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Updated Persistent Memory (markdown)

euquiq 2020-06-04 01:37:12 -03:00
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Persistent-Memory.md

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This is a small amount of ram (only 256 bytes), part of the **RTC (Real Time Clock) subsystem**, inside the LPC43xx chip on the portapack hardware.
# RTC Subsystem
The RTC subsystem also keeps the actual clock (date / time) running, powered by a CR2032 battery, (which needs to be installed on the portapack board!), even when the unit is not connected to an USB power source.
## backup_ram region
This persistent memory is part of the **RTC (Real Time Clock) subsystem**, inside the LPC43xx chip on the portapack hardware.
The **backup_ram region** is defined in `/firmware/common/memory_map.hpp` and labeled as "LPC_BACKUP_REG_BASE" starting at address **0x40041000**
If you are curious on how exactly these 256 bytes of persistent memory are arranged, it's defined on `/firmware/chibios-portapack/os/hal/platforms/LPC43xx/lpc43xx.inc`:
If you are curious on how exactly the whole persistent memory is arranged, it's defined on `/firmware/chibios-portapack/os/hal/platforms/LPC43xx/lpc43xx.inc`:
* **LPC_RTC_DOMAIN_BASE** (0x40040000)
* **LPC_ALARM_TIMER_BASE** (LPC_RTC_DOMAIN_BASE + 0x0000)
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* **LPC_OTP_CTRL_BASE** (LPC_RTC_DOMAIN_BASE + 0x5000)
* **LPC_RTC_BASE** (LPC_RTC_DOMAIN_BASE + 0x6000)
## backup_ram region
The **backup_ram region** is a small amount of ram (only 256 bytes), defined in `/firmware/common/memory_map.hpp` and labeled as "LPC_BACKUP_REG_BASE" starting at address **0x40041000**
### data_t struct
The Portapack firmware uses the backup_ram region to store several uint32_t (and one uint64_t) variables, inside a struct, called "data_t", declared on /firmware/common/portapack_persistent_memory.cpp