issue#2 - Testbench for I2C subsystem

[Juninho99]

issue#2 - Testbench for I2C subsystem

[Juninho99]

Regardless of how we attempted to assign values through cocotb simulation to the variables i2c_sda_di, i2c_scl_di, i2c_sda_do, or i2c_scl_do, which are connected to the IOBUF module, the value remained as determined by the RTL.

Various approaches such as Force, immediatevalue, and others were tried, but none were successful. Ultimately, we created an empty IOBUF module, which allowed setting values only on the I (input) ports, while the O (output) ports did not allow this.

All of these attempts were made using Verilator.

In the end, we switched to Icarus, which supports not only 0 and 1 but also 'X and 'Z, and there were absolutely no issues with the original IOBUF module or the I2C simulation.

[Juninho99]

We used the cocotbext-i2c library for simulating the slave device. In the Python script I2CDevice.py, it was necessary to add the following to the constructor:

#....before
def __init__(self, sda=None, sda_o=None, scl=None, scl_o=None, *args, **kwargs):
    self.log = logging.getLogger(f"cocotb.{sda._path}")
    self.sda = sda
    #......

#....after
def __init__(self, addr=None, sda=None, sda_o=None, scl=None, scl_o=None, *args, **kwargs):
    self.log = logging.getLogger(f"cocotb.{sda._path}")
    self.sda = sda
    self.addr = addr
    #.....

These changes were necessary for it to work properly. After making these modifications and running the cocotb simulation with the Icarus simulator, everything worked as expected. A testament to this is the successful write of 65 registers in the slave device.

[chili-chips-ba]

do we still need this?:

`ifdef COCOTB_SIM
   inout  tri1   i2c_sda,
   inout  tri1   i2c_scl,
`else
   inout  wire   i2c_sda,
   inout  wire   i2c_scl,
`endif //COCOTB_SIM

If cocoTB+Verilator cannot override O port of the dummy IOBUF, try doing this in the dummy IOBUF:

logic  O_from_coco;
assign O = O_from_coco;

then override O_from_coco, which is now an input.

[chili-chips-ba]

Also, look for all instances of COCOTB_SIM macro in RTL and try to remove them. Only if absolutely not possible, replace them with SIM_ONLY. The goal is to rationalize the use of macros, as they have global scope.