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configs: bring up SDRAM early with negative driver_order #3

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Merged
JohnAmadis merged 1 commit into from
Oct 1, 2026
Merged

configs: bring up SDRAM early with negative driver_order #3

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12 changes: 7 additions & 5 deletions configs/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -21,17 +21,19 @@ config would not be meaningful. Configs live only under `board/`.

Each config file contains:
- One `[sdram_*]` GPIO section per FMC signal pin (`driver_name=dmgpio`,
alternate function mode), with `driver_order=1` so they configure first.
- One driver section with `driver_name=dmfmc` and `driver_order=2`, so
alternate function mode), with `driver_order=-9` so they configure first.
- One driver section with `driver_name=dmfmc` and `driver_order=-8`, so
`dmdevfs` configures every pin before bringing up the FMC controller
itself - the same convention `dmuart` uses for its TX/RX pins.
itself - the same convention `dmuart` uses for its TX/RX pins. Both orders
are negative so the SDRAM heap is up right after `dmclk` (`driver_order=-10`)
and before any driver with the default order 0 starts allocating from DTCM.

### Example (stm32f746g-disco/sdram.ini, abridged)

```ini
[sdram_sdclk]
driver_name=dmgpio
driver_order=1
driver_order=-9
pin=PG8
mode=alternate
alternate_function=12
Expand All @@ -44,7 +46,7 @@ output_circuit=push_pull

[sdram]
driver_name=dmfmc
driver_order=2
driver_order=-8
memory_type=sdram
chip=MT48LC4M32B2
bank=1
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