Lightweight partitioned BaseFlash registry

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Lightweight partitioned BaseFlash registry

Postby faisal » Mon Oct 31, 2022 6:06 pm

This is a lightweight layer to register BaseFlash devices along with partitions for the application layer. This allows the application to address/access a particular partition of a particular device with path like "sda1/config". This is useful, and probably all most embedded applications need - as opposed to a full filesystem with directory hierarchy and so forth. It fills a niche between raw flash access, and something like FatFS or LittleFs. It's different than MFS - which is feature rich but confines you to use it in a certain way.

You can define a device with various partitions like this:

Code: Select all

static struct smtd_partition snorparts[] = {
    .name = "config"
    .offset = 0,
    .size = 1024,
    .name = "histograms"
    .offset = 1024,
    .size = 1024,
    .name = "diags"
    .offset = 2048,
    .size = 1024,

static struct smtd_info snor1 = {
    .name = "sda",
    .drv = (BaseFlash *)&SNORDriver,
    .erase_range = NULL,
    .partitions = &snorparts,
    .npart = sizeof(snorparts)/sizeof(snorparts[0]),

And you can have multiple devices with partitions - just define another struct smtd_info for each.

Register the struct smtd_info with the system like so:

Code: Select all

etc ...

The application can get a context (or call it a handle) to a specific partition by just giving a path "<device>/<partition>".
The context stores a current file position as well. So you can use typical read/write/fseek/ftell like APIs. The offsets/position/sector_index of the partition are relative to the start of the partition. That's really the bulk of what this layer is doing - constraining and address translation between the partition base address and the actual memory location in the device itself.

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smtd_ctx_t * fp = smtd_get_ctx("sda/histograms");

flash_offset_t cur_pos = smtd_ftell(fp);

smtd_fseek(fp, cur_pos + 100, SMTD_SEEK_CUR);

smtd_write(fp, buf, sizeof(buf));

If anyone's gonna use this - it needs to be updated to use the acquire_exclusive/release_exclusive BaseFlash APIs (it's just a few lines). When I get around to it, I'll update this post.
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