ARM: socfpga: enclustra-sa2: issue with I2C1

[David Picard]

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.

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

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
>