altos/lisp: Append a CRC to the saved image to validate on restore

[fw/altos] / src / lisp / ao_lisp_make_const.c

diff --git a/src/lisp/ao_lisp_make_const.c b/src/lisp/ao_lisp_make_const.c
index 0a8c9d0752ce6603a40695b56d68406416819077..6a29f402d263cfbe5e11ae478089cb8440c1b9ce 100644 (file)
--- a/src/lisp/ao_lisp_make_const.c
+++ b/src/lisp/ao_lisp_make_const.c
@@ -86,6 +86,33 @@ is_atom(int offset)
        return 0;
 }
 
+#define AO_FEC_CRC_INIT        0xffff
+
+static inline uint16_t
+ao_fec_crc_byte(uint8_t byte, uint16_t crc)
+{
+       uint8_t bit;
+
+       for (bit = 0; bit < 8; bit++) {
+               if (((crc & 0x8000) >> 8) ^ (byte & 0x80))
+                       crc = (crc << 1) ^ 0x8005;
+               else
+                       crc = (crc << 1);
+               byte <<= 1;
+       }
+       return crc;
+}
+
+uint16_t
+ao_fec_crc(const uint8_t *bytes, uint8_t len)
+{
+       uint16_t        crc = AO_FEC_CRC_INIT;
+
+       while (len--)
+               crc = ao_fec_crc_byte(*bytes++, crc);
+       return crc;
+}
+
 int
 main(int argc, char **argv)
 {
@@ -126,6 +153,7 @@ main(int argc, char **argv)
        printf("extern const uint8_t ao_lisp_const[AO_LISP_POOL_CONST] __attribute__((aligned(4)));\n");
        printf("#define ao_builtin_atoms 0x%04x\n", ao_lisp_atom_poly(ao_lisp_atoms));
        printf("#define ao_builtin_frame 0x%04x\n", ao_lisp_frame_poly(ao_lisp_frame_global));
+       printf("#define ao_lisp_const_checksum ((uint16_t) 0x%04x)\n", ao_fec_crc(ao_lisp_const, ao_lisp_top));
 
        for (a = ao_lisp_atoms; a; a = ao_lisp_poly_atom(a->next)) {
                char    *n = a->name, c;