From 923e9d39a02698e5a3c5e2bac25c30839f8bb8f7 Mon Sep 17 00:00:00 2001
From: vhaudiquet <vhaudiquet343@hotmail.fr>
Date: Fri, 3 Nov 2023 11:25:58 +0100
Subject: [PATCH] Better exception/interrupt handle

---
 src/cpu/exception.c |  8 ++++++--
 src/cpu/interrupt.c | 48 +++++++++++++++++++++++++++------------------
 src/cpu/rv32cpu.c   |  9 +++++++--
 3 files changed, 42 insertions(+), 23 deletions(-)

diff --git a/src/cpu/exception.c b/src/cpu/exception.c
index f2db177..cf22c99 100644
--- a/src/cpu/exception.c
+++ b/src/cpu/exception.c
@@ -15,6 +15,8 @@ __attribute__((noreturn)) void exception_trigger(rv32_cpu_t* cpu, uint32_t scaus
 
 	// Exceptions cannot be disabled
 
+	// TODO : Check medeleg to see if we should handle exception in S mode or M mode
+
 	// Unset SIE (interrupt enable) bit
 	csr_write(cpu, CSR_SSTATUS, csr_read(cpu, CSR_SSTATUS) & (~STATUS_SIE));
 
@@ -37,8 +39,10 @@ __attribute__((noreturn)) void exception_trigger(rv32_cpu_t* cpu, uint32_t scaus
 		csr_write(cpu, CSR_SSTATUS, csr_read(cpu, CSR_SSTATUS) & (~STATUS_SPIE));
 
 	// Set previous privilege mode in xSTATUS.xPP
-	// TODO : Allow user mode exceptions (by not setting this)
-	csr_write(cpu, CSR_SSTATUS, csr_read(cpu, CSR_SSTATUS) | STATUS_SPP);
+	if(cpu->privilege_mode == SUPERVISOR)
+		csr_write(cpu, CSR_SSTATUS, csr_read(cpu, CSR_SSTATUS) | STATUS_SPP);
+	else if(cpu->privilege_mode == USER)
+		csr_write(cpu, CSR_SSTATUS, csr_read(cpu, CSR_SSTATUS) & (~STATUS_SPP));
 
 	// Set privilege mode for exception handling, checking for delegation
 	// TODO
diff --git a/src/cpu/interrupt.c b/src/cpu/interrupt.c
index ed34b0d..65871a5 100644
--- a/src/cpu/interrupt.c
+++ b/src/cpu/interrupt.c
@@ -4,28 +4,38 @@
 #include <stdio.h>
 #include <unistd.h>
 
-void interrupt_trigger(rv32_cpu_t* cpu, uint32_t scause)
+uint32_t interrupt_mi_from_scause(uint32_t scause)
 {
-	// Make sure that interrupts are enabled
-	if(cpu->privilege_mode == MACHINE)
-	{
-		// In machine mode, we check mstatus.sie (bit 1)
-		if(!(cpu->csr[CSR_MSTATUS] & 0b10))
-			return;
-	}
-	else if(cpu->privilege_mode == SUPERVISOR)
+	switch(scause)
 	{
-		// In supervisor mode, we check sstatus.sie (bit 1)
-		if(!(cpu->csr[CSR_SSTATUS] & 0b10))
-			return;
+		case SCAUSE_SUPERVISOR_TIMER_INTERRUPT:
+			return 0x20;
+		default:
+			fprintf(stderr, "interrupt_mie_bit_from_scause: wrong scause 0x%x\n", scause);
+			exit(EXIT_FAILURE);
 	}
-	else
+
+	return 0;
+}
+
+void interrupt_trigger(rv32_cpu_t* cpu, uint32_t scause)
+{
+	// Make sure that interrupts are enabled globally
+	if(!(csr_read(cpu, CSR_MSTATUS) & STATUS_SIE))
+		return;
+
+	// Make sure that current interrupt is enabled
+	if(!(csr_read(cpu, CSR_MIE) & interrupt_mi_from_scause(scause)))
 	{
-		// TODO
-		fprintf(stderr, "interrupt_trigger in non M/S-mode not implemented yet\n");
-		exit(EXIT_FAILURE);
+		// Mark interrupt as pending
+		csr_write(cpu, CSR_MIP, csr_read(cpu, CSR_MIP) | interrupt_mi_from_scause(scause));
+
+		return;
 	}
 
+	// TODO : CHECK mideleg to see wether we should handle interrupt is S mode or M mode
+	
+
 	// An interrupt can only be triggered from outside
 	// of the cpu, so we are on a different thread
 	// and we don't already own the CPU mutex
@@ -39,14 +49,14 @@ void interrupt_trigger(rv32_cpu_t* cpu, uint32_t scause)
 	cpu->csr[CSR_SCAUSE] = 0x80000000 | scause;
 
 	// Set xSTATUS.xPIE (previous interrupt enable) bit
-	cpu->csr[CSR_SSTATUS] |= 0x80;
+	cpu->csr[CSR_MSTATUS] |= STATUS_SPIE;
 
 	// Set xSTATUS.xPP (Previous Privilege) bit
 	// TODO : Allow user mode interrupts (by not setting this)
-	cpu->csr[CSR_SSTATUS] |= 0x100;
+	cpu->csr[CSR_MSTATUS] |= 0x100;
 
 	// Unset xSTATUS.xIE (interrupt enable) bit
-	cpu->csr[CSR_SSTATUS] &= ~0b10U;
+	cpu->csr[CSR_MSTATUS] &= (~STATUS_SIE);
 
 	// Set xEPC : PC at interruption
 	cpu->csr[CSR_SEPC] = cpu->pc;
diff --git a/src/cpu/rv32cpu.c b/src/cpu/rv32cpu.c
index a28c51a..30bc5f8 100644
--- a/src/cpu/rv32cpu.c
+++ b/src/cpu/rv32cpu.c
@@ -533,13 +533,18 @@ static void cpu_execute(rv32_cpu_t* cpu, instruction_t* instruction)
 								csr_write(cpu, CSR_SSTATUS, csr_read(cpu, CSR_SSTATUS) | STATUS_SIE);
 
 							// Restore privilege mode from Previous Privilege
-							// TODO
+							if(!(csr_read(cpu, CSR_SSTATUS) & STATUS_SPP))
+							{
+								// Previous Privilege was 0, return to user mode
+								fprintf(stderr, "SRET to user mode : not implemented yet\n");
+								exit(EXIT_FAILURE);
+							}
 
 							// Set Previous Interrupt Enable to 1
 							csr_write(cpu, CSR_SSTATUS, csr_read(cpu, CSR_SSTATUS) | STATUS_SPIE);
 
 							// Set Previous Privilege to 0
-							// TODO
+							csr_write(cpu, CSR_SSTATUS, csr_read(cpu, CSR_SSTATUS) & (~STATUS_SPP));
 
 							// Saved PC before interrupt is in CSR SEPC, jump back
 							cpu->pc = csr_read(cpu, CSR_SEPC) - 4;