ARMmbed#112 Add I2C Encoding window command for filesystem parser workaround

Author: gerargz

source/board/microbitv2/i2c_commands.c

@@ -615,6 +615,44 @@ static void i2c_write_flash_callback(uint8_t* pData, uint8_t size) {
                 i2c_fillBuffer((uint8_t*) pI2cCommand, 0, 1);
             }
         break;
+        case gFlashCfgEncWindow_c:
+            if (size == 1) {
+                /* If size is 1 (only cmd id), this means it's a read */
+                uint32_t tempFileEncWindowStart = __REV(gflashConfig.fileEncWindowStart);
+                uint32_t tempFileEncWindowEnd = __REV(gflashConfig.fileEncWindowEnd);
+                i2c_fillBuffer((uint8_t*) pI2cCommand, 0, 1);
+                i2c_fillBuffer((uint8_t*) &tempFileEncWindowStart, 1, sizeof(gflashConfig.fileEncWindowStart));
+                i2c_fillBuffer((uint8_t*) &tempFileEncWindowEnd, 5, sizeof(gflashConfig.fileEncWindowEnd));
+            } else if (size == 9) {
+                /* If size is 9 (cmd id + 8B data), this means it's a write */
+                uint32_t tempFileEncWindowStart = pI2cCommand->cmdData.data[0] << 24 |
+                                        pI2cCommand->cmdData.data[1] << 16 |
+                                        pI2cCommand->cmdData.data[2] << 8 |
+                                        pI2cCommand->cmdData.data[3] << 0;
+                uint32_t tempFileEncWindowEnd = pI2cCommand->cmdData.data[4] << 24 |
+                                        pI2cCommand->cmdData.data[5] << 16 |
+                                        pI2cCommand->cmdData.data[6] << 8 |
+                                        pI2cCommand->cmdData.data[7] << 0;
+                
+                /* Validate encoding window */
+                if (tempFileEncWindowStart <= tempFileEncWindowEnd) {
+                    gflashConfig.fileEncWindowStart = tempFileEncWindowStart;
+                    tempFileEncWindowStart = __REV(gflashConfig.fileEncWindowStart);
+                    gflashConfig.fileEncWindowEnd = tempFileEncWindowEnd;
+                    tempFileEncWindowEnd = __REV(gflashConfig.fileEncWindowEnd);
+                    
+                    i2c_fillBuffer((uint8_t*) pI2cCommand, 0, 1);
+                    i2c_fillBuffer((uint8_t*) &tempFileEncWindowStart, 1, sizeof(gflashConfig.fileEncWindowStart));
+                    i2c_fillBuffer((uint8_t*) &tempFileEncWindowEnd, 5, sizeof(gflashConfig.fileEncWindowEnd));
+                } else {
+                    pI2cCommand->cmdId = gFlashError_c;
+                    i2c_fillBuffer((uint8_t*) pI2cCommand, 0, 1);
+                }
+            } else {
+                pI2cCommand->cmdId = gFlashError_c;
+                i2c_fillBuffer((uint8_t*) pI2cCommand, 0, 1);
+            }
+        break;
         case gFlashCfgFileVisible_c:
             if (size == 1) {
                 /* If size is 1 (only cmd id), this means it's a read */
@@ -658,6 +696,8 @@ static void i2c_write_flash_callback(uint8_t* pData, uint8_t size) {
                 memcpy(gflashConfig.fileName, FLASH_CFG_FILENAME, 11);
                 gflashConfig.fileSize = FLASH_CFG_FILESIZE;
                 gflashConfig.fileVisible = FLASH_CFG_FILEVISIBLE;
+                gflashConfig.fileEncWindowStart = 0;
+                gflashConfig.fileEncWindowEnd = 0;
             }
             i2c_fillBuffer((uint8_t*) pI2cCommand, 0, 1);
         break;

source/board/microbitv2/i2c_commands.h

@@ -124,6 +124,8 @@ typedef __PACKED_STRUCT flashConfig_tag {
     vfs_filename_t  fileName;
     uint32_t        fileSize;
     bool            fileVisible;
+    uint32_t        fileEncWindowStart;
+    uint32_t        fileEncWindowEnd;
 } flashConfig_t;
 
