OVM Do Macros :

In order to create the user defined sequences

1. we need to create the sequence class which is derived from the ovm_sequence and specify the request and response parameters. 
2. User `ovm_sequence_utils macro's to associate the sequence with the relevant sequencer.
3. Implements to sequences body task which the scenario you want to execute.

In the body  task you can execute the sequence_item and other sequence with the ovm_do macros. A ovm_do macro translates in to following steps :

1. Wait till item is needed
2. Allocate using the factory
3. Randomize (with constraints or not)
4. Put on the consumer interface
5. Block code execution till item_done()

So essentially a ovm_do macro does the following things :

1. Create - Allocates and initializes the sequencer and parent sequence of the item or sequence.
2. Synchronize with sequencer - If the variable is an item, the item waits until the sequencer acknowledges that it can continue.
3. pre_do - Execute the pre_do() user hook of the sequence.
4. Randomize - Randomize the variable. If randomization fails, a warning is issued.
5. mid_do - Execute the mid_do() user hook of the sequence.
6. Post synchronization/body execution - If the variable is an item, the variable is provided to the sequencer, and the action waits until the item has been consumed.
   If the variable is a sequence, its body() method is executed.
7. post_do
   Execute the post_do() user hook of the sequence

OVM DO MACROS :

Main aim of these macros is the simplify the item and sequence execution

// ===========
// Syntax
// ===========
`ovm_*(variable)
`ovm_*_with(variable, { constraint-block} )

Variable must be derived from ovm_sequence_item or ovm_sequence.

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