altos/drivers: Shrink ao_ms5607.c code to fit on micropeak still

Use some code constructs that make the little AVR processor happier
and save about 16 bytes of memory.

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/drivers/ao_ms5607.c b/src/drivers/ao_ms5607.c
index 914e0c1b3c7b620ca40c23ee82f88c9ac5b5576e..3b3381ef0a3453ac32b790763b4b737a2627f118 100644 (file)
--- a/src/drivers/ao_ms5607.c
+++ b/src/drivers/ao_ms5607.c
@@ -57,10 +57,11 @@ ao_ms5607_crc(uint8_t *prom)
        uint8_t         cnt;
        uint16_t        n_rem = 0;
        uint8_t         n_bit;
+       uint8_t         *p = prom;
 
        prom[15] = 0;
        for (cnt = 0; cnt < 16; cnt++) {
-               n_rem ^= prom[cnt];
+               n_rem ^= *p++;
                for (n_bit = 8; n_bit > 0; n_bit--) {
                        if (n_rem & 0x8000)
                                n_rem = (n_rem << 1) ^ 0x3000;
@@ -73,12 +74,33 @@ ao_ms5607_crc(uint8_t *prom)
        return n_rem;
 }
 
+static int
+ao_ms5607_prom_valid(uint8_t *prom)
+{
+       uint8_t crc;
+       int     i;
+       uint8_t *p;
+
+       /* Look for a value other than 0x0000 or 0xffff */
+       p = prom;
+       for (i = 0; i < 16; i++)
+               if (*p++ + 1 > 1)
+                       break;
+       if (i == 16)
+               return false;
+
+       crc = ao_ms5607_crc(prom);
+       if (crc != (prom[15] & 0xf))
+               return false;
+
+       return true;
+}
+
 static void
 ao_ms5607_prom_read(__xdata struct ao_ms5607_prom *prom)
 {
-       uint8_t                 addr;
-       uint8_t                 crc;
-       __xdata uint16_t        *r;
+       uint8_t         addr;
+       uint16_t        *r;
 
        r = (__xdata uint16_t *) prom;
        for (addr = 0; addr < 8; addr++) {
@@ -89,22 +111,19 @@ ao_ms5607_prom_read(__xdata struct ao_ms5607_prom *prom)
                ao_ms5607_stop();
                r++;
        }
-       crc = ao_ms5607_crc((uint8_t *) prom);
-       if (crc != (((uint8_t *) prom)[15] & 0xf)) {
-#if HAS_TASK
-               printf ("MS5607 PROM CRC error (computed %x actual %x)\n",
-                       crc, (((uint8_t *) prom)[15] & 0xf));
-               flush();
-#endif
+
+       if (!ao_ms5607_prom_valid((uint8_t *) prom))
                ao_panic(AO_PANIC_SELF_TEST_MS5607);
-       }
 
 #if __BYTE_ORDER == __LITTLE_ENDIAN
        /* Byte swap */
        r = (uint16_t *) prom;
        for (addr = 0; addr < 8; addr++) {
-               uint16_t        t = *r;
-               *r++ = (t << 8) | (t >> 8);
+               uint8_t         *t = (uint8_t *) r;
+               uint8_t a = t[0];
+               t[0] = t[1];
+               t[1] = a;
+               r++;
        }
 #endif
 }