Re: [vhdl-200x] Records with diectional subtypes

Hi Peter,
I notice that Jim embedded his comments in the TWiki page. As I know not how
to do this, nor given my verbosity, do I think that I should be allowed
to ;-), I will limit myself to Emails.
My question is embedded below:
On 16/08/2012 21:07, Jim Lewis wrote:
> Hi Peter,
> In the Block Interface proposal, "Candidate: Records with diectional subtypes":
> http://www.eda-twiki.org/cgi-bin/view.cgi/P1076/BlockInterfaces#Candidate_Records_with_direction
>
>
> Can we extend this to also allow open in the subtype? The following slave does
> not use the "we" element (perhaps it is read only and never does a write):
>
> subtype t_slave is t_cpu_bus port(adr, dat, en : in; sdt, ack, err : out; we
> : open);
>
>
> Can we allow some ports to not use all elements?
>
> type t_cpu_bus is record
> adr : std_logic_vector(15 downto 0); --Address
> dat : std_logic_vector(15 downto 0); --Data from master to slave=
> we : std_logic; --Write enable from master=
> en : std_logic_(7 downto 0) ; --Enable from master=
> sdt : std_logic_vector(15 downto 0); --Data from slave to master=
> ack : std_logic; --Acknowledge from slave=
> err : std_logic; --Error from slave=
> end record;
>
> subtype t_master is t_cpu_bus port(adr, dat, we, en : out; sdt, ack, err : in);
>
> subtype t_slave is t_cpu_bus port(adr, dat, we, en(1) : in; sdt, ack, err :
> out ; en(7 downto 2), en(0) : open );
So if I want to instantiate the full 8 slaves (as per your example) would I need
8 separate subtype declarations?
subtype t_slave0 is t_cpu_bus port(adr, dat, we, en(0) : in; sdt, ack, err : out
; en(7 downto 1) : open );
subtype t_slave1 is t_cpu_bus port(adr, dat, we, en(1) : in; sdt, ack, err : out
; en(7 downto 2), en(0) : open );
...
subtype t_slave5 is t_cpu_bus port(adr, dat, we, en(5) : in; sdt, ack, err : out
; en(7 downto 6),
en(4 downto 0) : open );
...
subtype t_slave7 is t_cpu_bus port(adr, dat, we, en(7) : in; sdt, ack, err : out
; en(6 downto 0) : open );
or have I misunderstood how this is to work?
>
> Inside the slave is en seen as en(1) or just en? Is there a notation that
> allows just en?
>
> All questions also on the twiki page.
>
> Best,
> Jim

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Regards,
         Brent Hayhoe.
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