[core] Only enable D-Cache without :platform:dma module

src/modm/platform/core/cortex/module.lb

@@ -330,17 +330,25 @@ def validate(env):
 
 def build(env):
     env.substitutions = env.query("vector_table")
+    core = env.substitutions["core"]
+    with_icache = "m7" in core
+    with_dcache = with_icache and not (env.has_module(":platform:dma") or env.has_module(":platform:bdma"))
     env.substitutions.update({
         "target": env[":target"].identifier,
         "with_fault_storage": env.has_module(":platform:fault"),
         "with_memory_traits": env.has_module(":architecture:memory"),
         "with_assert": env.has_module(":architecture:assert"),
         "with_fpu": env.get("float-abi", "soft") != "soft",
         "with_multicore": env.has_module(":platform:multicore"),
-        "with_msplim": sum(c.isnumeric() for c in env.substitutions["core"]) == 2,
+        "with_msplim": sum(c.isnumeric() for c in core) == 2,
+        "with_icache": with_icache,
+        "with_dcache": with_dcache,
     })
     env.outbasepath = "modm/src/modm/platform/core"
 
+    if env.substitutions["with_icache"] and not env.substitutions["with_dcache"]:
+        env.log.warning("Cortex-M7 D-Cache is disabled due to using DMA!")
+
     # startup script
     env.template("reset_handler.sx.in")
     env.template("startup.c.in")

src/modm/platform/core/cortex/module.md

@@ -19,7 +19,7 @@ implemented as follows:
 3. Call `modm_initialize_platform()` to initialize the custom device hardware.
 4. Copy data to internal RAM.
 5. Zero sections in internal RAM.
-6. Initialize ARM Cortex-M core: enable FPU and relocate vector table.
+6. Initialize ARM Cortex-M core: enable FPU, caches and relocate vector table.
 7. Execute shared hardware initialization functions.
 8. Copy data to *external* RAM.
 9. Zero sections in *external* RAM.
@@ -62,11 +62,11 @@ perhaps even write this function in Assembly if deemed necessary.
 
 ### Cache Initialization
 
-For Cortex-M7 devices, both the I-Cache and D-Cache are enabled by default with
-a write-through policy to significantly improve performance. However, it is
-important to note that manual invalidation of the caches is required on certain
-operations, such as when writing to Flash (I-Cache) or when using DMA
-(D-Cache). See the [CMSIS-Core documentation][cache_api] for more info.
+For Cortex-M7 devices, the I-Cache is enabled by default. The D-Cache with a
+write-back write-allocate policy is only enabled if the `modm:platform:dma`
+module is NOT selected. modm currently does not support allocating DMA buffers
+in non-cachable regions or granular cache invalidation. See the
+[CMSIS-Core Cache API][cache_api] for more information on cache management.
 
 
 ### Additional Initialization

src/modm/platform/core/cortex/startup.c.in

@@ -24,6 +24,8 @@
 // ----------------------------------------------------------------------------
 // Default implementation of platform initialization
 modm_weak void modm_initialize_platform(void) {}
+extern void __modm_initialize_memory(void);
+extern int main(void);
 
 // ----------------------------------------------------------------------------
 // Linker section start and end pointers
@@ -96,26 +98,28 @@ void __modm_startup(void)
 	// Copy and zero all internal memory
 	table_copy(__table_copy_intern_start, __table_copy_intern_end);
 	table_zero(__table_zero_intern_start, __table_zero_intern_end);
-
-%% if "m7" in core
+%#
+%% if with_icache
 	// Enable instruction cache
 	SCB_InvalidateICache();
 	SCB_EnableICache();
-	// Enable data cache with write-through policy
+%% endif
+%% if with_dcache
+	// Enable data cache with default WBWA policy
 	SCB_InvalidateDCache();
 	SCB_EnableDCache();
 %% endif
-
+%#
 %% if core != "cortex-m0"
 	// Set the vector table location
 	SCB->VTOR = (uint32_t)__vector_table_{{ vector_table_location }}_start;
 %% endif
-
+%#
 %% if "m0" not in core
 	// Enable trapping of divide by zero for UDIV/SDIV instructions.
 	SCB->CCR |= SCB_CCR_DIV_0_TRP_Msk;
 %% endif
-
+%#
 	// Call all hardware initialize hooks
 	table_call(__hardware_init_start, __hardware_init_end);
 
@@ -124,16 +128,14 @@ void __modm_startup(void)
 	table_zero(__table_zero_extern_start, __table_zero_extern_end);
 
 	// Initialize heap as implemented by the heap option
-	extern void __modm_initialize_memory(void);
 	__modm_initialize_memory();
 
 	// Call all constructors of static objects
 	table_call(__init_array_start, __init_array_end);
 
 	// Call the application's entry point
-	extern int main(void);
 	main();
-
+%#
 %% if with_assert
 	// If main exits, assert here in debug mode
 	(void) modm_assert_continue_fail_debug(0,