UV-K5 V3 emulator

Runs Quansheng UV-K5 V3 / UV-K1 firmware on a PC. The radio uses a Puya PY32F071 (Cortex-M0+), which QEMU has no machine for, so this adds one.

The firmware boots to its main loop in about five seconds, the LCD contents are readable, and the keypad drives the menus. See Status for what is and is not modelled.

Main screen	Menu	Navigated with keys

Real captures, not mock-ups: tools/screenshot.py reads the firmware's gFrameBuffer out of guest memory and renders it, so these are the pixels the LCD driver actually wrote. Left to right: the dual-watch main screen, the menu opened with key.py MENU (entry 01/79, Step), and 03/79 after key.py DOWN DOWN.

What it is for

Editing firmware and reflashing a radio to test one line is slow, and some bugs are invisible from the outside. A recent example: CW macro recording appeared to do nothing, and the cause was three layers down -- the keyer was being torn down by a later call that recomputed its state from the wrong VFO. On hardware you see "nothing happens"; here you can read the actual variables.

What it does not do is model radio behaviour. It reproduces what the firmware commanded -- frequency, power step, carrier keying in time -- not the analogue result. Keying envelopes, spurious emissions and sensitivity need a real radio and a spectrum analyser. That is not a gap to be closed later; the transceiver chip has no public datasheet, so its driver is the only specification available.

Status

Area	State
Boot to main loop	works, ~5 s
LCD contents	readable via tools/screenshot.py
SPI flash, settings, calibration	works, and persists across power cycles
Frequency entry	works, stored per band and kept
Keypad and menu navigation	works, including waking from power save
Serial output (firmware log)	works, appears in the web UI log
Serial input, CPS programming protocol	works, -serial any chardev
BK4819 register interface	works, RSSI and status readable
Timing accuracy	deliberately wrong, see Timing
Analogue RF behaviour	not modelled and never will be, see AGENTS.md

A short tools/key.py MENU opens the menu, UP/DOWN move through it, MENU enters a submenu, and typing a menu number jumps straight to that entry. Press duration decides short versus held, which the firmware treats as different events -- see Timing.

Press duration is the thing to get right. A hold of 400 ms or more is a long press, and handlers act on it differently: MAIN_Key_MENU opens the menu on a short release and does nothing on the hold path. If a key seems ignored, shorten the press rather than lengthening it. Waking from power save needs nothing special -- one 200 ms press both wakes the radio and opens the menu, verified after 45 s of idle.

tools/keypad_test.py checks all of this against a throwaway QEMU instance. It exists because the keypad has one non-obvious trap: the keypad model's row_out array must stay volatile, or GCC at -O2 proves the lines are still NULL and deletes every call to keypad_update_rows(), so no row is ever driven and keypresses silently stop working. Run the test after touching that code; AGENTS.md has the object-code evidence.

Layout

qemu/                    QEMU sources to be copied into a QEMU tree
  py32f071.c             the SoC and machine (the bulk of the work)
  armv7m_systick.*.patched  SysTick with the poll-boost property added
assets/                  flash.img, plus pristine/ as the reference copy
  calibration.bin        512-byte dump from a real radio
deploy/                  nginx vhost for the HTTPS front end
docs/reverse-proxy.md    how https://k6v3.mckero.dn42/ is served
docs/screenshots/        LCD captures used in this README
tools/                   run, screenshot, inject keys, probe state
  keypad_test.py         keypad regression test, boots its own instance
  test_flash_persist.py  flash writes survive a power cycle
  test_freq_entry.py     a typed frequency takes effect and persists
  test_serial_rx.py      the firmware answers programming commands
  test_bk4819.py         BK4819 register interface, RSSI not stuck at zero
  test_bk4819_readback.sh  register reads come back bit-aligned
  lib_kill_emulator.sh   cleanup that only ever kills emulators
  webui.py               web remote control: live LCD plus clickable keypad
  dn42_firewall.sh       restrict the web UI port to DN42 sources
  restore_flash.sh       roll the flash image back to its pristine state
  uvk5_qmp.py            QMP client
  uvk5_lcd.py            framebuffer decode, PNG encode, frame grabber
  uvk5_keys.py           key names the keypad model accepts
harness/, stubs/, shim/, tests/   host build of the CW timing chain (stage A)

Building

Needs a QEMU 7.2 source tree, meson, ninja, libfdt-dev, libglib2.0-dev, libpixman-1-dev.

