hydrafw: 1-wire: scan does not work with multiple devices

I bought a HydraBus a few days ago and started to play with it:

> show system
HydraFW (HydraBus) v0.9-beta-115-ge463bc7 2020-01-29
sysTime: 0x046b48aa.
cyclecounter: 0x00809116 cycles.
cyclecounter64: 0x0000000000809128 cycles.
10ms delay: 1680032 cycles.

MCU Info
DBGMCU_IDCODE:0x10076413
CPUID:        0x410FC241
Flash UID:    0x31001A 0x58535011 0x20383658
Flash Size:   1024KB

Kernel:       ChibiOS 5.1.0
Compiler:     GCC 4.9.3 20150529 (release) [ARM/embedded-4_9-branch revision 227977]
Architecture: ARMv7E-M
Core Variant: Cortex-M4F
Port Info:    Advanced kernel mode
Platform:     STM32F405 High Performance with DSP and FPU
Board:        HydraBus 1.0
Build time:   Jan 29 2020 - 20:45:13

The firmware isn’t all up-to-date, but I don’t have the STM flasher available, so I probably cannot easily update it.

However, as the onewire code didn’t change since 2019, I experience issues with the scan command, which are probably still valid.

• Attached are two (original) DS1820 (no “S” version or anything newer), to +5V, Data, GND.
• Communication works, but only after pull up. Maybe that would be a more sensible default than floating?
• The scan command works with one DS1820 attached:

> 1-wire
Device: onewire1
GPIO resistor: floating
Bit order: LSB first
onewire1> pull up
onewire1> scan
Discovered devices : 10 54 D0 D3 00 08 00 A8 
onewire1> 

• …or the other:

onewire1> scan
Discovered devices : 10 D5 E9 D3 00 08 00 02 

• Attaching both DS1820 in parallel, it scans indefinitely until Reset/UBTN:

onewire1> scan
Discovered devices : 10 54 D0 D3 00 08 00 A8 
10 54 D0 D3 00 08 00 A8 
10 54 D0 D3 00 08 00 A8 
10 54 D0 D3 00 08 00 A8 
10 54 D0 D3 00 08 00 A8 
[...]

and only finds one of the two.

• Both DS1820 are working. I can (with only one attached) scan for both of them, and when both are attached, I can individually send them ROM_MATCH commands and let them sample a temperature or return their latest temperature reading.

I’d be willing to hack on this, but I would need to have a programmer, is that right? Flashing over USB or UART does not work?