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[PATCH v4 07/21] target/mips/cp0_timer: Document TIMER_PERIOD origin
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From: |
Philippe Mathieu-Daudé |
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Subject: |
[PATCH v4 07/21] target/mips/cp0_timer: Document TIMER_PERIOD origin |
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Date: |
Mon, 12 Oct 2020 11:57:50 +0200 |
TIMER_PERIOD value of '10 ns' can be explained looking at
commit 6af0bf9c7c3doc, where the CPU frequency is 200 MHz
and CP0 default count rate is half the frequency of the
CPU. Document that.
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
target/mips/cp0_timer.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/target/mips/cp0_timer.c b/target/mips/cp0_timer.c
index 5194c967ae3..6fec5fe0ff7 100644
--- a/target/mips/cp0_timer.c
+++ b/target/mips/cp0_timer.c
@@ -27,7 +27,17 @@
#include "sysemu/kvm.h"
#include "internal.h"
-#define TIMER_PERIOD 10 /* 10 ns period for 100 Mhz frequency */
+/*
+ * Since commit 6af0bf9c7c3 this model assumes a CPU clocked at 200MHz
+ * and a CP0 timer running at half the clock of the CPU (cp0_count_rate = 2).
+ *
+ * TIMER_FREQ_HZ = CPU_FREQ_HZ / CP0_COUNT_RATE = 200 MHz / 2 = 100 MHz
+ *
+ * TIMER_PERIOD_NS = 1 / TIMER_FREQ_HZ = 10 ns
+ */
+#define CPU_FREQ_HZ_DEFAULT 200000000
+#define CP0_COUNT_RATE_DEFAULT 2
+#define TIMER_PERIOD 10 /* 1 / (CPU_FREQ_HZ / CP0_COUNT_RATE) */
/* MIPS R4K timer */
static void cpu_mips_timer_update(CPUMIPSState *env)
--
2.26.2
- [PATCH v4 00/21] hw/mips: Set CPU frequency, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 01/21] util/cutils: Introduce freq_to_str() to display Hertz units, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 02/21] qdev-monitor: Display frequencies scaled to SI unit, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 03/21] hw/qdev-clock: Display error hint when clock is missing from device, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 04/21] hw/core/clock: add the clock_new helper function, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 05/21] target/mips: Move cpu_mips_get_random() with CP0 helpers, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 06/21] target/mips/cp0_timer: Explicit unit in variable name, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 07/21] target/mips/cp0_timer: Document TIMER_PERIOD origin,
Philippe Mathieu-Daudé <=
- [PATCH v4 08/21] target/mips: Move cp0_count_ns to CPUMIPSState, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 09/21] target/mips/cpu: Calculate the CP0 timer period using the CPU frequency, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 10/21] target/mips/cpu: Make cp0_count_rate a property, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 11/21] target/mips/cpu: Allow the CPU to use dynamic frequencies, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 12/21] target/mips/cpu: Introduce mips_cpu_create_with_clock() helper, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 13/21] hw/mips/r4k: Explicit CPU frequency is 200 MHz, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 14/21] hw/mips/fuloong2e: Set CPU frequency to 533 MHz, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 15/21] hw/mips/mipssim: Correct CPU frequency, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 16/21] hw/mips/jazz: Correct CPU frequencies, Philippe Mathieu-Daudé, 2020/10/12
- [PATCH v4 17/21] hw/mips/cps: Expose input clock and connect it to CPU cores, Philippe Mathieu-Daudé, 2020/10/12