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1# coreboot Console
2
3coreboot supports multiple ways to access its console.
4https://www.coreboot.org/Console_and_outputs
5
6
7## SMBus Console
8
9SMBus is a two-wire interface which is based on the principles of
10operation of I2C. SMBus, was first was designed to allow a battery to
11communicate with the charger, the system host, and/or other
12power-related components in the system.
13
14Enable the SMBus console with `CONSOLE_I2C_SMBUS` Kconfig. Set
15`CONSOLE_I2C_SMBUS_SLAVE_ADDRESS` and
16`CONSOLE_I2C_SMBUS_SLAVE_DATA_REGISTER` configuration values of the
17slave I2C device which you will use to capture I2C packets.
18
19Modern computer Random Access Memory (RAM) slot has SMBus in it
20according to the JEDEC standards. We can use a breakout-board to expose
21those SMBus pins. Some mainboard have SMBus pins in the PCIe slot as
22well.
23
24This feature has been tested on the following platforms:
25```{eval-rst}
26+------------------------------------+
27| Tested platforms                   |
28+====================================+
29| GA-H61M-S2PV + Intel Ivy Bridge    |
30+------------------------------------+
31```
32
33A minimal DDR3 DIMM breakout board PCB design with only the
34SDA(Data line) and SCL(Clock line) pins of I2C/SMBus can be found
35[here](https://github.com/drac98/ram-breakout-board).
36See the PCB layout [here](https://archive.org/details/ddr3-dimm-F_Cu)
37
38NOTE:
39To capture the I2C packets, an I2C slave device is required. The easiest
40way to capture the log message is to use a I2C to UART converter chip
41with a UART to USB converter chip. The setup would be as follows.
42```text
43+---------+    +-------------+    +-------------+
44+   PC    +----+ UART to USB +----+ I2C to UART |
45+---------+    +-------------+    +-------------+
46                                              | |
47------------------------------------------------+--  System Management
48----------------------------------------------+----  Bus
49```
50
51Watch this [video](https://youtu.be/Q0dK41n9db8) to see how it is set
52up. A backup of the video is available
53[here](https://web.archive.org/web/20220916172605/https://www.youtube.com/watch?v=Q0dK41n9db8)
54
55If you are using any of the `SC16IS740/750/760` I2C to UART converter
56chip, you can enable the `SC16IS7XX_INIT` option to initialize the chip.
57
58If not we can use other I2C slave devices like an Arduino or a
59Beagleboard.
60```{toctree}
61:maxdepth: 1
62
63Linux I2C Slave interface <https://web.archive.org/web/20220926173943/https://www.kernel.org/doc/html/latest/i2c/slave-interface.html>
64BeagleBone Black I2C Slave <https://web.archive.org/web/20220926171211/https://forum.beagleboard.org/t/beaglebone-black-and-arduino-uno-i2c-communication-using-c/29990/8>
65```
66
67This feature was added as part of a GSoC 2022 project. Checkout the
68following blog posts for more details.
69```{toctree}
70:maxdepth: 1
71
72coreboot Console via SMBus — Part I <https://medium.com/@husnifaiz/coreboot-console-via-smbus-introduction-38273691a8ac>
73coreboot Console via SMBus — Part II <https://medium.com/@husnifaiz/coreboot-console-via-smbus-part-ii-bc324fdd2f24>
74```
75