mimxrt/sdcard: Add cache coherency operations for DMA transfers.

Add explicit data cache management to ensure DMA transfers work correctly
on systems with data cache enabled (e.g., MIMXRT1170).

For writes: Clean cache to RAM before transfer so DMA reads correct data.

For reads: Clean and invalidate cache before transfer, then invalidate
again after transfer completes to discard any speculative cache line
fills that may have occurred during the DMA.

Also fix writeblocks to use MP_BUFFER_READ (reading from buffer to write
to card) and update read/writeblocks to raise OSError on failure.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

ports/mimxrt/machine_sdcard.c

@@ -104,12 +104,10 @@ static mp_obj_t machine_sdcard_readblocks(mp_obj_t self_in, mp_obj_t block_num,
     mp_buffer_info_t bufinfo;
     mimxrt_sdcard_obj_t *self = MP_OBJ_TO_PTR(self_in);
     mp_get_buffer_raise(buf, &bufinfo, MP_BUFFER_WRITE);
-
-    if (sdcard_read(self, bufinfo.buf, mp_obj_get_int(block_num), bufinfo.len / SDCARD_DEFAULT_BLOCK_SIZE)) {
-        return MP_OBJ_NEW_SMALL_INT(0);
-    } else {
-        return MP_OBJ_NEW_SMALL_INT(-MP_EIO);
+    if (!sdcard_read(self, bufinfo.buf, mp_obj_get_int(block_num), bufinfo.len / SDCARD_DEFAULT_BLOCK_SIZE)) {
+        mp_raise_OSError(MP_EIO);
     }
+    return mp_const_none;
 }
 static MP_DEFINE_CONST_FUN_OBJ_3(machine_sdcard_readblocks_obj, machine_sdcard_readblocks);
 
@@ -142,13 +140,11 @@ static MP_DEFINE_CONST_FUN_OBJ_1(machine_sdcard_info_obj, machine_sdcard_info);
 static mp_obj_t machine_sdcard_writeblocks(mp_obj_t self_in, mp_obj_t block_num, mp_obj_t buf) {
     mp_buffer_info_t bufinfo;
     mimxrt_sdcard_obj_t *self = MP_OBJ_TO_PTR(self_in);
-    mp_get_buffer_raise(buf, &bufinfo, MP_BUFFER_WRITE);
-
-    if (sdcard_write(self, bufinfo.buf, mp_obj_get_int(block_num), bufinfo.len / SDCARD_DEFAULT_BLOCK_SIZE)) {
-        return MP_OBJ_NEW_SMALL_INT(0);
-    } else {
-        return MP_OBJ_NEW_SMALL_INT(-MP_EIO);
+    mp_get_buffer_raise(buf, &bufinfo, MP_BUFFER_READ);
+    if (!sdcard_write(self, bufinfo.buf, mp_obj_get_int(block_num), bufinfo.len / SDCARD_DEFAULT_BLOCK_SIZE)) {
+        mp_raise_OSError(MP_EIO);
     }
+    return mp_const_none;
 }
 static MP_DEFINE_CONST_FUN_OBJ_3(machine_sdcard_writeblocks_obj, machine_sdcard_writeblocks);
 

ports/mimxrt/sdcard.c

@@ -867,11 +867,19 @@ void sdcard_init_pins(mimxrt_sdcard_obj_t *card) {
     }
 }
 
+// Note on buffer alignment: The cache operations extend to 32-byte (cache line) boundaries.
+// For buffers that are part of larger structures, this could affect adjacent memory.
+// The MicroPython VFS layer typically provides properly allocated buffers that are safe.
+// DMA requires 4-byte alignment which is checked implicitly by the hardware.
 bool sdcard_read(mimxrt_sdcard_obj_t *card, uint8_t *buffer, uint32_t block_num, uint32_t block_count) {
     if (!card->state->initialized) {
         return false;
     }
 
+    // Ensure cache is flushed and invalidated so when DMA updates RAM
+    // from the peripheral, the CPU reads the new data.
+    MP_HAL_CLEANINVALIDATE_DCACHE(buffer, block_count * card->block_len);
+
     usdhc_data_t data = {
         .enableAutoCommand12 = true,
         .enableAutoCommand23 = false,
@@ -900,17 +908,23 @@ bool sdcard_read(mimxrt_sdcard_obj_t *card, uint8_t *buffer, uint32_t block_num,
 
     if (status == kStatus_Success) {
         card->status = command.response[0];
+        // Invalidate cache again after DMA completes to discard any speculative
+        // cache line fills that may have occurred during the transfer.
+        MP_HAL_CLEANINVALIDATE_DCACHE(buffer, block_count * card->block_len);
         return true;
     } else {
         return false;
     }
 }
 
-bool sdcard_write(mimxrt_sdcard_obj_t *card, uint8_t *buffer, uint32_t block_num, uint32_t block_count) {
+bool sdcard_write(mimxrt_sdcard_obj_t *card, const uint8_t *buffer, uint32_t block_num, uint32_t block_count) {
     if (!card->state->initialized) {
         return false;
     }
 
+    // Ensure cache is flushed to RAM so DMA can read the correct data.
+    MP_HAL_CLEAN_DCACHE(buffer, block_count * card->block_len);
+
     usdhc_data_t data = {
         .enableAutoCommand12 = true,
         .enableAutoCommand23 = false,

ports/mimxrt/sdcard.h

@@ -99,7 +99,7 @@ void sdcard_init(mimxrt_sdcard_obj_t *card, uint32_t base_clk);
 void sdcard_deinit(mimxrt_sdcard_obj_t *card);
 void sdcard_init_pins(mimxrt_sdcard_obj_t *card);
 bool sdcard_read(mimxrt_sdcard_obj_t *card, uint8_t *buffer, uint32_t block_num, uint32_t block_count);
-bool sdcard_write(mimxrt_sdcard_obj_t *card, uint8_t *buffer, uint32_t block_num, uint32_t block_count);
+bool sdcard_write(mimxrt_sdcard_obj_t *card, const uint8_t *buffer, uint32_t block_num, uint32_t block_count);
 bool sdcard_set_active(mimxrt_sdcard_obj_t *card);
 bool sdcard_volt_validation(mimxrt_sdcard_obj_t *card);
 bool sdcard_power_on(mimxrt_sdcard_obj_t *self);