ARM: socfpga: enclustra-sa2: issue with I2C1

[Steffen Trumtrar]

On 2026-04-27 at 12:09 +02, David Picard <david.picard at clermont.in2p3.fr> wrote:

Hi,

> Hi Stephen, thanks for your reply,
> 
> Pins SDA and SCL, GPIO51 and GPIO52 respectively, are specified with the I/O
> standard 3.3V LVCMOS and a drive strength of 2mA, which is way more than needed,
> given my 10K pull-up resistors (3.3 / 10K = 0.33mA). I know that 10K is bigger
> than the usual 2.2K, but probably not big enough to prevent any change on the
> SCL line. I just see a perfect flat line when I probe the bus.
>

:(

> I compared iocsr_config_cyclone5.c and pinmux_config.c in the terasic-de10-nano/
> and enclustra-sa2/ directories. There are a lot of differences. But the lines
> that changed in enclustra-sa2/ when I tried to enable the I2C1 bus are now the
> same as in the terasic-de10-nano/ directory, which probably makes sense.
>

Makes sence, yes and was what I hoped for. But, doesn't seem to change anything.

> Does Barebox have to decipher every bit in those cryptic files?
>

barebox knows nothing about the meaning of the iocsr registers. Those values a just written to the hardware and can't be changed afterwards.
AFAIK there still is no linux driver that might read and decipher the settings.

Sadly, I don't have any more ideas at the top of my head why it doesn't work. Everything sounds correct.


Best regards,
Steffen

> 
> David
> 
> 
> Le 24/04/2026 à 09:27, Steffen Trumtrar a écrit :
> > On 2026-04-23 at 14:00 +02, David Picard <david.picard at clermont.in2p3.fr>
> > wrote:
> >
> > Hi,
> >
> >> Hello,
> >>
> >> @Stephen and Ian: I Cc you since I spotted you authored commits related to
> >> Intel
> >> SoC FPGA pin muxing.
> >>
> >
> > long time ago ;)
> >
> >> I'm trying to enable the I2C1 bus on a Cyclone V-base module, mounted on a
> >> base
> >> board. The I2C1 lines connect to a 2.54mm header, on which I attached a I²C
> >> device with pull-up resistors at address 0x40.
> >> https://www.enclustra.com/en/products/system-on-chip-modules/mercury-sa2/ I
> >> can't detect the I²C device, nor can I see any pulse on the SCL line, which
> >> is
> >> constantly at +3.3V.
> >>
> >> I changed the pin muxing in Quartus, updated the handoff files, changed the
> >> devicetree. The I2C1 bus is visible in Barebox and Linux. More detail here:
> >> https://community.altera.com/discussions/fpga-device/cyclone-v-hps-i2c1-issue-no-activity-on-bus/352583 
> >
> > I remember, that iocsr was 'underdocumented' to say the least...
> >
> > Wasn't it possible to change drive strength and those settings or was that
> > with Xilinx/Zynq?
> >
> >> As documented on the Barebox website, I generated the BSP files with the
> >> Quartus
> >> script bsp-create-settings and copied the handoff files to the Barebox build
> >> directory. After that, I could see that iocsr_config_cyclone5.c and
> >> pinmux_config.c had changed.
> >> https://www.barebox.org/doc/2025.05.0/boards/socfpga.html#updating-handoff-files
> >> https://www.intel.com/content/www/us/en/docs/programmable/683187/20-1/bsp-create-settings.html
> >> If someone could give me some hint, that would be really great!
> >
> > I see, that the Terasic DE10 Nano uses i2c1. Maybe compare the changed iocsr
> > with those?
> >
> >
> > Best regards,
> > Steffen
> >

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