Testbench description¶

Overview¶

The following figure depicts the Testbench:

Types¶

t_reg¶

A record type used to define register configurations for the testbench.

Constants¶

General constants¶

The following constants are defined:

Registers¶

The following registers are defined as t_reg:

Processes¶

Process p_check_uart_timings¶

Description¶

Verifies UART TX timings by transmitting test data 0x5555 and measuring bit durations.

Data Conversion:

• Test data 0x5555 contains four '5' characters
• Each '5' is converted to ASCII → 0x35 (binary: 00110101)

UART Frame Structure:

Each character is transmitted as a 10-bit frame:

[Start] [Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7] [Stop]
  0       1    0    1    0    1    1    0    0      1
          └─────────── LSB to MSB ───────────┘

The diagram below shows the waveform and which falling/rising edges are awaited:

In total, it is repeated four times.

Parameters¶

The process defines two variables:

Steps¶

1. Wait for the start of UART timings check

   • Wait for a rising edge on signal tb_check_uart_timings
   • Log info message: "Checking UART timings on TX with value 0x5555"

2. For each byte (1 to 4)

   • Wait for start bit
     • Wait for falling edge on tb_pad_o_uart_tx (a)
     • Set v_start_bit_time to current time
     • If first byte, set v_start_time to current time
   • Wait for a rising edge on signal tb_pad_o_uart_tx (b)
   • Check that (now - v_start_bit_time) is in time range C_UART_BIT_TIME ± C_UART_BIT_TIME_ACCURACY with procedure proc_check_time_in_range
   • Set v_start_bit_time to current time
   • Wait for a falling edge on signal tb_pad_o_uart_tx (c)
   • Check that (now - v_start_bit_time) is in time range C_UART_BIT_TIME ± C_UART_BIT_TIME_ACCURACY with procedure proc_check_time_in_range
   • Set v_start_bit_time to current time
   • Wait for a rising edge on signal tb_pad_o_uart_tx (d)
   • Check that (now - v_start_bit_time) is in time range C_UART_BIT_TIME ± C_UART_BIT_TIME_ACCURACY with procedure proc_check_time_in_range
   • Set v_start_bit_time to current time
   • Wait for a falling edge on signal tb_pad_o_uart_tx (e)
   • Check that (now - v_start_bit_time) is in time range C_UART_BIT_TIME ± C_UART_BIT_TIME_ACCURACY with procedure proc_check_time_in_range
   • Set v_start_bit_time to current time
   • Wait for a rising edge on signal tb_pad_o_uart_tx (f)
   • Check that (now - v_start_bit_time) is in time range C_UART_BIT_TIME ± C_UART_BIT_TIME_ACCURACY with procedure proc_check_time_in_range
   • Set v_start_bit_time to current time
   • Wait for a falling edge on signal tb_pad_o_uart_tx (g)
   • Check that (now - v_start_bit_time) is in time range 2. 0 * C_UART_BIT_TIME ± 2.0 * C_UART_BIT_TIME_ACCURACY with procedure proc_check_time_in_range
   • Set v_start_bit_time to current time
   • Wait for a rising edge on signal tb_pad_o_uart_tx (h)
   • Check that (now - v_start_bit_time) is in time range 2.0 * C_UART_BIT_TIME ± 2.0 * C_UART_BIT_TIME_ACCURACY with procedure proc_check_time_in_range
   • Set v_start_bit_time to current time

3. Verify total elapsed time

   • Check that (now - v_start_time) is in time range 9 * 4 C_UART_BIT_TIME ± C_UART_BIT_TIME_ACCURACY with procedure proc_check_time_in_range

Process p_check_spi_timings¶

Description¶

Verifies SPI clock timings.

Currently only verifies SPI clock timings.

The diagram below shows the waveform and which rising edges are awaited:

Parameters¶

The process defines two variables:

Steps¶

1. Wait for the start of SPI timings check

   • Wait for a rising edge on signal tb_check_spi_timings

2. For each bit (1 to 8)

   • Wait for a rising edge on signal tb_pad_o_sclk (a to h)
   • If first bit (bits = 1):
     • Set v_start_time to current time
     • Set v_start_bit_time to current time
   • Else:
     • Check that (now - v_start_bit_time) is in time range C_SPI_BIT_TIME ± C_SPI_BIT_TIME_ACCURACY with procedure proc_check_time_in_range
     • Set v_start_bit_time to current time

3. Verify total elapsed time

   • Check that (now - v_start_time) is in time range 7 * C_SPI_BIT_TIME ± 7 * C_SPI_BIT_TIME_ACCURACY with procedure proc_check_time_in_range

Process p_check_hsync_timings¶

Description¶

This process verifies the VGA horizontal synchronization (HSYNC) timing.

