From 300965ab10720cd4de300879b85b73a33f56d701 Mon Sep 17 00:00:00 2001
From: joevt <joevt@shaw.ca>
Date: Mon, 7 Aug 2023 11:11:02 -0700
Subject: [PATCH] Decrementer exception changes.

---
 cpu/ppc/ppcemu.h          |  2 ++
 cpu/ppc/ppcexceptions.cpp |  2 +-
 cpu/ppc/ppcexec.cpp       |  5 ++++-
 cpu/ppc/ppcopcodes.cpp    | 47 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/cpu/ppc/ppcemu.h b/cpu/ppc/ppcemu.h
index 816af8d..c327546 100644
--- a/cpu/ppc/ppcemu.h
+++ b/cpu/ppc/ppcemu.h
@@ -173,6 +173,7 @@ extern uint64_t rtc_timestamp;
 extern uint64_t tbr_wr_value;
 extern uint32_t dec_wr_value;
 extern uint32_t tbr_freq_ghz;
+extern uint64_t tbr_period_ns;
 extern uint32_t rtc_lo, rtc_hi;
 
 // Additional steps to prevent overflow?
@@ -319,6 +320,7 @@ extern bool grab_return;
 
 extern bool power_on;
 extern bool int_pin;
+extern bool dec_exception_pending;
 
 extern bool is_601;        // For PowerPC 601 Emulation
 extern bool is_altivec;    // For Altivec Emulation
diff --git a/cpu/ppc/ppcexceptions.cpp b/cpu/ppc/ppcexceptions.cpp
index cec9632..11c6a0c 100644
--- a/cpu/ppc/ppcexceptions.cpp
+++ b/cpu/ppc/ppcexceptions.cpp
@@ -131,7 +131,7 @@ void ppc_exception_handler(Except_Type exception_type, uint32_t srr1_bits) {
 
     mmu_change_mode();
 
-    if (exception_type != Except_Type::EXC_EXT_INT) {
+    if (exception_type != Except_Type::EXC_EXT_INT && exception_type != Except_Type::EXC_DECR) {
         longjmp(exc_env, 2); /* return to the main execution loop. */
     }
 }
diff --git a/cpu/ppc/ppcexec.cpp b/cpu/ppc/ppcexec.cpp
index 9d7971a..70ac292 100644
--- a/cpu/ppc/ppcexec.cpp
+++ b/cpu/ppc/ppcexec.cpp
@@ -55,6 +55,7 @@ uint32_t ppc_next_instruction_address;    // Used for branching, setting up the
 
 unsigned exec_flags;  // execution control flags
 bool int_pin = false; // interrupt request pin state: true - asserted
+bool dec_exception_pending = false;
 
 /* copy of local variable bb_start_la. Need for correct
    calculation of CPU cycles after setjmp that clobbers
@@ -69,7 +70,8 @@ int      icnt_factor;
 uint64_t tbr_wr_timestamp;  // stores vCPU virtual time of the last TBR write
 uint64_t rtc_timestamp;     // stores vCPU virtual time of the last RTC write
 uint64_t tbr_wr_value;      // last value written to the TBR
-uint32_t tbr_freq_ghz;      // TBR/RTC driving frequency in GHz expressed as a 32 bit fraction less than 1.0.
+uint32_t tbr_freq_ghz;      // TBR/RTC driving frequency in GHz expressed as a 32 bit fraction less than 1.0 (999.999999 MHz maximum).
+uint64_t tbr_period_ns;     // TBR/RTC period in ns expressed as a 64 bit value with 32 fractional bits (<1 Hz minimum).
 uint64_t timebase_counter;  // internal timebase counter
 uint64_t dec_wr_timestamp;  // stores vCPU virtual time of the last DEC write
 uint32_t dec_wr_value;      // last value written to the DEC register
@@ -768,6 +770,7 @@ void ppc_cpu_init(MemCtrlBase* mem_ctrl, uint32_t cpu_version, uint64_t tb_freq)
     rtc_timestamp = 0;
     tbr_wr_value = 0;
     tbr_freq_ghz = (tb_freq << 32) / NS_PER_SEC;
+    tbr_period_ns = ((uint64_t)NS_PER_SEC << 32) / tb_freq;
 
     exec_flags = 0;
 
diff --git a/cpu/ppc/ppcopcodes.cpp b/cpu/ppc/ppcopcodes.cpp
index 3960099..07eeabf 100644
--- a/cpu/ppc/ppcopcodes.cpp
+++ b/cpu/ppc/ppcopcodes.cpp
@@ -851,6 +851,10 @@ void dppc_interpreter::ppc_mtmsr() {
     if (ppc_state.msr & 0x8000 && int_pin) {
         LOG_F(WARNING, "MTMSR: CPU INT pending, generate CPU exception");
         ppc_exception_handler(Except_Type::EXC_EXT_INT, 0);
+    } else if ((ppc_state.msr & 0x8000) && dec_exception_pending) {
+        dec_exception_pending = false;
+        //LOG_F(WARNING, "MTMSR: decrementer exception triggered");
+        ppc_exception_handler(Except_Type::EXC_DECR, 0);
     } else {
         mmu_change_mode();
     }
@@ -894,9 +898,43 @@ static void update_timebase(uint64_t mask, uint64_t new_val)
     tbr_wr_timestamp = get_virt_time_ns();
 }
 
+
+static uint32_t decrementer_timer_id = 0;
+
+static void trigger_decrementer_exception() {
+    decrementer_timer_id = 0;
+    dec_wr_value = -1;
+    dec_wr_timestamp = get_virt_time_ns();
+    if (ppc_state.msr & 0x8000) {
+        dec_exception_pending = false;
+        //LOG_F(WARNING, "decrementer exception triggered");
+        ppc_exception_handler(Except_Type::EXC_DECR, 0);
+    }
+    else {
+        //LOG_F(WARNING, "decrementer exception pending");
+        dec_exception_pending = true;
+    }
+}
+
 static void update_decrementer(uint32_t val) {
     dec_wr_value = val;
     dec_wr_timestamp = get_virt_time_ns();
+
+    dec_exception_pending = false;
+
+    if (decrementer_timer_id) {
+        //LOG_F(WARNING, "decrementer cancel timer");
+        TimerManager::get_instance()->cancel_timer(decrementer_timer_id);
+    }
+
+    uint64_t time_out;
+    uint32_t time_out_lo;
+    _u32xu64(val, tbr_period_ns, time_out, time_out_lo);
+    //LOG_F(WARNING, "decrementer:0x%08X ns:%llu", val, time_out);
+    decrementer_timer_id = TimerManager::get_instance()->add_oneshot_timer(
+        time_out,
+        trigger_decrementer_exception
+    );
 }
 
 void dppc_interpreter::ppc_mfspr() {
@@ -1401,6 +1439,15 @@ void dppc_interpreter::ppc_rfi() {
         return;
     }
 
+    if ((ppc_state.msr & 0x8000) && dec_exception_pending) {
+        dec_exception_pending = false;
+        //LOG_F(WARNING, "decrementer exception from rfi msr:0x%X", ppc_state.msr);
+        uint32_t save_srr0 = ppc_state.spr[SPR::SRR0] & 0xFFFFFFFCUL;
+        ppc_exception_handler(Except_Type::EXC_DECR, 0);
+        ppc_state.spr[SPR::SRR0] = save_srr0;
+        return;
+    }
+
     ppc_next_instruction_address = ppc_state.spr[SPR::SRR0] & 0xFFFFFFFCUL;
 
     do_ctx_sync(); // RFI is context synchronizing