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The KEBA battery monitoring controller is found in the system FPGA of KEBA PLC devices. It puts a load on the coin cell battery to check the state of the battery. If the coin cell battery is nearly empty, then the user space is signaled with a hwmon alarm. The auxiliary device for this driver is instantiated by the cp500 misc driver. Signed-off-by: Gerhard Engleder <eg@keba.com> Link: https://lore.kernel.org/r/20250409190830.60489-1-gerhard@engleder-embedded.com Signed-off-by: Guenter Roeck <linux@roeck-us.net>
60 lines
2.6 KiB
ReStructuredText
60 lines
2.6 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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Kernel driver kbatt
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===================
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Supported chips:
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* KEBA battery monitoring controller (IP core in FPGA)
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Prefix: 'kbatt'
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Authors:
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Gerhard Engleder <eg@keba.com>
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Petar Bojanic <boja@keba.com>
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Description
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-----------
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The KEBA battery monitoring controller is an IP core for FPGAs, which
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monitors the health of a coin cell battery. The coin cell battery is
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typically used to supply the RTC during power off to keep the current
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time. E.g., the CP500 FPGA includes this IP core to monitor the coin cell
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battery of PLCs and the corresponding cp500 driver creates an auxiliary
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device for the kbatt driver.
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This driver provides information about the coin cell battery health to
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user space. Actually the user space shall be informed that the coin cell
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battery is nearly empty and needs to be replaced.
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The coin cell battery must be tested actively to get to know if its nearly
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empty or not. Therefore, a load is put on the coin cell battery and the
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resulting voltage is evaluated. This evaluation is done by some hard wired
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analog logic, which compares the voltage to a defined limit. If the
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voltage is above the limit, then the coin cell battery is assumed to be
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ok. If the voltage is below the limit, then the coin cell battery is
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nearly empty (or broken, removed, ...) and shall be replaced by a new one.
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The KEBA battery monitoring controller allows to start the test of the
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coin cell battery and to get the result if the voltage is above or below
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the limit. The actual voltage is not available. Only the information if
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the voltage is below a limit is available.
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The test load, which is put on the coin cell battery for the health check,
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is similar to the load during power off. Therefore, the lifetime of the
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coin cell battery is reduced directly by the duration of each test. To
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limit the negative impact to the lifetime the test is limited to at most
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once every 10 seconds. The test load is put on the coin cell battery for
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100ms. Thus, in worst case the coin cell battery lifetime is reduced by
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1% of the uptime or 3.65 days per year. As the coin cell battery lasts
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multiple years, this lifetime reduction negligible.
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This driver only provides a single alarm attribute, which is raised when
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the coin cell battery is nearly empty.
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====================== ==== ===================================================
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Attribute R/W Contents
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====================== ==== ===================================================
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in0_min_alarm R voltage of coin cell battery under load is below
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limit
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====================== ==== ===================================================
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