67 lines
2.9 KiB
Markdown
67 lines
2.9 KiB
Markdown
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# coreboot Console
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coreboot supports multiple ways to access its console.
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https://www.coreboot.org/Console_and_outputs
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## SMBus Console
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SMBus is a two-wire interface which is based on the principles of
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operation of I2C. SMBus, was first was designed to allow a battery to
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communicate with the charger, the system host, and/or other
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power-related components in the system.
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Enable the SMBus console with `CONSOLE_I2C_SMBUS` Kconfig. Set
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`CONSOLE_I2C_SMBUS_SLAVE_ADDRESS` and
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`CONSOLE_I2C_SMBUS_SLAVE_DATA_REGISTER` configuration values of the
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slave I2C device which you will use to capture I2C packets.
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Modern computer Random Access Memory (RAM) slot has SMBus in it
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according to the JEDEC standards. We can use a breakout-board to expose
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those SMBus pins. Some mainboard have SMBus pins in the PCIe slot as
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well.
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This feature has been tested on the following platforms:
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```eval_rst
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+------------------------------------+
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| Tested platforms |
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+====================================+
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| GA-H61M-S2PV + Intel Ivy Bridge |
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+---------------------+---------------
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```
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A minimal DDR3 DIMM breakout board PCB design with only the
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SDA(Data line) and SCL(Clock line) pins of I2C/SMBus can be found
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[here](https://github.com/drac98/ram-breakout-board).
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See the PCB layout [here](https://archive.org/details/ddr3-dimm-F_Cu)
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NOTE:
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To capture the I2C packets, an I2C slave device is required. The easiest
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way to capture the log message is to use a I2C to UART converter chip
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with a UART to USB converter chip. The setup would be as follows.
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```text
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+---------+ +-------------+ +-------------+
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+ PC +----+ UART to USB +----+ I2C to UART |
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+---------+ +-------------+ +-------------+
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------------------------------------------------+-- System Management
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----------------------------------------------+---- Bus
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```
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Watch this [video](https://youtu.be/Q0dK41n9db8) to see how it is set
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up. A backup of the video is available
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[here](https://web.archive.org/web/20220916172605/https://www.youtube.com/watch?v=Q0dK41n9db8)
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If you are using any of the `SC16IS740/750/760` I2C to UART converter
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chip, you can enable the `SC16IS7XX_INIT` option to initialize the chip.
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If not we can use other I2C slave devices like an Arduino or a
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Beagleboard.
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* [Linux I2C Slave interface](https://web.archive.org/web/20220926173943/https://www.kernel.org/doc/html/latest/i2c/slave-interface.html)
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* [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)
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This feature was added as part of a GSoC 2022 project. Checkout the
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following blog posts for more details.
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* [coreboot Console via SMBus — Part I](https://medium.com/@husnifaiz/coreboot-console-via-smbus-introduction-38273691a8ac)
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* [coreboot Console via SMBus — Part II](https://medium.com/@husnifaiz/coreboot-console-via-smbus-part-ii-bc324fdd2f24)
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