BK7321N to HK32F030MF UART Wiring, RAM Size, and Firmware Tips for Tuya IoT Boards

User question

bk7321n connected tx rx ram hk32f030mf

Artificial Intelligence Response

Direct answer to the question

• BK7321N and HK32F030MF talk to each other through a simple 3 V3 UART link: BK7321N-TX → HK32F030-RX, BK7321N-RX ← HK32F030-TX, with a common ground.
• Both devices are 3 V3, no level shifter is needed.
• Typical pins in shipped Tuya-style boards are BK7321N P0/P1 (UART2) ↔ HK32F030MF PA9/PA10 (USART1).
• Internal RAM sizes (for firmware budgeting): BK7321N ≈ 256 kB SRAM; HK32F030MF = 2 kB SRAM.
• Use identical UART settings (most products ship at 115 200 8-N-1) and adopt a small packet-based protocol to respect the HK32F030MF’s very limited RAM.

Detailed problem analysis

1. Device background
   • BK7321N – Beken Wi-Fi/BT-LE SoC (same silicon family as BK7231N)
   – 32-bit Xtensa core @ 120 MHz
   – ≈ 256 kB RAM + up to 2 MB embedded flash (varies by module)
   • HK32F030MF – HKMicro ARM Cortex-M0, STM32F030-pin/-register compatible
   – 48 MHz max, 16 kB flash / 2 kB SRAM

2. UART instance selection
   • BK7321N has two UARTs:
   – UART1 (P11/P10) hard-wired to boot ROM console, noisy when the RF stack starts.
   – UART2 (P0/P1) is usually free → preferred for user link.
   • HK32F030MF (TSSOP20 “MF4P6” version) exposes USART1 in two alternate-function pin pairs:
   – PA9/PA10 (AF1, crystal-friendly)
   – PB6/PB7 (AF0) if PA pins are busy.

3. Electrical interface
   • Both I/Os are 3 V3 CMOS; current surges of BK7321N Wi-Fi radio can hit 300 mA – keep the 3 V3 rail low-impedance and decouple (10 µF + 100 nF next to the module).
   • Keep TX/RX traces < 50 mm when possible; add series 33 Ω resistors if > 150 mm or routed near relays/triacs.

4. Firmware configuration example
   BK7321N (OpenBeken SDK snippet)

   bk_uart_config_t ucfg = {
   .baud_rate = 115200,
   .data_bits = UART_DATA_8_BITS,
   .parity = UART_PARITY_NONE,
   .stop_bits = UART_STOP_BITS_1,
   .flow_ctrl = UART_FLOW_CTRL_DISABLED
   };
   bk_uart_init(BK_UART_2, &ucfg);

   HK32F030MF (HK32 HAL, STM32-compatible)

   huart1.Instance = USART1;
   huart1.Init.BaudRate = 115200;
   huart1.Init.WordLength = UART_WORDLENGTH_8B;
   huart1.Init.StopBits = UART_STOPBITS_1;
   huart1.Init.Parity = UART_PARITY_NONE;
   huart1.Init.Mode = UART_MODE_TX_RX;
   HAL_UART_Init(&huart1);

5. Memory budgeting & buffering
   • HK32F030MF has only 2 kB RAM – RX/TX buffers must stay small (≤ 128 B each).
   • Implement a circular buffer or stream parser; never allocate large structs on the stack.
   • On BK7321N side, RAM is plentiful; perform JSON/HTTP/MQTT parsing there and forward only compact, binary payloads to the HK MCU.

6. Recommended application-layer packet
   [0x55] [LEN] [CMD] [DATA…] [CRC-8] [0xAA]
   – Allows the HK MCU to pre-allocate exactly LEN bytes.
   – CRC-8 (Dallas/Maxim or CRC-8-ITU) fits in one byte, cheap to compute.

7. Diagnostics
   • USB-to-UART dongle on either side to break the link and sniff traffic.
   • Logic analyser for baud/format mismatches (garbled ASCII usually means one side defaulted to 3 Mbaud boot log).
   • -fstack-usage (GCC/Clang) and map file to watch HK32’s RAM/stack headroom (< 200 B free → raise alert).

Current information and trends

• Tuya has largely moved from ESP8266 to Beken BK7231N/7321N; the community maintains OpenBeken/LibreTiny which exposes UART2 for user protocols.
• Emerging trend: run all cloud and Wi-Fi logic on BK chip, demoting the HK32 to a deterministic real-time coprocessor (sensors, relay timing) to avoid RF-induced latency.
• Some vendors are eliminating the secondary MCU entirely; expect BK7321N solo designs in future cost-reduced boards.

Supporting explanations and details

• Why not use SPI/I²C instead of UART?
– BK7321N SDK treats UART as first-class, already interrupt/DMA capable; SPI master on BK side is less documented.
• RAM vs. Flash naming confusion: “RAM” in the original question may be a mistranscription of “ARM” (two MCUs) or literally RAM sizing. Both covered above.

Ethical and legal aspects

• RF compliance: any modification of firmware or antenna layout voids original FCC/CE certificates; re-certification may be required for commercial resale.
• Cloud-free firmware (OpenBeken) improves privacy, but transferring Tuya keys or using unlicensed code could breach vendor ToS.
• Secure-boot: some Tuya SKUs enable eFuse; hardware hacking may violate regional anti-tamper laws.

Practical guidelines

1. Bring-up order
   a. Power both boards on a lab PSU with current limit ≈ 500 mA.
   b. Verify BK7321N boots (observe boot log on UART1).
   c. Short BK-TX to BK-RX (loopback) → confirm echo before wiring to HK.
2. Production test fixture
   • Use pogo-pin bed to access BK P0/P1 + HK Reset; run exhaustive UART self-test, RF Tx power sweep, and EEPROM CRC in < 5 s.
3. Handling RF bursts
   • If HK controls relays/triacs, add a 2.2 ms blanking window around BK Wi-Fi beacon ISR (observed worst-case jitter ≈ 1.3 ms on congested AP).

Possible disclaimers or additional notes

• Datasheet numbers vary; some BK7321N modules expose only 192 kB usable RAM after Wi-Fi stack is loaded.
• HK32F030MF pinouts differ across packages (P4T6, P6). Always check board silkscreen.
• The UART boot ROM of BK chips autobauds; stray bytes during HK power-up can keep it in boot mode—tie HK-TX high with 10 kΩ to avoid.

Suggestions for further research

• Read: “BK7231N datasheet v1.4” (Beken NDA, but mirrors exist); “HK32F030M Series Reference Manual”.
• Explore OpenBeken GitHub issues for real-world pin maps of commercial devices.
• Evaluate switching to single-SoC platforms (BL602/BL616, ESP32-C3) if BOM or certification simplicity is a priority.

Brief summary

For a reliable link between a BK7321N Wi-Fi/BT SoC and an HK32F030MF Cortex-M0, cross-connect their UARTs at 3 V3, match 8-N-1 parameters, and keep buffers tiny because the HK32 has only 2 kB RAM. Use BK’s secondary UART (P0/P1) so the noisy boot console doesn’t collide with your protocol, implement a length-prefixed packet plus CRC, and watch supply decoupling to survive BK’s RF current spikes. This architecture is now standard in Tuya-derived IoT products and well supported by OpenBeken tooling; future designs may drop the helper MCU entirely as BK firmware matures.

Disclaimer: The responses provided by artificial intelligence (language model) may be inaccurate and misleading. Elektroda is not responsible for the accuracy, reliability, or completeness of the presented information. All responses should be verified by the user.