pbio/include/pbdrv/compiler.h: Move intrinsics into header

Currently contains a compiler memory barrier and fall-through marker.
These operations will be needed throughout the driver layer.

Author: ArcaneNibble

lib/pbio/drv/block_device/block_device_ev3.c

@@ -24,6 +24,7 @@
 
 #include <pbdrv/block_device.h>
 #include <pbdrv/clock.h>
+#include <pbdrv/compiler.h>
 #include <pbdrv/gpio.h>
 
 #include <tiam1808/edma.h>
@@ -486,8 +487,8 @@ static pbio_error_t spi_begin_for_flash(
 
         spi_dev.status = SPI_STATUS_WAIT_TX | SPI_STATUS_WAIT_RX;
 
-        // TODO: pbio probably needs a framework for memory barriers and DMA cache management
-        __asm__ volatile ("" ::: "memory");
+        // TODO: eventually needs DMA cache management
+        pbdrv_compiler_memory_barrier();
 
         EDMA3EnableTransfer(SOC_EDMA30CC_0_REGS, EDMA3_CHA_SPI0_TX, EDMA3_TRIG_MODE_EVENT);
         EDMA3EnableTransfer(SOC_EDMA30CC_0_REGS, EDMA3_CHA_SPI0_RX, EDMA3_TRIG_MODE_EVENT);
@@ -805,8 +806,8 @@ static pbio_error_t pbdrv_block_device_ev3_spi_begin_for_adc(const uint32_t *cmd
 
     spi_dev.status = SPI_STATUS_WAIT_TX | SPI_STATUS_WAIT_RX;
 
-    // TODO: pbio probably needs a framework for memory barriers and DMA cache management
-    __asm__ volatile ("" ::: "memory");
+    // TODO: eventually needs DMA cache management
+    pbdrv_compiler_memory_barrier();
 
     EDMA3EnableTransfer(SOC_EDMA30CC_0_REGS, EDMA3_CHA_SPI0_TX, EDMA3_TRIG_MODE_EVENT);
     EDMA3EnableTransfer(SOC_EDMA30CC_0_REGS, EDMA3_CHA_SPI0_RX, EDMA3_TRIG_MODE_EVENT);

lib/pbio/drv/reset/reset_ev3.c

@@ -9,6 +9,7 @@
 
 #include <stdbool.h>
 
+#include <pbdrv/compiler.h>
 #include <pbdrv/reset.h>
 #include <pbdrv/gpio.h>
 
@@ -63,7 +64,7 @@ void pbdrv_reset(pbdrv_reset_action_t action) {
                 break;
             case PBDRV_RESET_ACTION_RESET_IN_UPDATE_MODE:
                 ev3_persistent_data.bootloader_update_flag = BOOTLOADER_UPDATE_MODE_VALUE;
-                __attribute__((fallthrough));
+                PBDRV_FALL_THROUGH;
             default:
                 // PBDRV_RESET_ACTION_RESET
 

lib/pbio/include/pbdrv/compiler.h

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2025 The Pybricks Authors
+
+#ifndef _PBDRV_COMPILER_H_
+
+// Marks a switch case that intentionally falls through to the next one
+#define PBDRV_FALL_THROUGH                  __attribute__((fallthrough))
+
+// Forces the compiler to not reorder memory access around this line
+#define pbdrv_compiler_memory_barrier()     __asm__ volatile ("" ::: "memory")
+
+#endif