Registers initial values with Altera Stratix II

Hi,

I've been using X FPGA for years and I often use the following VHDL initial value assignment, especially for finite state machines, counters, etc :

signal sCounter : std_logic_vector(7 downto 0) := x"1B";

Using "FPGA Editor", I'm able to validate that the synthesis tool has correctly interpreted the initial value by checking individual slice FF (INIT0, INIT1).

Now, my problem. Not having much experience with A Stratix II FPGA, I'm a little confused about how the synthesis and fitter tools use the initial value assignment. Quartus has a synthesis option of "Power-up Don't Care" that can be turned off. Does that means that FF must be initialized using the Assignment Editor using "Power-Up Level" attribute? RTFM didn't help (Quartus II 6.1 Handbook, Stratix II Device Handbook). Also, I tried to check the result with "Chip Editor" but the FF power-up values are not indicated (or I simply don't know how to show them) so I can't validate power-up conditions. For the moment, I don't have access to the hardware (else I would have already made a simple test to check that issue).

Anyone has a hint about how Quartus Synthesis handle initial values assignments?

Thanks!

Reply to
Francois Choquette
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Hello Francois,

Please refer him to the Chapter 8, Page 46 of the Quartus II 6.1 Handbook. In short, Quartus will honor initial or default values in VHDL, except for state machines. For an FSM with an asynchronous reset, it will use the asynchronous reset state as the power-up state. In the absence of an asynchronous reset, we use the first state in the enumerated type, or the state that was assigned the encoding "000..0" with a syn_encoding attribute.

You can verify power-up settings by looking for inverted registers in the report file It is in the Analysis and Synthesis section under Register Statistics. If a register must power-up to one, Quartus will use not-gate pushback to achieve the effect because all device registers in Stratix, Cyclone, Stratix II, etc power up to zero.

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Hope this helps, Subroto Datta Altera Corp.

Reply to
Subroto Datta

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