# 1. Drop the sources into a QEMU tree
cp qemu/py32f071.c                   $QEMU/hw/arm/
cp qemu/armv7m_systick.c.patched     $QEMU/hw/timer/armv7m_systick.c
cp qemu/armv7m_systick.h.patched     $QEMU/include/hw/timer/armv7m_systick.h

# 2. Register the machine. In $QEMU/hw/arm/Kconfig:
#      config UVK5_V3
#          bool
#          default y
#          depends on TCG && ARM
#          select PY32F071_SOC
#      config PY32F071_SOC
#          bool
#          select ARM_V7M
#          select UNIMP
#    In $QEMU/hw/arm/meson.build:
#      arm_ss.add(when: 'CONFIG_UVK5_V3', if_true: files('py32f071.c'))

# 3. Build just the ARM target
cd $QEMU
./configure --target-list=arm-softmmu --disable-docs --disable-tools
cd build && ninja qemu-system-arm

Then check the build actually works, which takes about a minute:

python3 tools/keypad_test.py
python3 tools/test_flash_persist.py
python3 tools/test_freq_entry.py
python3 tools/test_serial_rx.py
python3 tools/test_bk4819.py
bash tools/test_bk4819_readback.sh

This matters more than it looks. The keypad can break silently under -O2 without any compiler warning -- see the volatile note in Status -- so a clean build is not evidence that keypresses work. The other two cover the flash path, where four separate faults each ended up zeroing stored frequencies without producing any error: details in AGENTS.md.

The rest of the tests:

cd tools && python3 -m unittest discover -p 'test_uvk5*.py' -v  # fast, no emulator
cd tools && python3 -m unittest test_webui -v                   # fast, no emulator
python3 tools/test_webui_e2e.py                                # boots its own emulator

Running

python3 tools/make_flash.py     # once, builds assets/flash.img

The emulator writes to that image, so a session can leave edited settings or a damaged EEPROM behind. assets/pristine/ holds a checksummed copy of the image as first generated, and tools/restore_flash.sh puts it back:

tools/restore_flash.sh --verify   # is the reference copy itself intact
tools/restore_flash.sh --diff     # has the live image changed, and by how much
tools/restore_flash.sh            # restore, saving the current image first

The reference copy is stored gzipped, which takes 2.3 KiB rather than 2 MiB because the image is nearly all 0xFF, so it is small enough to keep in git. The live image stays ignored: it is a build artifact that gets written to.

tools/run.sh                    # starts the machine

tools/where.sh                  # where the firmware is executing
python3 tools/screenshot.py --frame-addr 0x200013DC \
    --status-addr 0x2000175C --port 1234 --out screen.png
python3 tools/key.py MENU       # inject a keypress
tools/gpiob_dump.sh             # GPIOB registers

The machine exposes a GDB stub on port 1234 and a QMP socket at /tmp/uvk5-qmp.sock. It is headless: the screen is read out of guest memory rather than drawn, so no display backend is needed.

Screenshots need the addresses of gFrameBuffer and gStatusLine, which move between builds. Find them with:

arm-none-eabi-nm firmware.elf | grep -E 'gFrameBuffer|gStatusLine'

Web remote control

tools/webui.py serves the LCD and a clickable keypad, so the radio can be driven from a browser instead of key.py plus screenshot.py.

tools/run.sh                                   # emulator first
python3 tools/webui.py --frame-addr 0x200013DC \
    --status-addr 0x2000175C                   # then the server

Open http://127.0.0.1:8080/. The keypad is laid out like the radio, with the side keys alongside. Arrow keys, Enter (MENU), Esc (EXIT) and the digits are bound to the physical keys.

Press duration comes from how long you actually hold the button, because the firmware treats anything past 400 ms as a held key and dispatches it as a different event. The browser sends the two edges separately rather than asking the server for a fixed-length press.

Endpoints, if you want to script it:

Route	Purpose
GET /	the page
GET /stream	multipart PNG stream, up to 15 fps
GET /frame.png	one frame
POST /api/key	{"key": "MENU", "action": "down"} — also up or tap
POST /api/release-all	release every key, if one ever sticks
GET /api/status	QMP query-status

Frames are read with QMP memsave, about 1.35 ms each, and the guest keeps running throughout. Two details there are easy to get wrong:

• memsave, not pmemsave. The framebuffer symbols are CPU virtual addresses. pmemsave treats its argument as physical and returns a block of zeros, so the screen renders blank with no error anywhere.
• Not gdb. screenshot.py reads frames through gdb, which halts the guest on every attach. That is unusable for a live stream and it also perturbs key debounce timing.

Two constraints worth knowing before you use it:

• The QMP socket takes one client. While the server is up, tools/key.py cannot talk to the same emulator.
• There is no authentication. Anyone who reaches the port has full control of the emulated radio. It binds loopback by default for that reason.

Reaching it from elsewhere

The deployment here runs the server on loopback and puts nginx in front of it for TLS, at https://k6v3.mckero.dn42/. See docs/reverse-proxy.md for the vhost, including the two settings that matter for this app: proxy_buffering off (or the frame stream arrives in bursts) and X-Forwarded-For (or every log line is attributed to 127.0.0.1).

