stm32: Add Zephyr BLE build variant for PYBD_SF6.

Add Zephyr BLE variant configuration for PYBD_SF6 board, with HCI UART
readpacket support for bulk reading from the BT coprocessor.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

Author: pi-anl

ports/stm32/boards/PYBD_SF6/mpconfigvariant_zephyr_ble.mk

@@ -0,0 +1,13 @@
+# Zephyr BLE variant for PYBD_SF6
+# Swaps NimBLE host stack for Zephyr BLE host, using same CYW43 UART HCI transport.
+
+# Enable Bluetooth with Zephyr stack (disable NimBLE default)
+MICROPY_PY_BLUETOOTH = 1
+MICROPY_BLUETOOTH_NIMBLE = 0
+MICROPY_BLUETOOTH_ZEPHYR = 1
+
+# Use bump allocator for GATT structures (STM32 port uses -nostdlib, no libc malloc)
+CFLAGS += -DMICROPY_BLUETOOTH_ZEPHYR_GATT_POOL=1
+
+# Force linker to keep HCI device symbols (prevent --gc-sections from removing them)
+LDFLAGS += -Wl,--undefined=__device_dts_ord_0 -Wl,--undefined=mp_bluetooth_zephyr_hci_dev

ports/stm32/mpbthciport.c

@@ -251,6 +251,18 @@ int mp_bluetooth_hci_uart_readchar(void) {
     }
 }
 
+int mp_bluetooth_hci_uart_readpacket(mp_bluetooth_hci_uart_readchar_t handler) {
+    // Read all available bytes from UART and feed to the H:4 parser callback.
+    // Returns total bytes read, or -1 if no data available.
+    int total = 0;
+    while (uart_rx_any(&mp_bluetooth_hci_uart_obj)) {
+        uint8_t chr = uart_rx_char(&mp_bluetooth_hci_uart_obj);
+        handler(chr);
+        total++;
+    }
+    return (total > 0) ? total : -1;
+}
+
 #endif // defined(STM32WB)
 
 // Default (weak) implementation of the HCI controller interface.