Update readme

Signed-off-by: Alex Forencich <[email protected]>

Author: alexforencich

README.md

@@ -3,6 +3,7 @@
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 GitHub repository: https://github.com/alexforencich/cocotbext-i2c
 
@@ -29,3 +30,72 @@ Installation for active development:
 
 See the `tests` directory, [taxi](https://github.com/fpganinja/taxi), and [verilog-i2c](https://github.com/alexforencich/verilog-i2c) for complete testbenches using these modules.
 
+### I2C Master
+
+The `I2cMaster` class can be used to issue read and write operations on an I2C bus.
+
+Example:
+
+    from cocotbext.i2c import I2cMaster
+
+    i2c_master = I2cMaster(dut.sda_i, dut.sda_o, dut.scl_i, dut.scl_o, 400e3)
+
+To issue I2C operations with an `I2cMaster`, call `read()` or `write()`.  These are the preferred methods, as they will manage the bus state automatically.  Lower-level methods must be called in the appropriate order.  The `read()` and `write()` methods will leave the bus active, so call `send_stop()` to release the bus.
+
+#### Constructor parameters:
+
+* _sda_: serial data in/out
+* _sda_o_: serial data output
+* _scl_: clock in/out
+* _scl_o_: clock output
+* _speed_: nominal data rate in bits per second (default `400e3`)
+
+#### Attributes:
+
+* _speed_: nominal data rate in bits per second
+
+#### Methods
+
+* `write(addr, data)`: send _data_ to device at address `addr` (blocking)
+* `read(addr, count)`: read _count_ bytes from device at address `addr`  (blocking)
+* `send_start()`: send a start condition on the bus
+* `send_stop()`: send a stop condition and release the bus
+* `send_byte()`: send a byte on the bus
+* `recv_byte()`: read a byte from the bus
+
+### I2C Device
+
+The `I2cDevice` class emulates an I2C device.  This class cannot be used directly, instead it should extended and the methods `handle_start()`, `handle_write()`, `handle_read()`, and `handle_stop()` implemented appropriately.  See `I2cMem` for an example.
+
+#### Constructor parameters:
+
+* _sda_: serial data in/out
+* _sda_o_: serial data output
+* _scl_: clock in/out
+* _scl_o_: clock output
+
+### I2C Memory
+
+The `I2cMemory` class emulates a simple memory like an I2C EEPROM.
+
+Example:
+
+    from cocotbext.i2c import I2cMemory
+
+    i2c_mem = I2cMemory(dut.sda_i, dut.sda_o, dut.scl_i, dut.scl_o, 0x50, 256)
+
+The memory can then be read/written via I2C operations on the bus, with the first bytes written after a start bit setting the address, and subsequent reads/writes advancing the internal address and reading/writing the memory.  The memory can also be accessed via `read_mem()` and `write_mem()`.
+
+#### Constructor parameters:
+
+* _sda_: serial data in/out
+* _sda_o_: serial data output
+* _scl_: clock in/out
+* _scl_o_: clock output
+* _addr_: device address (default `0x50`)
+* _size_: size in bytes (default `256`)
+
+#### Methods
+
+* `read_mem(addr, count)`: read _count_ bytes from memory, starting at `addr`
+* `write_mem(addr, data)`: write _data_ to memory, starting at `addr`