The overall goal and then the specifics of what's been tried: I'm trying to utilize as much of the left-over flash space as possible to store environmental data during periods of non-connectivity with a Bluetooth hub. I'm running into issues of incomplete writes and occasional faults that appear to be due to timing issues while performing write and erase operations.
Scenario: I'm working on an nRF51 device with 256kB of flash space. The SDK 12.3 is in use with v2.0.1 of the S130 SoftDevice. The device acts as a peripheral and there is only one master connection at a time. The connection is maintained for long durations while the master device is in range and the connection is dropped when page erase operations have to be performed. I'm using around 100 pages right now to store unaligned samples across words but staying within pages. The last four pages are left unused although I believe only one is needed by the peer manager for bonding information. I'm also leaving two pages of buffer space from the end of the application, but for no particular reason at the moment. Calls to write and erase can happen asynchronously as they are kicked off by both internally timed events and Bluetooth events caused by hub interactions.
What's in use right now: I'm currently using the S130 functions, sd_flash_write() and sd_flash_page_erase(). I was originally using the NVMC functions from the peripheral drivers, namely nrf_nvmc_page_erase and nrf_nvmc_write_bytes(), etc. I had to stop using the NVMC functions because of timing issues during both Bluetooth connections and while advertising. The writes would work 99% of the time as far as I could tell but the erases failed every time because of the 20ms halts being caused by the flash operation. The sd_flash_write and sd_flash_erase operations work some of the time. They always return NRF_SUCCESS but do not always seem to complete their operations. I tried using the event getter, sd_evt_get(), but this doesn't seem to generate any events. I didn't see any requirement to register an event handler and the call is used to poll for an event, not respond to a callback, at least as far as the documentation states.
With the requirement to use as much of the left-over space as possible, it looks like the FDS is not an option. But maybe it is and I'm misunderstanding how the space allocation works. fstorage might be an option but it's not clear if I can control the page allocation enough to get as much space as I'd like. I haven't tried the flash manager either. Are the SoftDevice functions the right place to be handling the flash read and write operations? Or is the FDS, flash manager, or fstorage the safer and more correct way to access the flash while still doing bluetooth operations?
