I2C writeto_then_readfrom in a single transaction on u2if

src/adafruit_blinka/microcontroller/rp2040_u2if/rp2040_u2if.py

@@ -37,11 +37,13 @@ class RP2040_u2if:
     I2C0_WRITE = 0x82
     I2C0_READ = 0x83
     I2C0_WRITE_FROM_UART = 0x84
+    I2C0_WRITE_THEN_READ = 0x85
     I2C1_INIT = I2C0_INIT + 0x10
     I2C1_DEINIT = I2C0_DEINIT + 0x10
     I2C1_WRITE = I2C0_WRITE + 0x10
     I2C1_READ = I2C0_READ + 0x10
     I2C1_WRITE_FROM_UART = I2C0_WRITE_FROM_UART + 0x10
+    I2C1_WRITE_THEN_READ = I2C0_WRITE_THEN_READ + 0x10
 
     # SPI
     SPI0_INIT = 0x60
@@ -81,6 +83,8 @@ def __init__(self):
         self._neopixel_initialized = False
         self._uart_rx_buffer = None
 
+        self.FLAG_I2C_NO_WRITE_THEN_READ_AVAILABLE = False
+
     def _hid_xfer(self, report, response=True):
         """Perform HID Transfer"""
         # first byte is report ID, which =0
@@ -259,6 +263,38 @@ def _i2c_read(self, address, buffer, start=0, end=None):
         for i in range(read_size):
             buffer[start + i] = resp[i + 2]
 
+    def _i2c_write_then_read(
+        self, address, buffer_w, buffer_r, start_w=0, end_w=None, start_r=0, end_r=None
+    ):
+        """Write data to an address, then read data back and into the buffer"""
+        if self._i2c_index is None:
+            raise RuntimeError("I2C bus not initialized.")
+
+        end_w = end_w if end_w is not None else len(buffer_w)
+        end_r = end_r if end_r is not None else len(buffer_r)
+
+        write_then_read_cmd = (
+            self.I2C0_WRITE_THEN_READ
+            if self._i2c_index == 0
+            else self.I2C1_WRITE_THEN_READ
+        )
+
+        stop_flag = 0x01  # always stop
+
+        write_size = end_w - start_w
+        read_size = end_r - start_r
+
+        resp = self._hid_xfer(
+            bytes([write_then_read_cmd, address, stop_flag, write_size, read_size])
+            + buffer_w,
+            True,
+        )
+        if resp[1] != self.RESP_OK:
+            raise RuntimeError("I2C write_then_read error")
+        # move into buffer
+        for i in range(read_size):
+            buffer_r[start_r + i] = resp[i + 2]
+
     def i2c_writeto(self, address, buffer, *, start=0, end=None):
         """Write data from the buffer to an address"""
         self._i2c_write(address, buffer, start, end)
@@ -281,6 +317,25 @@ def i2c_writeto_then_readfrom(
         """Write data from buffer_out to an address and then
         read data from an address and into buffer_in
         """
+        if self._i2c_index is None:
+            raise RuntimeError("I2C bus not initialized.")
+
+        if not self.FLAG_I2C_NO_WRITE_THEN_READ_AVAILABLE:
+            try:
+                self._i2c_write_then_read(
+                    address,
+                    out_buffer,
+                    in_buffer,
+                    start_w=out_start,
+                    end_w=out_end,
+                    start_r=in_start,
+                    end_r=in_end,
+                )
+                return
+            except RuntimeError:
+                # Firmware may not support write_then_read; fall back
+                # to separate write + read for this and future calls.
+                self.FLAG_I2C_NO_WRITE_THEN_READ_AVAILABLE = True
         self._i2c_write(address, out_buffer, out_start, out_end, False)
         self._i2c_read(address, in_buffer, in_start, in_end)