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diff --git a/Documentation/technotes/console.md b/Documentation/technotes/console.md new file mode 100644 index 0000000000..8cc5b38fc9 --- /dev/null +++ b/Documentation/technotes/console.md @@ -0,0 +1,66 @@ +# coreboot Console + +coreboot supports multiple ways to access its console. +https://www.coreboot.org/Console_and_outputs + + +## SMBus Console + +SMBus is a two-wire interface which is based on the principles of +operation of I2C. SMBus, was first was designed to allow a battery to +communicate with the charger, the system host, and/or other +power-related components in the system. + +Enable the SMBus console with `CONSOLE_I2C_SMBUS` Kconfig. Set +`CONSOLE_I2C_SMBUS_SLAVE_ADDRESS` and +`CONSOLE_I2C_SMBUS_SLAVE_DATA_REGISTER` configuration values of the +slave I2C device which you will use to capture I2C packets. + +Modern computer Random Access Memory (RAM) slot has SMBus in it +according to the JEDEC standards. We can use a breakout-board to expose +those SMBus pins. Some mainboard have SMBus pins in the PCIe slot as +well. + +This feature has been tested on the following platforms: +```eval_rst ++------------------------------------+ +| Tested platforms | ++====================================+ +| GA-H61M-S2PV + Intel Ivy Bridge | ++---------------------+--------------- +``` + +A minimal DDR3 DIMM breakout board PCB design with only the +SDA(Data line) and SCL(Clock line) pins of I2C/SMBus can be found +[here](https://github.com/drac98/ram-breakout-board). +See the PCB layout [here](https://archive.org/details/ddr3-dimm-F_Cu) + +NOTE: +To capture the I2C packets, an I2C slave device is required. The easiest +way to capture the log message is to use a I2C to UART converter chip +with a UART to USB converter chip. The setup would be as follows. +```text ++---------+ +-------------+ +-------------+ ++ PC +----+ UART to USB +----+ I2C to UART | ++---------+ +-------------+ +-------------+ + | | +------------------------------------------------+-- System Management +----------------------------------------------+---- Bus +``` + +Watch this [video](https://youtu.be/Q0dK41n9db8) to see how it is set +up. A backup of the video is available +[here](https://web.archive.org/web/20220916172605/https://www.youtube.com/watch?v=Q0dK41n9db8) + +If you are using any of the `SC16IS740/750/760` I2C to UART converter +chip, you can enable the `SC16IS7XX_INIT` option to initialize the chip. + +If not we can use other I2C slave devices like an Arduino or a +Beagleboard. +* [Linux I2C Slave interface](https://web.archive.org/web/20220926173943/https://www.kernel.org/doc/html/latest/i2c/slave-interface.html) +* [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) + +This feature was added as part of a GSoC 2022 project. Checkout the +following blog posts for more details. +* [coreboot Console via SMBus — Part I](https://medium.com/@husnifaiz/coreboot-console-via-smbus-introduction-38273691a8ac) +* [coreboot Console via SMBus — Part II](https://medium.com/@husnifaiz/coreboot-console-via-smbus-part-ii-bc324fdd2f24) diff --git a/Documentation/technotes/index.md b/Documentation/technotes/index.md index fda8bd6219..da5b8644d2 100644 --- a/Documentation/technotes/index.md +++ b/Documentation/technotes/index.md @@ -5,3 +5,4 @@ * [Unit testing coreboot](2020-03-unit-testing-coreboot.md) * [Unit Test Code Coverage](2021-05-code-coverage.md) * [Address Sanitizer](asan.md) +* [coreboot Consoles](console.md) |