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SMBUS for FELIX cards

Copied from an e-mail from Jos Vermeulen (20-11-2020, i2c in turano and brembo)

As Henk asked about SMBus support in general I had a look at brembo, our Epyc based server, to see whether the 712 in it is seen on SMBus. To do that I had first a look at turano to remind myself of how to do this, the answer is: first run i2cdetect -l to see which busses are there and then run i2cdetect x, with x the number of the bus to look at. For turano one sees this:

turano ~ 26 > i2cdetect -l
i2c-0 unknown AST i2c bit bus N/A
i2c-1 unknown SMBus I801 adapter at 0580 N/A

[root@turano i73]# i2cdetect 1
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-1.
I will probe address range 0x03-0x77.
Continue? [Y/n] Y
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- 08 -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 1f
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- 44 -- -- -- 48 -- -- -- -- -- -- --
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- 61 -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- 77

In the range 0x70 to 0x77 we should see two addresses as there are two 712s installed. However, only the default address of 0x77 is seen, so both cards have the same i2c address. This has to be changed, by changing the jumper settings on one of the cards.

i2cdetect -l shows this on brembo

brembo ~ 26 > i2cdetect -l
i2c-0 unknown AST i2c bit bus N/A
i2c-1 unknown SMBus PIIX4 adapter port 0 at 0b00 N/A
i2c-2 unknown SMBus PIIX4 adapter port 2 at 0b00 N/A
i2c-3 unknown SMBus PIIX4 adapter port 3 at 0b00 N/A
i2c-4 unknown SMBus PIIX4 adapter port 4 at 0b00 N/A

So there are 4 busses, but there is no device on any of the busses. Inspection of the manual revealed that there are 4 SMBus headers to which devices can be connected, these probably are associated with the 4 busses. However, usage of the SMBus as is possible in the standard FELIX servers or Gen III ROS PCs does not seem to be possible. The manual of the motherboard in brembo can be found here:

https://www.asrockrack.com/general/productdetail.asp?Model=ROMED8-2T#Specifications

I had also a look at motherboards for the Epyc CPU from Supermicro, to see whether these support the use of SMBus as we need it for the 712 for using fflash. These boards have the same problem as the ASRock board in brembo. Nevertheless one of the boards, the H12SSL-i, may be of interest for lab usage. It has 5 16 lane Gen4 slots that support 2 x 8 bifurcation, see:

https://www.supermicro.com/en/products/motherboard/H12SSL-i

Rene: I think it would make sense to ask TWP (www.twp.nl) for a quotation, see my next message.

Given the problems with SMBus usage I think that we need to think about an alternative for Phase-II systems. One possibility is a USB - i2c interface that connects to an i2c connector on the FELIX FPGA card. We have tried this in the past. Another alternative could be to make use of a small USB JTAG dongle for each card. Direct communication via USB with an on-board microcontroller could be another alternative.

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