Hi, can anyone please tell me the the difference between GPIO_MODE_USER_STD_ANALOG and GPIO_MODE_MGMT_STD_ANALOG? I know that the MGMT_ENABLE pin is high for the later one. But what difference does it make regrading input, output buffers and leakage?

In both, the

GPIO_MODE_USER_STD_ANALOG

and

GPIO_MODE_MGMT_STD_ANALOG

mode both the input and output buffers are disabled. If you have unconnected

io_out

or

io_oeb

signals, there may be Hi-Z leakage with

GPIO_MODE_USER_STD_ANALOG

. The

analog_io

connection is the same for either one, so I recommend using

GPIO_MODE_MGMT_STD_ANALOG.

Mitch Bailey, thank you so much for answer. Where should I connect io_out and io_oeb pins if I am not using GPIO pins for GPIO_MODE_USER_STD_ANALOG.

It's never a bad idea just to tie off

io_oeb

to digital (1.8V) power and

io_out

to either digital power or ground, just to be pedantic, but if you have analog connections and intend to keep the GPIO in

GPIO_MODE_MGMT_STD_ANALOG

mode, then they can be left open.

Ok. Thank you so much for the answer. I have couple of questions : I am designing an analog circuit. Can I use vccd for an external biasing voltage of 0.9V?

How much current is being drawn on the bias? I would think that the bias would be appropriate for the analog pin on a GPIO as long as you can tolerate the series resistor. The analog GPIO connection is not appropriate at all for a power supply. Why can't you use the

vdda1

or

vdda2

supplies, which are designed for that?

Ok. The bias voltage is to the gate so the current drawn is negligible. I saw the example user_analog_project and I think VDD was connected to the io_analog[4] pin there. So I thought it was fine but I will change it.

There are two different ways to connect analog. On the "caravan" chip (caravel_user_project_analog), you have the

io_analog

connections which are straight out to pads with no other connections, and

gpio_analog

on the GPIO (with series resistor) and

gpio_nosed

(without a series resistor). On the "caravel" chips (caravel_user_project), you have the

analog_io

connections on GPIO pins which have the series resistor (and which really ought to have been named

gpio_analog

to match the pins of the same function on caravan; I guess I am the one to blame for that confusing nomenclature).

Ok. Sorry for the confusion. I am talking about caravel_user_project_analog.

Okay, sorry, you are working in the caravan chip design, and yes,

io_analog[4]

with the ESD clamp circuit should be perfect for a 5V supply.

Ok. :)

The configuration for each GPIO is a set of 13 bits. It exists in two places: Inside the SoC (housekeeping), and next to each GPIO. The values in housekeeping are accessible through the memory map and so they can be defined in C code and then loaded into the locations next to each GPIO. That's the normal way to configure the GPIOs, because it's software-definable. However, there are cases in which a user may want the GPIO pins to be operational for the user project immediately on power-up, or they may want the user project to run without the SoC running at all, in which case the state of the GPIOs on power-up is critical. The "user_defines.v" specifies the default state of the configuration locally at the GPIO itself. It is implemented as a small via-programmed ROM close to the GPIO. The via programming is done by python script from the Makefile.

Ok. I think I got it. I will keep all the GPIO pins in GPIO_MODE_MGMT_STD_ANALOG in user_defines.v.

The GPIO are good for analog voltages up to the value of VDDIO, which is nominally 3.3V.

Not for 5V?

@Tim Edwards, can we overwrite the settings in user_defines.v, or if we messed it up we need to reprogram it each time? It's a ROM from what you mention, so I assume we can reprogram it, but just to be sure.

@Jorge Marin: I sense some confusion here. If you got the defaults wrong in "user_defines.v" you can still reconfigure the GPIO at any time from a program.

@Tim Edwards but I would like to make a setup that is not dependent on too many peripheric systems, ideally not needing to reprogram each time

@Jorge Marin: Then you just need to make sure that you have the correct

user_defines.v

contents.

@Tim Edwards that's the point, we misunderstood the settings and would like to change user_defines.v. Is this hardwired, or we can change it once and forever (unless we need to change smth else)?

@Jorge Marin The

user_defines.v

are translated into hard wired defaults during the tapeout process. These defaults may be programmatically overridden, but it needs to be done each time you power up the device. If you want to change the start up defaults, you’ll need to change the

user_defines.v

settings and resubmit your precheck/tapeout.