I created a set of schematics for the sky130 `gpiov2` cell LVS. Feel free to post PR’s for simulatio...

Mitch Bailey

08/08/2023, 2:03 PM

I created a set of schematics for the sky130

gpiov2

cell LVS. Feel free to post PR’s for simulation settings. LVS instructions are in the

README

file. Hopefully this will clarify some of the

verilog/rtl/user_defines.v

settings. https://github.com/d-m-bailey/sky130_fd_io.git

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Mitch Bailey

08/18/2023, 4:51 AM

@Tim Edwards looking at the

user_defines.v

gpio_control_block.v

, and the schematic, I’ve noticed

OUTPUT_DISABLE

has no effect in

USER

modes. Can you verify this? Here’s some relevant code from rtl.

Copy code

assign gpio_in_unbuf = pad_gpio_in;
    assign mgmt_gpio_in = (gpio_inenb == 1'b0 && gpio_outenb == 1'b1) ?
                        pad_gpio_in : 1'bz;
    assign pad_gpio_outenb = (mgmt_ena) ? ((mgmt_gpio_oeb == 1'b1) ?
                        gpio_outenb : 1'b0) : user_gpio_oeb;
    assign pad_gpio_out = (mgmt_ena) ? ((mgmt_gpio_oeb == 1'b1) ?
                        ((gpio_dm[2:1] == 2'b01) ? ~gpio_dm[0] : mgmt_gpio_out) :
                        mgmt_gpio_out) : user_gpio_out;

    /* Buffer user_gpio_in with an enable that is set by the user domain vccd */

    gpio_logic_high gpio_logic_high (
            .gpio_logic1(gpio_logic1)
    );

    sky130_fd_sc_hd__einvp_8 gpio_in_buf (
            .Z(user_gpio_in),
            .A(~gpio_in_unbuf),
            .TE(gpio_logic1)
    );

This means that

user_oeb

is always needed for

USER

modes (specifically,

INPUT

and

ANALOG

) to prevent Hi-Z input to the

pad_gpio_outenb

selector, correct? Also for

USER_INPUT_PULLDOWN

and

USER_INPUT_PULLUP

, it’s the designer’s responsibility to set

io_oeb

to low and

io_out

to high for pull up and low for pull down, right?

Tim Edwards

08/19/2023, 12:43 AM

@Mitch Bailey: Technically all true, but as we discussed, the

user_gpio_in

signal is always what's on the pad regardless of whether the mode is

MGMT

USER

, so input modes (other than pull-up and pull-down) can be made to work without

user_gpio_oeb

; and analog mode can always be made to work using

MGMT

mode and so also can work without

user_gpio_oeb

. The main issue is that for user output, the

user_gpio_oeb

line must be set low, and that is also true for the pull-up and pull-down input modes, for the reasons you mentioned.

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