Parameters¶

The process defines two variables:

Steps¶

1. Wait for the start of HSYNC timings check

   • Wait for a rising edge on signal tb_check_hsync_timings

2. Measure HSYNC pulse width (sync pulse duration)

   • Wait for falling edge on tb_pad_o_vga_hsync (start of sync pulse)
   • Capture both v_start_time and v_start_bit_time as baseline
   • Wait for rising edge on tb_pad_o_vga_hsync (end of sync pulse)
   • Validate sync pulse duration against C_H_SYNC_PULSE_TIME ± C_H_SYNC_PULSE_TIME_ACCURACY
   • Update v_start_bit_time to current time

3. Measure HSYNC high period and total line time

   • Wait for next falling edge on tb_pad_o_vga_hsync (completion of one horizontal line)
   • Validate high period: Check time since last edge against C_H_HSYNC_HIGH_TIME ± C_H_HSYNC_HIGH_TIME_ACCURACY
   • Validate complete line time: Check time since initial v_start_time against C_H_WHOLE_LINE_TIME ± C_H_WHOLE_LINE_TIME_ACCURACY

Process p_check_vsync_timings¶

Description¶

This process verifies the VGA vertical synchronization (VSYNC) timing.

Parameters¶

The process defines two variables:

Steps¶

1. Wait for the start of HSYNC timings check

   • Wait for a rising edge on signal tb_check_vsync_timings

2. Measure HSYNC pulse width (sync pulse duration)

   • Wait for falling edge on tb_pad_o_vga_vsync (start of sync pulse)
   • Capture both v_start_time and v_start_bit_time as baseline
   • Wait for rising edge on tb_pad_o_vga_vsync (end of sync pulse)
   • Validate sync pulse duration against C_V_SYNC_PULSE_TIME ± C_V_SYNC_PULSE_TIME_ACCURACY
   • Update v_start_bit_time to current time

3. Measure HSYNC high period and total line time

   • Wait for next falling edge on tb_pad_o_vga_vsync
   • Validate high period: Check time since last edge against C_V_HSYNC_HIGH_TIME ± C_V_HSYNC_HIGH_TIME_ACCURACY
   • Validate complete frame time: Check time since initial v_start_time against C_V_WHOLE_LINE_TIME ± C_V_WHOLE_LINE_TIME_ACCURACY

Procedures¶

Procedure proc_check_time_in_range¶

Description¶

This procedure performs a range check to verify that time_to_check is within expected_time ± accuracy.

Parameters¶

Steps¶

1. Perform Range Check
   • Check that abs(time_to_check - expected_time) <= accuracy with procedure check

Procedure proc_reset_dut¶

Description¶

This procedure puts all the testbench signals into a known state.

Parameters¶

Steps¶

1. Reset the DUT by Setting Input State to All Zeros

   • Set tb_pad_i_rst_h to 1
   • Set tb_i_uart_select to 0
   • Set tb_i_uart_rx_manual to 0
   • Set tb_pad_i_switch_0 to 0
   • Set tb_pad_i_switch_1 to 0
   • Set tb_pad_i_switch_2 to 0
   • Set tb_i_read_address to 0x00
   • Set tb_i_read_address_valid to 0
   • Set tb_i_write_address to 0x00
   • Set tb_i_write_data to 0x0000
   • Set tb_i_write_valid to 0
   • Set tb_check_uart_timings to 0
   • Set tb_check_spi_timings to 0

2. Wait for the Specified Number of Clock Cycles

   • Wait for c_clock_cycles * C_CLK_PERIOD

3. De-assert Reset

   • Set tb_pad_i_rst_h to 0

4. Wait for the DUT to Settle

   • Wait for 5 ns

Procedure proc_uart_send_byte¶

Description¶

This procedure sends a byte via UART using the manually driven line.

