[Qemu-devel] [PATCH v2 5/6] hw/ds1338.c: Implement support for the control register.

[Antoine Mathys <barsamin@gmail.com>]

The previous patch has the side effect of clearing the control register. 
That's already its proper power-on-reset value.

Signed-off-by: Antoine Mathys <barsamin@gmail.com>
---
  hw/ds1338.c |   17 +++++++++++++----
  1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/hw/ds1338.c b/hw/ds1338.c
index 5a6234b..319c341 100644
--- a/hw/ds1338.c
+++ b/hw/ds1338.c
@@ -125,7 +125,8 @@ static int ds1338_send(I2CSlave *i2c, uint8_t data)
          s->addr_byte = false;
          return 0;
      }
-    if (s->ptr < 8) {
+    if (s->ptr < 7) {
+        /* Time register. */
          struct tm now;
          qemu_get_timedate(&now, s->offset);
          switch(s->ptr) {
@@ -162,11 +163,19 @@ static int ds1338_send(I2CSlave *i2c, uint8_t data)
          case 6:
              now.tm_year = from_bcd(data) + 100;
              break;
-        case 7:
-            /* Control register. Currently ignored.  */
-            break;
          }
          s->offset = qemu_timedate_diff(&now);
+    } else if (s->ptr == 7) {
+        /* Control register. */
+
+        /* Ensure bits 2, 3 and 6 will read back as zero. */
+        data &= 0xB3;
+
+        /* Attempting to write the OSF flag to logic 1 leaves the
+           value unchanged. */
+        data = (data & ~CTRL_OSF) | (data & s->nvram[s->ptr] & CTRL_OSF);
+
+        s->nvram[s->ptr] = data;
      } else {
          s->nvram[s->ptr] = data;
      }
-- 
1.7.10.4