DMFMC - DMOD FMC (Flexible Memory Controller) Driver Module

A dmod driver module for the STM32 FMC peripheral, providing access to external memory (currently SDRAM) wired to the microcontroller. Loaded automatically by dmdevfs, the same way dmuart and dmgpio are.

Features

• SDRAM configuration (column/row/bank geometry, CAS latency, all JEDEC timing parameters, auto-refresh) derived entirely from a chip descriptor - no manual register math required to support a new SDRAM chip.
• Automatic SDCLK frequency selection (HCLK/2 or HCLK/3, whichever is the fastest the chip tolerates).
• Optional registration of the mapped memory as an additional dmheap context, so application code can dmheap_malloc() straight into external RAM.
• Optional SDRAM refresh-error interrupt reporting through dmhaman.
• Split into dmfmc (MCU-agnostic) and dmfmc_port (MCU-family specific), like every other dmod hardware driver.
• NOR/NAND Flash and PSRAM are declared in the port contract for future support, but not yet implemented (only SDRAM is).

Quick Start

Installation

# Create a dependencies file (deps.dmd)
echo "dmfmc board/stm32f746g-disco/sdram.ini" >> deps.dmd

# Install with configuration
dmf-get deps.dmd

Basic Usage

#include "dmfmc.h"
#include "dmdrvi.h"
#include "dmini.h"

dmini_context_t config = dmini_load("sdram.ini");
dmdrvi_dev_num_t dev_num = {0};

dmdrvi_context_t fmc_ctx = dmfmc_dmdrvi_create(config, &dev_num);
void *handle = dmfmc_dmdrvi_open(fmc_ctx, DMDRVI_O_RDWR);

uint8_t buffer[256];
dmfmc_dmdrvi_write(fmc_ctx, handle, buffer, sizeof(buffer), 0);
dmfmc_dmdrvi_read(fmc_ctx, handle, buffer, sizeof(buffer), 0);

void *sdram_start = NULL;
dmfmc_dmdrvi_ioctl(fmc_ctx, handle, dmfmc_ioctl_cmd_get_memory_start, &sdram_start);

dmfmc_dmdrvi_close(fmc_ctx, handle);
dmfmc_dmdrvi_free(fmc_ctx);

Most applications never call this API directly - dmdevfs creates the context automatically from configs/board/*/sdram.ini at boot, and the memory is either used directly (/dev/sdram, or the alt-name from the INI section) or transparently through dmheap_malloc() when heap_usage=heap is set.

Building

Prerequisites

• CMake 3.18+
• GCC-compatible cross compiler for the target MCU

Build Commands

# Configure for STM32F7
cmake -DDMFMC_MCU_SERIES=stm32f7 -DDMOD_MODE=DMOD_MODULE -B build -S .

# Build
cmake --build build/

Documentation

See docs/ for the architecture overview, API reference, configuration reference, and a guide for adding a new MCU port.

Supported Platforms

MCU Series	Status	Notes
STM32F7	Implemented	Targets STM32F746G-Discovery (MT48LC4M32B2 SDRAM); under active hardware bring-up, see configs/board/stm32f746g-disco/sdram.ini for the board-specific 16-bit bus note.
STM32F4	Implemented	Targets F42x/43x/469/479 (the F4 parts with an FMC, not just an FSMC). Not yet validated on real hardware.

Supported Memory Chips

Chip	Type	Capacity	Boards
Micron MT48LC4M32B2	SDRAM	128 Mbit (4M x 32)	STM32F746G-Discovery

Configuration Examples

See configs/README.md for the full INI key reference and board configuration examples.

Development

Project Structure

dmfmc/
├── include/               # Public headers (dmfmc.h, dmfmc_port.h, dmfmc_types.h, dmfmc_chips.h)
│   └── port/              # Register definitions (stm32_common_regs.h, stm32f4_regs.h, stm32f7_regs.h)
├── src/
│   ├── dmfmc.c            # Common driver: dmdrvi contract, configuration, dmheap integration
│   ├── dmfmc_chips.c      # Known-chip database and JEDEC bring-up sequences
│   └── port/
│       ├── stm32_common/  # SDRAM controller logic shared by STM32F4 and STM32F7
│       ├── stm32f4/       # Lifecycle + IRQ registration for STM32F4
│       └── stm32f7/       # Lifecycle + IRQ registration for STM32F7
├── configs/               # Board configuration files (pins + FMC settings)
├── docs/                  # Architecture, API and configuration documentation
├── examples/              # Minimal standalone INI example
└── tests/                 # Host-buildable unit tests (chip database, no hardware required)

Adding New Platform Support

See docs/port-implementation.md.

Adding a New Memory Chip

See docs/configuration.md. In short: add a dmfmc_chip_info_t entry to src/dmfmc_chips.c with the chip's datasheet timing parameters and a JEDEC bring-up function, dispatched by a new dmfmc_chip_id_t enum value rather than a stored function pointer (dmod modules don't support relocating pointers embedded in static data - see docs/api-reference.md). No port-layer changes are required - dmfmc_port derives every register value from the chip descriptor at configuration time.

License

See LICENSE.

Related Projects

• dmod - the module loading framework this driver plugs into
• dmuart, dmgpio - sibling drivers using the same common/port split
• dmheap - heap manager this driver can register external RAM with