Add lf em 4x70 autorecover

Also:
* common.h: Increase safety of some of the macros.
  Parenthesizing the macro parameters ... a best practice.
* firmware: partially-tracked source of "extra bits" messages.
  Add a TODO comment for further study.
* Improve reliability of `lf em 4x70 writekey`
  Authenticate w/new key after it is written.
  Particularly important for glass modules,
  or other tags with weaker coupling.

armsrc/em4x70.c

@@ -581,6 +581,11 @@ static bool send_command_and_read(uint8_t command, uint8_t *bytes, size_t length
                 Dbprintf("Invalid data received length: %d, expected %d", len, out_length_bits);
                 return false;
             }
+            // TODO: Figure out why getting an extra bit (quite often) here
+            // e.g., write block and info commands both reach here and output:
+            // [#] Should have a multiple of 8 bits, was sent 33
+            // [#] Should have a multiple of 8 bits, was sent 65
+            // Extra bits are currently just dropped, with no ill effect noticed.
             bits2bytes(bits, len, bytes);
             return true;
         }
@@ -903,10 +908,12 @@ void em4x70_write_key(const em4x70_data_t *etd, bool ledcontrol) {
                     break;
                 }
             }
-            // TODO: Ideally here we would perform a test authentication
+            // The client now has support for test authentication after
-            //       to ensure the new key was written correctly. This is
+            // writing a new key, thus allowing to verify that the new
-            //       what the datasheet suggests. We can't do that until
+            // key was written correctly.  This is what the datasheet
-            //       we have the crypto algorithm implemented.
+            // suggests.   Not currently implemented in the firmware,
+            // although ID48LIB has no dependencies that would prevent
+            // use within the firmware layer.
         }
     }
 

include/common.h

@@ -148,16 +148,16 @@ extern bool g_tearoff_enabled;
 
 // convert 2 bytes to U16 in little endian
 #ifndef BYTES2UINT16
-# define BYTES2UINT16(x) ((x[1] << 8) | (x[0]))
+# define BYTES2UINT16(x) (((x)[1] << 8) | ((x)[0]))
 #endif
 // convert 4 bytes to U32 in little endian
 #ifndef BYTES2UINT32
-# define BYTES2UINT32(x) ((x[3] << 24) | (x[2] << 16) | (x[1] << 8) | (x[0]))
+# define BYTES2UINT32(x) (((x)[3] << 24) | ((x)[2] << 16) | ((x)[1] << 8) | ((x)[0]))
 #endif
 
 // convert 4 bytes to U32 in big endian
 #ifndef BYTES2UINT32_BE
-# define BYTES2UINT32_BE(x) ((x[0] << 24) | (x[1] << 16) | (x[2] << 8) | (x[3]))
+# define BYTES2UINT32_BE(x) (((x)[0] << 24) | ((x)[1] << 16) | ((x)[2] << 8) | ((x)[3]))
 #endif
 
 
@@ -174,7 +174,7 @@ extern bool g_tearoff_enabled;
 #endif
 
 #ifndef CRUMB
-# define CRUMB(b,p)    (((b & (0x3 << p) ) >> p ) & 0xF)
+# define CRUMB(b,p)    ((((b) & (0x3 << (p)) ) >> (p) ) & 0xF)
 #endif
 
 #ifndef SWAP_NIBBLE
@@ -183,18 +183,18 @@ extern bool g_tearoff_enabled;
 
 // Binary Encoded Digit
 #ifndef BCD2DEC
-# define BCD2DEC(bcd) HornerScheme(bcd, 0x10, 10)
+# define BCD2DEC(bcd) HornerScheme((bcd), 0x10, 10)
 #endif
 
 #ifndef DEC2BCD
-# define DEC2BCD(dec) HornerScheme(dec, 10, 0x10)
+# define DEC2BCD(dec) HornerScheme((dec), 10, 0x10)
 #endif
 
 // bit stream operations
-#define TEST_BIT(data, i) (*(data + (i / 8)) >> (7 - (i % 8))) & 1
+#define TEST_BIT(data, i) (*((data) + ((i) / 8)) >> (7 - ((i) % 8))) & 1
-#define SET_BIT(data, i)   *(data + (i / 8)) |= (1 << (7 - (i % 8)))
+#define SET_BIT(data, i)   *((data) + ((i) / 8)) |= (1 << (7 - ((i) % 8)))
-#define CLEAR_BIT(data, i) *(data + (i / 8)) &= ~(1 << (7 - (i % 8)))
+#define CLEAR_BIT(data, i) *((data) + ((i) / 8)) &= ~(1 << (7 - ((i) % 8)))
-#define FLIP_BIT(data, i)  *(data + (i / 8)) ^= (1 << (7 - (i % 8)))
+#define FLIP_BIT(data, i)  *((data) + ((i) / 8)) ^= (1 << (7 - ((i) % 8)))
 
 // time for decompressing and loading the image to the FPGA
 #define FPGA_LOAD_WAIT_TIME (1500)

include/em4x70.h

@@ -39,6 +39,7 @@ typedef struct {
 
     // Used for writing address
     uint8_t address;
+    // ISSUE: Presumes target is little-endian
     uint16_t word;
 
     // PIN to unlock
@@ -53,6 +54,7 @@ typedef struct {
     uint8_t crypt_key[12];
 
     // used for bruteforce the partial key
+    // ISSUE: Presumes target is little-endian
     uint16_t start_key;
 
 } em4x70_data_t;