
/Users/samantha.cho/zephyr-sdk-0.17.0/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.2.0/../../../../arm-zephyr-eabi/bin/ld.bfd: zephyr/subsys/bluetooth/host/libsubsys__bluetooth__host.a(hci_raw.c.obj):/Users/samantha.cho/clones/zephyrproject/zephyr/subsys/bluetooth/host/hci_raw.c:60: undefined reference to `__device_dts_ord_133'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

[Vidar Berg]

Hello,

btattach will not return when the device is successfully attached. Instead it will continue running to manage the connection with the HCI interface. You can open another terminal window or tab to use the interface. Alternatively, you can create a systemd service,etc to let btattach run in the background.

Best regards,

Vidar

[samanthacho]

Hi,

I believe the device is not running -- I don't see the hci init being called when adding a breakpoint via gdb, and on my host device, I see the device being reported as down. Is disabling the config CONFIG_BT_CTLR on the Zephyr device necessary, as suggested by the HCI UART instructions, and if so, how do I resolve the build failures seen when disabling it for the sample?

```

root@7f0311c2-29f3-400f-89ff-27f9b285608a:~# hciconfig
hci0: Type: Primary Bus: UART
BD Address: 00:00:00:00:00:00 ACL MTU: 0:0 SCO MTU: 0:0
DOWN
RX bytes:0 acl:0 sco:0 events:0 errors:0
TX bytes:4 acl:0 sco:0 commands:1 errors:0

```

[Vidar Berg]

Hi,

The CONFIG_BT_CTLR symbol must be enabled in the build, as this configuration includes the Bluetooth controller. The instructions for disabling CONFIG_BT_CTLR apply if you plan to connect another board with the Zephyr host to your board, instead of using the BlueZ host on your Linux system.

After attaching the HCI interface, open another terminal and run $ sudo btmgmt --index 1, then issue the 'power on' command to initialize the interface. If this doesn't work, please run 'btmon' and repeat the steps to see if any errors are reported.

[samanthacho]

Hi,

After initiating the `power on` command via btmgmt, it fails with an invalid index error:
```

[hci0]# power on
Set Powered for hci1 failed with status 0x11 (Invalid Index)

```

btmon logs don't seem too informative, just reporting the same error:

```

@ MGMT Open: btmon (privileged) version 1.14 {0x0002} 0.368619
@ MGMT Command: Set Powered (0x0005) plen 1 {0x0001} [hci0] 3.136329
Powered: Enabled (0x01)
@ MGMT Event: Command Status (0x0002) plen 3 {0x0001} [hci0] 3.136349
Set Powered (0x0005)
Status: Invalid Index (0x11)
@ MGMT Close: btmgmt

```

[samanthacho]

when looking at the backtrace from gdb, it looks like the hci_uart_init is not being called, and the device is not moving past the PRE_KERNEL_2 stage:

```

arch_cpu_atomic_idle (key=key@entry=32) at /Users/samantha.cho/clones/zephyrproject/zephyr/arch/arm/core/cortex_m/cpu_idle.c:136
136 arch_irq_unlock(key);
(gdb) bt
#0 arch_cpu_atomic_idle (key=key@entry=32) at /Users/samantha.cho/clones/zephyrproject/zephyr/arch/arm/core/cortex_m/cpu_idle.c:136
#1 0x0001648a in k_cpu_atomic_idle (key=32) at /Users/samantha.cho/clones/zephyrproject/zephyr/include/zephyr/kernel.h:6017
#2 lfclk_spinwait (mode=CLOCK_CONTROL_NRF_LF_START_STABLE) at /Users/samantha.cho/clones/zephyrproject/zephyr/drivers/clock_control/clock_control_nrf.c:515
#3 z_nrf_clock_control_lf_on (start_mode=start_mode@entry=CLOCK_CONTROL_NRF_LF_START_STABLE) at /Users/samantha.cho/clones/zephyrproject/zephyr/drivers/clock_control/clock_control_nrf.c:571
#4 0x000173ac in sys_clock_driver_init () at /Users/samantha.cho/clones/zephyrproject/zephyr/drivers/timer/nrf_rtc_timer.c:766
#5 0x00018242 in z_sys_init_run_level (level=level@entry=INIT_LEVEL_PRE_KERNEL_2) at /Users/samantha.cho/clones/zephyrproject/zephyr/kernel/init.c:371
#6 0x0001840a in z_cstart () at /Users/samantha.cho/clones/zephyrproject/zephyr/kernel/init.c:779
#7 0x00003ab4 in z_prep_c () at /Users/samantha.cho/clones/zephyrproject/zephyr/arch/arm/core/cortex_m/prep_c.c:209
#8 0x000038fe in z_arm_reset () at /Users/samantha.cho/clones/zephyrproject/zephyr/arch/arm/core/cortex_m/reset.S:169
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

```

I also added a breakpoint to the hci_uart_init, and don't see it being called. Is there something needed to make the chip move into the application stage?

[samanthacho]

By commenting out `z_nrf_clock_control_lf_on` in `zephyr/drivers/timer/nrf_rtc_timer.c`, the device moves into the application stage, and I see the uart init function being called. However, the device is still down and cannot be communicated with.

```

 btattach -B /dev/ttyMSM2 -S 1000000 -P h4 &

```

```

root@7f0311c2-29f3-400f-89ff-27f9b285608a:~# hciconfig
hci0: Type: Primary Bus: UART
BD Address: 00:00:00:00:00:00 ACL MTU: 0:0 SCO MTU: 0:0
DOWN
RX bytes:0 acl:0 sco:0 events:0 errors:0
TX bytes:4 acl:0 sco:0 commands:1 errors:0

```

When I initiate from the host device (running bluez) the `btattach` command, or an `hciconfig hci0 up`, I see `bt_uart_isr` being called on the device, but the host device eventually reports the command times out 
```

root:~# hciconfig hci0 up
Can't init device hci0: Connection timed out (110)

```