Binding directly with --host :: also works, but with no authentication the port then has to be filtered by source address. tools/dn42_firewall.sh restricts it to DN42:

tools/dn42_firewall.sh apply 8080     # DN42 + loopback only
tools/dn42_firewall.sh show  8080     # rules and packet counts
tools/dn42_firewall.sh remove 8080

One detail that is easy to get wrong: this host's INPUT policy is ACCEPT, so a rule that only allows DN42 changes nothing -- the port is already reachable with no rules at all. The rule that does the work is the final DROP. Verify by watching the counters rather than by assuming:

tools/dn42_firewall.sh show 8080
# a rising DROP count means non-DN42 traffic is actually being rejected

The rules do not survive a reboot. Re-run apply, or persist them with iptables-persistent.

There is no PTT button: the keypad model has no PTT line, so the press property rejects the name. Unknown keys are rejected with 400 rather than forwarded.

How the machine is put together

Register layouts come from the vendor CMSIS header shipped with the firmware (Drivers/CMSIS/Device/PY32F071/Include/py32f071xB.h), not from guesswork.

FLASH  0x08000000  128 KB   application at +0x2800, bootloader below it
SRAM   0x20000000   16 KB
RCC    0x40021000
GPIO   0x50000000   ports A, B, C, F at 0x400 intervals
SPI1   0x40013000   display
SPI2   0x40003800   flash
ADC1   0x40012400

Modelled: RCC, GPIO, ADC, both SPI controllers, DMA1, and the PY25Q16 flash. Everything else answers through a logging catch-all — the log is how the next thing worth modelling gets identified.

Seven things had to be right before the firmware would boot, each found by watching where it stopped:

• Flash alias at the application offset. The core fetches its vector table from address 0, and the image loads at 0x08002800, so 0 has to alias there and not at the flash base.
• Clock ready bits. BOARD_Init polls them; each enable bit is mirrored into its ready bit.
• ADC calibration. CR2.CAL is write-1-to-start and hardware-cleared, so it must never be stored set or the wait loop never exits.
• SPI flags. Transfers complete inside the register write, so TXE stays asserted and RXNE is raised by the write.
• DMA. The flash driver never touches the SPI data register — it arms channels 4 and 5, enables the transfer-complete interrupt and spins on a flag its ISR sets.
• SysTick. See below.
• Transceiver data line. RADIO_SetupRegisters waits for bit 0 of the BK4819 REG_0C to clear. The bus is bit-banged over GPIO, so PB9 idles low until that bus has a real model, making reads return zero.

Timing

SYSTICK_DelayUs polls the SysTick counter and accumulates differences. On hardware each loop iteration advances the counter by tens of ticks; under emulation a register read costs far more relative to guest time, so the counter barely moves per read. Measured: a 120 ms delay advanced 832 of 5,760,000 required ticks in four seconds — about 7.7 hours to complete.

Lowering the clock does not help, which is worth knowing before trying it: the bottleneck is loop iterations per second, not counter speed. Dropping 48 MHz to 200 Hz gained only 32x.

What works is reporting a counter value that runs ahead of the real one, growing with every read. The poll-boost property on SysTick does that. Two earlier attempts wrote the value back into the timer instead, which made each read re-anchor the count — the reported value stopped changing, the firmware's if (cur != prev) guard never fired, and the loop hung outright.

The consequence is that guest time runs fast during any delay. Fine for exercising menus and control flow; wrong for judging signal timing.

poll-boost accelerates counter reads only. SysTick interrupts still fire at close to real time, and those are what drive SysTick_Handler -> gNextTimeslice -> APP_TimeSlice10ms -> CheckKeys. So the firmware's 10 ms timeslice thresholds hold in wall clock: a key must be down for 20 ms to register and 400 ms makes it a long press.

Keeping those two apart matters. tools/key.py originally held keys for 2500 ms on the assumption that guest time ran fast here too, which turned every press into a long press. Handlers that act on a short release — MAIN_Key_MENU among them — ignored all of it, and the keypad looked broken when it was not.

Stage A: the CW timing chain on the host

harness/, stubs/, shim/ and tests/ compile app/cwkeyer.c and app/cwmacro.c unmodified against stub drivers, with a virtual clock and scripted paddle input. Feed a timeline of contact closures, assert on the decoded characters and element durations.

Firmware sources are compiled as-is on purpose. Editing them to make them build on a host would let the tests drift from what the radio runs. The debounce in CW_ReadKeys is transcribed rather than stubbed, because its asymmetry (three consecutive reads to register a press, immediate release) is part of the timing behaviour under test.

Licence

Apache 2.0, see LICENSE.

One exception: qemu/py32f071.c is licensed GPL-2.0-or-later, as its header states. It is built into QEMU and derives from QEMU's device models, which are GPL-2.0, so it cannot be anything else. The tools, harness and documentation are Apache 2.0.

Credits

Base firmware: armel/uv-k1-k5v3-firmware-custom. Register definitions from the vendor CMSIS headers.