rtc: implement century byte

Implement the century byte in the RTC emulation, and test that it works.
This leads to some annoying compatibility code because we need to treat
a value of 2000 for the base_year property as "use the century byte
properly" (which would be a value of 0).

The century byte will now be always-zero, rather than always-20,
for the MIPS Magnum machine whose base_year is 1980.  Commit 42fc73a
(Support epoch of 1980 in RTC emulation for MIPS Magnum, 2009-01-24)
correctly said:

    With an epoch of 1980 and a year of 2009, one could argue that [the
    century byte] should hold either 0, 1, 19 or 20.  NT 3.50 on MIPS
    does not read the century byte.

so I picked the simplest and most sensible implementation which is to
return 0 for 1980-2079, 1 for 2080-2179 and so on.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 30 insertions, 2 deletions

diff --git a/tests/rtc-test.c b/tests/rtc-test.c
index 2b9aa63c1f..7fdc94a3de 100644
--- a/tests/rtc-test.c
+++ b/tests/rtc-test.c
@@ -179,12 +179,13 @@ static void check_time(int wiggle)
 
 static int wiggle = 2;
 
-static void set_year(void)
+static void set_year_20xx(void)
 {
     /* Set BCD mode */
     cmos_write(RTC_REG_B, cmos_read(RTC_REG_B) & ~REG_B_DM);
     cmos_write(RTC_REG_A, 0x76);
     cmos_write(RTC_YEAR, 0x11);
+    cmos_write(RTC_CENTURY, 0x20);
     cmos_write(RTC_MONTH, 0x02);
     cmos_write(RTC_DAY_OF_MONTH, 0x02);
     cmos_write(RTC_HOURS, 0x02);
@@ -198,6 +199,7 @@ static void set_year(void)
     g_assert_cmpint(cmos_read(RTC_DAY_OF_MONTH), ==, 0x02);
     g_assert_cmpint(cmos_read(RTC_MONTH), ==, 0x02);
     g_assert_cmpint(cmos_read(RTC_YEAR), ==, 0x11);
+    g_assert_cmpint(cmos_read(RTC_CENTURY), ==, 0x20);
 
     /* Set a date in 2080 to ensure there is no year-2038 overflow.  */
     cmos_write(RTC_REG_A, 0x76);
@@ -210,6 +212,7 @@ static void set_year(void)
     g_assert_cmpint(cmos_read(RTC_DAY_OF_MONTH), ==, 0x02);
     g_assert_cmpint(cmos_read(RTC_MONTH), ==, 0x02);
     g_assert_cmpint(cmos_read(RTC_YEAR), ==, 0x80);
+    g_assert_cmpint(cmos_read(RTC_CENTURY), ==, 0x20);
 
     cmos_write(RTC_REG_A, 0x76);
     cmos_write(RTC_YEAR, 0x11);
@@ -221,6 +224,30 @@ static void set_year(void)
     g_assert_cmpint(cmos_read(RTC_DAY_OF_MONTH), ==, 0x02);
     g_assert_cmpint(cmos_read(RTC_MONTH), ==, 0x02);
     g_assert_cmpint(cmos_read(RTC_YEAR), ==, 0x11);
+    g_assert_cmpint(cmos_read(RTC_CENTURY), ==, 0x20);
+}
+
+static void set_year_1980(void)
+{
+    /* Set BCD mode */
+    cmos_write(RTC_REG_B, cmos_read(RTC_REG_B) & ~REG_B_DM);
+    cmos_write(RTC_REG_A, 0x76);
+    cmos_write(RTC_YEAR, 0x80);
+    cmos_write(RTC_CENTURY, 0x19);
+    cmos_write(RTC_MONTH, 0x02);
+    cmos_write(RTC_DAY_OF_MONTH, 0x02);
+    cmos_write(RTC_HOURS, 0x02);
+    cmos_write(RTC_MINUTES, 0x04);
+    cmos_write(RTC_SECONDS, 0x58);
+    cmos_write(RTC_REG_A, 0x26);
+
+    g_assert_cmpint(cmos_read(RTC_HOURS), ==, 0x02);
+    g_assert_cmpint(cmos_read(RTC_MINUTES), ==, 0x04);
+    g_assert_cmpint(cmos_read(RTC_SECONDS), >=, 0x58);
+    g_assert_cmpint(cmos_read(RTC_DAY_OF_MONTH), ==, 0x02);
+    g_assert_cmpint(cmos_read(RTC_MONTH), ==, 0x02);
+    g_assert_cmpint(cmos_read(RTC_YEAR), ==, 0x80);
+    g_assert_cmpint(cmos_read(RTC_CENTURY), ==, 0x19);
 }
 
 static void bcd_check_time(void)
@@ -313,7 +340,8 @@ int main(int argc, char **argv)
     qtest_add_func("/rtc/bcd/check-time", bcd_check_time);
     qtest_add_func("/rtc/dec/check-time", dec_check_time);
     qtest_add_func("/rtc/alarm-time", alarm_time);
-    qtest_add_func("/rtc/set-year", set_year);
+    qtest_add_func("/rtc/set-year/20xx", set_year_20xx);
+    qtest_add_func("/rtc/set-year/1980", set_year_1980);
     qtest_add_func("/rtc/fuzz-registers", fuzz_registers);
     ret = g_test_run();