From 165319c3bd3f50a39b0b053b2ddf3f3aed5bbbab Mon Sep 17 00:00:00 2001
From: Matteo Golin <matteo.golin@gmail.com>
Date: Wed, 15 Jan 2025 14:22:37 -0500
Subject: [PATCH] Fix CRC and test on Raspberry Pi Pico

---
 .../rp2040/common/src/rp2040_common_bringup.c | 16 +++++++++++
 include/nuttx/sensors/msxxxx_crc4.h           | 27 +++++++++----------
 2 files changed, 29 insertions(+), 14 deletions(-)

diff --git a/boards/arm/rp2040/common/src/rp2040_common_bringup.c b/boards/arm/rp2040/common/src/rp2040_common_bringup.c
index 136d4178d4810..e17dd8b9aa1a8 100644
--- a/boards/arm/rp2040/common/src/rp2040_common_bringup.c
+++ b/boards/arm/rp2040/common/src/rp2040_common_bringup.c
@@ -73,6 +73,11 @@
 #include "rp2040_i2c.h"
 #endif
 
+#ifdef CONFIG_SENSORS_MS56XX
+#include <nuttx/sensors/ms56xx.h>
+#include "rp2040_i2c.h"
+#endif
+
 #ifdef CONFIG_SENSORS_MAX6675
 #include <nuttx/sensors/max6675.h>
 #include "rp2040_max6675.h"
@@ -508,6 +513,17 @@ int rp2040_common_bringup(void)
     }
 #endif
 
+
+#ifdef CONFIG_SENSORS_MS56XX
+  /* Try to register MS56xx device at I2C0 */
+  ret = ms56xx_register(rp2040_i2cbus_initialize(0), 0, MS56XX_ADDR0,
+                        MS56XX_MODEL_MS5611);
+  if (ret < 0)
+    {
+        syslog(LOG_ERR, "ERROR: couldn't register MS5611: %d\n", ret);
+    }
+#endif
+
 #ifdef CONFIG_VIDEO_FB
   ret = fb_register(0, 0);
   if (ret < 0)
diff --git a/include/nuttx/sensors/msxxxx_crc4.h b/include/nuttx/sensors/msxxxx_crc4.h
index e1bf0b6cc723b..0101e34f969e3 100644
--- a/include/nuttx/sensors/msxxxx_crc4.h
+++ b/include/nuttx/sensors/msxxxx_crc4.h
@@ -43,42 +43,41 @@ static uint8_t msxxxx_crc4(FAR uint16_t *src,
                            uint8_t crcndx,
                            uint16_t crcmask)
 {
-  uint16_t cnt;
-  uint16_t n_rem;
-  uint16_t crc_read;
+  uint16_t cnt;       /* simple counter */
+  uint16_t n_rem;     /* crc reminder */
+  uint16_t crc_read;  /* original value of the crc */
   uint8_t n_bit;
 
   n_rem = 0x00;
-  crc_read = src[crcndx];
-  src[crcndx] &= ~crcmask;
+  crc_read = src[crcndx];   /* save read CRC */
+  src[crcndx] &= ~crcmask;  /* CRC byte is replaced by 0 */
 
-  for (cnt = 0; cnt < 16; cnt++)
+  for (cnt = 0; cnt < 16; cnt++)  /* operation is performed on bytes */
     {
       if (cnt % 2 == 1)
         {
-          n_rem ^= src[cnt >> 1] & 0x00ff;
+          n_rem ^= (uint16_t)((src[cnt >> 1]) & 0x00ff);
         }
       else
         {
-          n_rem ^= src[cnt >> 1] >> 8;
+          n_rem ^= (uint16_t)(src[cnt >> 1] >> 8);
         }
 
       for (n_bit = 8; n_bit > 0; n_bit--)
         {
-          if (n_rem & (0x8000) != 0)
+          if (n_rem & (0x8000))
             {
               n_rem = (n_rem << 1) ^ 0x3000;
             }
           else
             {
-              n_rem <<= 1;
+              n_rem = (n_rem << 1);
             }
         }
     }
-
-  n_rem = (n_rem >> 12) & 0x000f;
-  src[crcndx] = crc_read;
-  return n_rem ^ 0x00;
+  n_rem = (0x000f & (n_rem >> 12));  /* final 4-bit reminder is CRC code */
+  src[crcndx] = crc_read;            /* restore the crc_read to its original place */
+  return (n_rem ^ 0x00);
 }
 
 #endif /* __INCLUDE_NUTTX_SENSORS_MSXXXX_CRC4_H */