output doesn't toggle when simulating with other entities in Modelsim

Hi, I'm working on a vhdl testbench to simulate the behaviour of an I2C bus. I started with an original code (written in verilog) that works, made some changes to it an simulate it's behaviour as a stand-alone module using the .do file:

Code:

# I2C HPS

add wave -noupdate -label hps_sclk /I2C_to_GPIO/hps_sclk

add wave -noupdate -label hps_sda /I2C_to_GPIO/hps_sda_i

add wave -noupdate -label hps_sda_o_e /I2C_to_GPIO/hps_sda_o_e

# parallel store

add wave -noupdate -label gpio_input_reg /I2C_to_GPIO/gpio_input_reg

add wave -noupdate -label exph_input_reg /I2C_to_GPIO/exph_input_reg

add wave -noupdate -label expl_input_reg /I2C_to_GPIO/expl_input_reg

# inputs

add wave -noupdate -label gpio_input /I2C_to_GPIO/gpio_input

add wave -noupdate -label exp_input /I2C_to_GPIO/exp_input

# read/write byte count

add wave -noupdate -label hps_data_count_rd /I2C_to_GPIO/hps_data_count

# parallel store

add wave -noupdate -label gpio_output_pre /I2C_to_GPIO/gpio_output_pre

add wave -noupdate -label exph_output_pre /I2C_to_GPIO/exph_output_pre

add wave -noupdate -label expl_output_pre /I2C_to_GPIO/expl_output_pre

# outputs

add wave -noupdate -label gpio_output /I2C_to_GPIO/gpio_output

add wave -noupdate -label exp_output /I2C_to_GPIO/exp_output

add wave -noupdate -label dc_pwren /I2C_to_GPIO/dc_pwren

# i2c hps flags

add wave -noupdate -label hps_read_oper /I2C_to_GPIO/hps_read_oper

add wave -noupdate -label hps_data_or_address /I2C_to_GPIO/hps_data_or_address

add wave -noupdate -label hps_done /I2C_to_GPIO/hps_done

add wave -noupdate -label ack_flag /I2C_to_GPIO/ack_flag

add wave -noupdate -label hps_count /I2C_to_GPIO/hps_count

add wave -noupdate -label hps_sda_is_ack /I2C_to_GPIO/hps_sda_is_ack

# clock

force -freeze sim:/I2C_to_GPIO/hps_sclk 1 25, 0 {75 ns} -r 100

force -drive sim:/I2C_to_GPIO/gpio_input 00100010 0

force -drive sim:/I2C_to_GPIO/exp_input 0110101100 0

#######################################################################

# write

#######################################################################

# start pulse high

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 25

run 50

# start 0

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0

run 150

# 1

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0

run 100

# 0 0

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0

run 200

# 1 1 1

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0

run 300

# write and wait ack

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0 -cancel 100

run 200

# 0 0

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0

run 200

# 1

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0

run 100

# 0 0 0

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0

run 300

# 1

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0

run 100

# 0 and wait ack

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0 -cancel 100

run 200

# 1 1 1 1

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0

run 400

# 0

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0

run 100

# 1

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0

run 100

# 0

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0

run 100

# 1 and wait ack

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0 -cancel 100

run 200

# 1

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0

run 100

# 0

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0

run 100

# 1

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0

run 100

# 0

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0

run 100

# 1 1

force -drive sim:/I2C_to_GPIO/hps_sda_i 1 0

run 200

# 0 0 and wait ack

force -drive sim:/I2C_to_GPIO/hps_sda_i 0 0 -cancel 200

run 2000

When using the module - do file combination, it seemed to be working properly, so I moved ahead and added an I2C master entity to the bus, added a stimulus entity and a test-bench for connecting the units:

Code:

-- I omitted definition and architecture.. --

begin

slave: I2C_to_GPIO port map (

hps_sda_i => sda,

hps_sda_o_e => sda_o_e,

hps_sclk => scl,

gpio_input => gpio_input,

gpio_output => gpio_output,

write_pulse => write_pulse,

exp_input => exp_input,

exp_output => exp_output,

dc_pwren => dc_pwren,

state => gpio_state ;) // had to add this output bc sda_o_e wouldn't toggle

master: i2c_master port map (

clk => clock,

reset_n => reset_n,

ena => ena,

addr => addr,

rw => rw,

data_wr => data_wr, -- data to write to slave

busy => busy,

data_rd => data_rd, -- data read from slave

ack_error => ack_error,

sda_i => sda,

scl => scl,

mem_present => mem_present);

stimulus_tb: stimulus port map (

clock => clock,

reset_n => reset_n,

ena => ena,

addr => addr,

rw => rw,

data_wr => data_wr,

scl => scl,

sda => sda,

sda_o_e => sda_o_e,

mem_present => mem_present,

start_reg => start,

cmd => cmd,

rst_n => reset);

end;

The problem when using the former, is that the output hps_sda_o_e from I2C_to_GPIO entity wasn't toggling, even when I run using break points to the lines were it should, I even disconnected it from stimulus' 'sda_o_e' to make sure that there was nothing driving it, toggle the logic of the output, but still no toggling.. Finally, I added the 'state' output and made state change to a unique value every time sda_o_e was supposed to toggle. Since state did change, I set hps_sda_o_e to be the msb from state and this did the trick, I include the proccess in I2C_to_GPIO.v were hps_sda_o_e is driven:

see attached for code and definition

I want to know if this behavior is due to something that I'm missing and what could I do to prevent it. Thanks in advance!