Parameters¶

Steps¶

1. Ensure the Manual UART is Selected

   • If tb_i_uart_select = 0:
     • Set tb_i_uart_select to 1
     • Wait for 200 ns

2. Send the Start Bit

   • Set uart_rx to 0
   • Wait for C_UART_BIT_TIME

3. Send the Data Bits (LSB to MSB)

   • For bit_idx in byte_to_send'low to byte_to_send'high:
     • Set uart_rx to byte_to_send(bit_idx)
     • Wait for C_UART_BIT_TIME

4. Send the Stop Bit

   • Set uart_rx to 1
   • Wait for 1. 1 × C_UART_BIT_TIME

Procedure proc_uart_write¶

Description¶

This procedure writes a value to a specified UART register.

Parameters¶

Steps¶

1. Ensure the Model UART is Selected

   • If tb_i_uart_select = 1:
     • Set tb_i_uart_select to 0
     • Wait for 200 ns

2. Set Up the Write Operation

   • Set tb_i_write_address to reg.addr
   • Set tb_i_write_data to value
   • Set tb_i_write_valid to 1

3. Wait and De-assert the Valid Flag

   • Wait for 200 ns
   • Set tb_i_write_valid to 0

4. Wait for the Write Operation to Complete

   • Wait for 1.1 × C_UART_WRITE_CMD_TIME

Procedure proc_uart_read¶

Description¶

This procedure reads a value from a specified UART register.

Parameters¶

Steps¶

1. Ensure the Model UART is Selected

   • If tb_i_uart_select = 1:
     • Set tb_i_uart_select to 0
     • Wait for 200 ns

2. Wait Before Starting the Read

   • Wait for 500 ns (to avoid simulation stuck)

3. Set Up the Read Operation

   • Set tb_i_read_address to reg.addr
   • Set tb_i_read_address_valid to 1

4. Wait for the Read Operation to Complete

   • Wait for a rising edge on signal tb_o_read_data_valid

5. De-assert the Read Valid Signal

   • Set tb_i_read_address_valid to 0

Procedure proc_uart_check¶

Description¶

This procedure checks if the read value from a specified UART register matches the expected value.

Parameters¶

Steps¶

1. Read the Register Value

   • Read the register reg value with procedure proc_uart_read

2. Check the Returned Value

   • Check that the returned value tb_o_read_data equals expected_value with the procedure check_equal

Procedure proc_uart_check_default_value¶

Description¶

This procedure checks if the default value of a specified UART register matches the expected reset value.

Parameters¶

Steps¶

1. Check the Default Value Against the Register's Reset Value
   • Check that the value after reset is equal to the one specified in reg.data with the procedure proc_uart_check

Procedure proc_uart_check_read_only¶

Description¶

This procedure checks if a specified UART register is read-only by attempting to write to it and verifying that the value remains unchanged.

Parameters¶

Steps¶

1. Attempt to Write an Incorrect Value to the Register

   • Write the data not(reg.data) to the register address reg.addr with procedure proc_uart_write

2. Check if the Register Value Remains Unchanged

   • Read back the register and check if the register value remains unchanged with procedure proc_uart_check

Procedure proc_uart_check_read_write¶

Description¶

This procedure checks if a specified UART register is read-write by writing a value to it and verifying that the value is correctly updated.

Parameters¶

Steps¶

1. Write the Inverted Default Value to the Register

   • Write the data not(reg.data) to the register address reg.addr with procedure proc_uart_write

2. Check if the Register Value is Updated Correctly

   • Read back the register and check if the register value is matching expected_value with procedure proc_uart_check

Procedure proc_spi_write¶

Description¶

Writes a byte value to the SPI master module via UART register interface.

Parameters¶

Steps¶

1. Reset C_REG_SPI_TX for Rising Edge Detection

   • Write 0x0000 to register C_REG_SPI_TX with procedure proc_uart_write

2. Write the Data with Valid Flag Set

   • Write (7b0 & 1b1 & value) to the register C_REG_SPI_TX with procedure proc_uart_write

Procedure proc_spi_check¶

Description¶

Writes a value to SPI master and verifies correct transmission and reception.

Parameters¶

Steps¶

1. Write Data to SPI

   • Start an SPI transaction with procedure proc_spi_write

2. Retrieve Data from SPI Slave Stream

   • Pop data from C_SLAVE_STREAM into v_spi_slave_data (MOSI path verification)

3. Verify MOSI Path

   • Check that v_spi_slave_data equals value with procedure check_equal

4. Read and Verify MISO Register Data

   • Check that sampled SPI data from slave is matching the one decoded in the REG_SPI_RX register with procedure proc_uart_check