hi @Mitch Bailey when we are using the io pins in caravel user area, we can find out,in and oenb. in firmware we can define io pins to be input or output so that means either input or output pins will be mux. but if we use io_oenb, how does the logic overright firmware? oenb is userarea logic. I am not sure about io input /output muxing logic in user area, and how is it decoupled from managementment control of these pins

@samarth jain I think what you are asking about is how to configure the gpio cells. This is done with the

caravel_user_project/verilog/rtl/user_defines.v

file that you must modify. See the

GPIO Configuration

section here. gpio’s that are configured for output or as bidirectional require the corresponding

io_oenb

to be low when output is enabled. It is probably a good idea to tie unused

io_out

and

io_oenb

signals to power or ground to avoid possible leakage due to unconnected gate input.

@Mitch Bailey so if my user area needs a io to be output, I can connect the wire from user area net to Io_out and connect io_oenb to gnd in the gds? other case if I need the io to be input, I can connect the net from userarea to io_in and also connect the io_oenb to vcc of user area ?

@samarth jain good questions! There was a bit of confusion on this subject which resulted in the creation of an oeb check program as part of

mpw_precheck

. Here are the 13 predefined gpio configurations

GPIO_MODE_MGMT_STD_INPUT_NOPULL
GPIO_MODE_MGMT_STD_INPUT_PULLDOWN
GPIO_MODE_MGMT_STD_INPUT_PULLUP
GPIO_MODE_MGMT_STD_OUTPUT
GPIO_MODE_MGMT_STD_BIDIRECTIONAL
GPIO_MODE_MGMT_STD_ANALOG

GPIO_MODE_USER_STD_INPUT_NOPULL
GPIO_MODE_USER_STD_INPUT_PULLDOWN
GPIO_MODE_USER_STD_INPUT_PULLUP
GPIO_MODE_USER_STD_OUTPUT
GPIO_MODE_USER_STD_BIDIRECTIONAL
GPIO_MODE_USER_STD_OUT_MONITORED
GPIO_MODE_USER_STD_ANALOG

In order to propagate an external input signal to the user area, the gpio should be programmed as one of the following.

GPIO_MODE_MGMT_STD_INPUT_NOPULL
GPIO_MODE_MGMT_STD_INPUT_PULLDOWN
GPIO_MODE_MGMT_STD_INPUT_PULLUP
GPIO_MODE_MGMT_STD_BIDIRECTIONAL

GPIO_MODE_USER_STD_INPUT_NOPULL
GPIO_MODE_USER_STD_INPUT_PULLDOWN
GPIO_MODE_USER_STD_INPUT_PULLUP
GPIO_MODE_USER_STD_BIDIRECTIONAL
GPIO_MODE_USER_STD_OUT_MONITORED

Note that all

MGMT

input is also input to the user area. For

GPIO_MODE_USER_STD_INPUT_PULLDOWN
GPIO_MODE_USER_STD_INPUT_PULLUP

The

USER

must provide the appropriate output on

io_out

(fixed low for pull down and fixed high for pull up) AND set

io_oeb

to low. In order to have the user output actually output from the gpio cell,

io_oeb

should be low and one of the following modes should be used.

GPIO_MODE_USER_STD_OUTPUT
GPIO_MODE_USER_STD_BIDIRECTIONAL
GPIO_MODE_USER_STD_OUT_MONITORED

In these modes,

io_oeb

high will disable the gpio output buffer (Hi-Z output), which will allow external input in the case of

GPIO_MODE_USER_STD_BIDIRECTIONAL
GPIO_MODE_USER_STD_OUT_MONITORED

In these 2 modes, when

io_oeb

is low, the user input

io_in

will follow

io_out

. In summary…. For simple input usage, Set the gpio mode to

GPIO_MODE_USER_STD_INPUT_NOPULL

and tie

io_out

and

io_oeb

high or low to Hi-Z avoid leakage. For simple always enabled output usage, Set the gpio mode to

GPIO_MODE_USER_STD_OUTPUT

and tie

io_oeb

low.