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