only use full_buffer for i2c.write(). Split SPI write into two instea…

…d of concat. Add multibyte address test.

adafruit_register/register_accessor.py

@@ -105,7 +105,8 @@ def write_register(
         self._pack_address_into_buffer(address)
         self._shift_rw_cmd_bit_into_first_byte(0)
         with self.spi_device as spi:
-            spi.write(self.address_buffer + buffer)
+            spi.write(self.address_buffer)
+            spi.write(buffer)
 
 
 class I2CRegisterAccessor(RegisterAccessor):
@@ -121,8 +122,7 @@ def __init__(self, i2c_device: I2CDevice, address_width: int = 1, lsb_first=True
         super().__init__(address_width, lsb_first)
         self.i2c_device = i2c_device
 
-        # buffer that will hold address + data for write_then_readinto operations
-        # will grow as needed
+        # buffer that will hold address + data for write operations, will grow as needed
         self._full_buffer = bytearray(address_width + 1)
 
     def read_register(self, address: int, buffer: bytearray):
@@ -134,23 +134,10 @@ def read_register(self, address: int, buffer: bytearray):
           Buffer must be long enough to be read all data sent by the device.
         :return: None
         """
-        if self.address_width + len(buffer) > len(self._full_buffer):
-            self._full_buffer = bytearray(self.address_width + len(buffer))
 
         self._pack_address_into_buffer(address)
-        for i in range(self.address_width):
-            self._full_buffer[i] = self.address_buffer[i]
-
         with self.i2c_device as i2c:
-            i2c.write_then_readinto(
-                self._full_buffer,
-                self._full_buffer,
-                out_end=self.address_width,
-                in_start=self.address_width,
-            )
-        # copy data from _full_buffer into buffer
-        for i in range(len(buffer)):
-            buffer[i] = self._full_buffer[self.address_width + i]
+            i2c.write_then_readinto(self.address_buffer, buffer)
 
     def write_register(self, address: int, buffer: bytearray):
         """
@@ -161,6 +148,18 @@ def write_register(self, address: int, buffer: bytearray):
 
         :return: None
         """
+        # grow full buffer if needed
+        if self.address_width + len(buffer) > len(self._full_buffer):
+            self._full_buffer = bytearray(self.address_width + len(buffer))
+
+        # put address into full buffer
         self._pack_address_into_buffer(address)
+        for i in range(self.address_width):
+            self._full_buffer[i] = self.address_buffer[i]
+
+        # put data into full buffer
+        for i, b in enumerate(buffer):
+            self._full_buffer[i + self.address_width] = b
+
         with self.i2c_device as i2c:
-            i2c.write(self.address_buffer + buffer)
+            i2c.write(self._full_buffer)

examples/register_accessor_multibyte_address_test.py

@@ -0,0 +1,42 @@
+# SPDX-FileCopyrightText: 2025 Tim Cocks for Adafruit Industries
+# SPDX-License-Identifier: MIT
+"""
+Verify functionality of multibyte address registers.
+
+Rrequires OV5640 camera connected.
+Default pins are for RPi Pico + Adafruit PiCowbell Camera Breakout
+"""
+
+import board
+import busio
+import digitalio
+from adafruit_bus_device.i2c_device import I2CDevice
+
+from adafruit_register.register_accessor import I2CRegisterAccessor
+from adafruit_register.register_bits import ROBits
+
+I2C_ADDRESS = 0x3C
+REG_CHIP_ID_HIGH = 0x300A
+
+
+class OV5640Tester:
+    chip_id = ROBits(16, REG_CHIP_ID_HIGH, 0, register_width=2, lsb_first=False)
+
+    def __init__(self, i2c):
+        try:
+            i2c_device = I2CDevice(i2c, I2C_ADDRESS)
+            self.register_accessor = I2CRegisterAccessor(
+                i2c_device, address_width=2, lsb_first=False
+            )
+        except ValueError:
+            raise ValueError(f"No I2C device found.")
+
+
+if __name__ == "__main__":
+    print("construct bus")
+    i2c = busio.I2C(board.GP5, board.GP4)
+    print("construct camera")
+    reset = digitalio.DigitalInOut(board.GP14)
+
+    ov5640 = OV5640Tester(i2c)
+    print(hex(ov5640.chip_id))