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[PATCH v2 07/20] target/mips/cp0_timer: Document TIMER_PERIOD origin
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From: |
Philippe Mathieu-Daudé |
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Subject: |
[PATCH v2 07/20] target/mips/cp0_timer: Document TIMER_PERIOD origin |
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Date: |
Sat, 10 Oct 2020 19:26:04 +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 v2 00/20] hw/mips: Set CPU frequency, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 01/20] util/cutils: Introduce freq_to_str() to display Hertz units, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 02/20] qdev-monitor: Display frequencies scaled to SI unit, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 03/20] hw/qdev-clock: Display error hint when clock is missing from device, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 04/20] hw/core/clock: add the clock_new helper function, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 06/20] target/mips/cp0_timer: Explicit unit in variable name, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 05/20] target/mips: Move cpu_mips_get_random() with CP0 helpers, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 07/20] target/mips/cp0_timer: Document TIMER_PERIOD origin,
Philippe Mathieu-Daudé <=
- [PATCH v2 08/20] target/mips: Move cp0_count_ns to CPUMIPSState, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 09/20] target/mips/cpu: Calculate the CP0 timer period using the CPU frequency, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 11/20] target/mips/cpu: Allow the CPU to use dynamic frequencies, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 10/20] target/mips/cpu: Make cp0_count_rate a property, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 14/20] hw/mips/mipssim: Correct CPU frequency, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 13/20] hw/mips/fuloong2e: Set CPU frequency to 533 MHz, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 12/20] hw/mips/r4k: Explicit CPU frequency is 200 MHz, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 18/20] hw/mips/malta: Set CPU frequency to 320 MHz, Philippe Mathieu-Daudé, 2020/10/10
- [PATCH v2 17/20] hw/mips/boston: Set CPU frequency to 1 GHz, Philippe Mathieu-Daudé, 2020/10/10