[Qemu-devel] [PATCH] tmp105: read temperature in milli-celsius

[Paolo Bonzini <pbonzini@redhat.com>]

Right now, the temperature property must be written in milli-celsius, but it
reads back the value in 8.8 fixed point.  Fix this by letting the property
read back the original value (possibly rounded).  Also simplify the code that
does the conversion.

Before:

    (QEMU) qom-set path=/machine/peripheral/sensor property=temperature value=20000
    {u'return': {}}
    (QEMU) qom-get path=sensor property=temperature
    {u'return': 5120}

After:

    (QEMU) qom-set path=/machine/peripheral/sensor property=temperature value=20000
    {u'return': {}}
    (QEMU) qom-get path=sensor property=temperature
    {u'return': 20000}

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/misc/tmp105.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/hw/misc/tmp105.c b/hw/misc/tmp105.c
index 155e03d..63aa3d6 100644
--- a/hw/misc/tmp105.c
+++ b/hw/misc/tmp105.c
@@ -56,12 +56,14 @@ static void tmp105_get_temperature(Object *obj, Visitor *v, void *opaque,
                                    const char *name, Error **errp)
 {
     TMP105State *s = TMP105(obj);
-    int64_t value = s->temperature;
+    int64_t value = s->temperature * 1000 / 256;
 
     visit_type_int(v, &value, name, errp);
 }
 
-/* Units are 0.001 centigrades relative to 0 C.  */
+/* Units are 0.001 centigrades relative to 0 C.  s->temperature is 8.8
+ * fixed point, so units are 1/256 centigrades.  A simple ratio will do.
+ */
 static void tmp105_set_temperature(Object *obj, Visitor *v, void *opaque,
                                    const char *name, Error **errp)
 {
@@ -78,7 +80,7 @@ static void tmp105_set_temperature(Object *obj, Visitor *v, void *opaque,
         return;
     }
 
-    s->temperature = ((int16_t) (temp * 0x800 / 128000)) << 4;
+    s->temperature = (int16_t) (temp * 256 / 1000);
 
     tmp105_alarm_update(s);
 }
-- 
1.8.5.3