1  # coreboot Console
 2  
 3  coreboot supports multiple ways to access its console.
 4  <https://www.coreboot.org/Console_and_outputs>
 5  
 6  
 7  ## SMBus Console
 8  
 9  SMBus is a two-wire interface which is based on the principles of
10  operation of I2C. SMBus, was first was designed to allow a battery to
11  communicate with the charger, the system host, and/or other
12  power-related components in the system.
13  
14  Enable 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
17  slave I2C device which you will use to capture I2C packets.
18  
19  Modern computer Random Access Memory (RAM) slot has SMBus in it
20  according to the JEDEC standards. We can use a breakout-board to expose
21  those SMBus pins. Some mainboard have SMBus pins in the PCIe slot as
22  well.
23  
24  This 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  
33  A minimal DDR3 DIMM breakout board PCB design with only the
34  SDA(Data line) and SCL(Clock line) pins of I2C/SMBus can be found
35  [here](https://github.com/drac98/ram-breakout-board).
36  See the PCB layout [here](https://archive.org/details/ddr3-dimm-F_Cu)
37  
38  NOTE:
39  To capture the I2C packets, an I2C slave device is required. The easiest
40  way to capture the log message is to use a I2C to UART converter chip
41  with 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  
51  Watch this [video](https://youtu.be/Q0dK41n9db8) to see how it is set
52  up. A backup of the video is available
53  [here](https://web.archive.org/web/20220916172605/https://www.youtube.com/watch?v=Q0dK41n9db8)
54  
55  If you are using any of the `SC16IS740/750/760` I2C to UART converter
56  chip, you can enable the `SC16IS7XX_INIT` option to initialize the chip.
57  
58  If not we can use other I2C slave devices like an Arduino or a
59  Beagleboard.
60  * [Linux I2C Slave interface](https://web.archive.org/web/20220926173943/https://www.kernel.org/doc/html/latest/i2c/slave-interface.html)
61  * [BeagleBone 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)
62  
63  This feature was added as part of a GSoC 2022 project. Checkout the
64  following blog posts for more details.
65  * [coreboot Console via SMBus — Part I](https://medium.com/@husnifaiz/coreboot-console-via-smbus-introduction-38273691a8ac)
66  * [coreboot Console via SMBus — Part II](https://medium.com/@husnifaiz/coreboot-console-via-smbus-part-ii-bc324fdd2f24)