 /*! Flash interface command type */
@@ -136,6 +138,7 @@ typedef enum flashCmdId_tag {
     gFlashStorageSize_c     = 0x06,
     gFlashSectorSize_c      = 0x07,
     gFlashRemountMSD_c      = 0x08,
+    gFlashCfgEncWindow_c    = 0x09,
     gFlashDataRead_c        = 0x0A,
     gFlashDataWrite_c       = 0x0B,
     gFlashDataErase_c       = 0x0C,

source/board/microbitv2/microbitv2.c

@@ -71,6 +71,8 @@ flashConfig_t gflashConfig = {
     .fileName = FLASH_CFG_FILENAME,
     .fileSize = FLASH_CFG_FILESIZE,
     .fileVisible = FLASH_CFG_FILEVISIBLE,
+    .fileEncWindowStart = 0,
+    .fileEncWindowEnd = 0,
 };
 
 typedef enum {
@@ -528,7 +530,8 @@ void vfs_user_build_filesystem_hook() {
         }
     }
 
-    file_size = gflashConfig.fileSize;
+    // Add encoding window file size. 1B encoded into 2B ASCII
+    file_size = gflashConfig.fileSize + (gflashConfig.fileEncWindowEnd - gflashConfig.fileEncWindowStart);
 
     if (gflashConfig.fileVisible) {
         vfs_create_file(gflashConfig.fileName, read_file_data_txt, 0, file_size);
@@ -538,9 +541,32 @@ void vfs_user_build_filesystem_hook() {
 // File callback to be used with vfs_add_file to return file contents
 static uint32_t read_file_data_txt(uint32_t sector_offset, uint8_t *data, uint32_t num_sectors)
 {
+    uint32_t read_address = FLASH_STORAGE_ADDRESS + (VFS_SECTOR_SIZE * sector_offset);
+    uint32_t encoded_data_offset = (gflashConfig.fileEncWindowEnd - gflashConfig.fileEncWindowStart);
+    
     // Ignore out of bound reads
-    if ( (FLASH_STORAGE_ADDRESS + VFS_SECTOR_SIZE * sector_offset) < (FLASH_CONFIG_ADDRESS + FLASH_INTERFACE_SIZE) ) {
-        memcpy(data, (uint8_t *) (FLASH_STORAGE_ADDRESS + VFS_SECTOR_SIZE * sector_offset), VFS_SECTOR_SIZE);
+    if ( read_address < (FLASH_CONFIG_ADDRESS + FLASH_INTERFACE_SIZE + encoded_data_offset) ) {
+        for (uint32_t i = 0; i < VFS_SECTOR_SIZE; i++) {
+            if (i + (VFS_SECTOR_SIZE * sector_offset) < gflashConfig.fileEncWindowStart) {
+                // If data is before encoding window, no offset is needed
+                data[i] = *(uint8_t *) (read_address + i);
+            } else if(i + (VFS_SECTOR_SIZE * sector_offset) < (gflashConfig.fileEncWindowStart + encoded_data_offset * 2)) {
+                // Data inside encoding window needs to consider encoding window start and size
+                uint8_t enc_byte = *(uint8_t *) (FLASH_STORAGE_ADDRESS + ((VFS_SECTOR_SIZE * sector_offset) + gflashConfig.fileEncWindowStart + i ) / 2);
+                if (i % 2 == 0) {
+                    // High nibble
+                    enc_byte = 0x0F & (enc_byte >> 4);
+                } else {
+                    // Low nibble
+                    enc_byte = 0x0F & enc_byte;
+                }
+                // Encode one nibble to one ASCII byte
+                data[i] = enc_byte <= 9 ? enc_byte + 0x30 : enc_byte + 0x37;
+            } else {
+                // If data is after encoding window, adjustment is needed
+                data[i] = *(uint8_t *) (read_address + i - encoded_data_offset);
+            }
+        }
     }
 
     return VFS_SECTOR_SIZE;