Add software support for PLIC

Author: disdi

sw/c/common/CMakeLists.txt

@@ -1,2 +1,2 @@
-add_library(common OBJECT demo_system.c uart.c timer.c gpio.c pwm.c spi.c crt0.S)
+add_library(common OBJECT demo_system.c uart.c timer.c gpio.c pwm.c spi.c plic.c crt0.S)
 target_include_directories(common INTERFACE "${CMAKE_CURRENT_SOURCE_DIR}")

sw/c/common/demo_system.c

@@ -115,6 +115,36 @@ void set_global_interrupt_enable(uint32_t enable) {
   }
 }
 
+void verify_core_interrupt_enable(void) {
+  uint32_t mstatus, mie;
+
+  // Read mstatus and mie CSRs
+  asm volatile("csrr %0, mstatus" : "=r"(mstatus));
+  asm volatile("csrr %0, mie"     : "=r"(mie));
+
+  puts("MSTATUS: ");
+  puthex(mstatus);
+  putchar('\n');
+
+    // Check global interrupt enable (MIE bit in mstatus, bit 3)
+  if (mstatus & (1 << 3)) {
+      puts("Global interrupts enabled.\n");
+  } else {
+      puts("Global interrupts NOT enabled.\n");
+  }
+
+  puts("MIE: ");
+  puthex(mie);
+  putchar('\n');
+
+  // Check that external interrupts are enabled
+  if (mie & (1 << 11)) {
+      puts("External interrupt (source 11) enabled in MIE.\n");
+  } else {
+      puts("External interrupt (source 11) NOT enabled in MIE.\n");
+  }
+}
+
 void simple_exc_handler(void) {
   puts("EXCEPTION!!!\n");
   puts("============\n");

sw/c/common/demo_system.h

@@ -11,7 +11,9 @@
 #include "gpio.h"
 #include "uart.h"
 
-#define UART_IRQ_NUM 16
+// Changed UART_IRQ_NUM from 16 (fast interrupt) to 11 (external interrupt)
+// External interrupt is bit 11 in the mie register
+#define UART_IRQ_NUM 11
 #define UART_IRQ (1 << UART_IRQ_NUM)
 #define DEFAULT_UART UART_FROM_BASE_ADDR(UART0_BASE)
 
@@ -111,4 +113,6 @@ unsigned int get_mtval();
 uint32_t get_mcycle(void);
 void reset_mcycle(void);
 
+void verify_core_interrupt_enable(void);
+
 #endif

sw/c/common/demo_system_regs.h

@@ -19,4 +19,21 @@
 #define SIM_CTRL_OUT 0x0
 #define SIM_CTRL_CTRL 0x8
 
+// Add PLIC definitions
+#define PLIC_BASE               0x80005000
+
+// PLIC Register offsets
+#define PLIC_PRIORITY_BASE      0x000000
+#define PLIC_PENDING_BASE       0x001000
+#define PLIC_ENABLE_BASE        0x002000
+#define PLIC_THRESHOLD_BASE     0x200000
+#define PLIC_CLAIM_BASE         0x200004
+
+// PLIC configuration
+#define PLIC_MAX_PRIORITY       7
+#define PLIC_PRIORITY_MASK      0x7
+
+// Source IDs
+#define PLIC_SOURCE_UART0       0
+
 #endif

sw/c/common/plic.c

@@ -0,0 +1,55 @@
+#include "plic.h"
+#include "demo_system.h"
+#include "dev_access.h"
+
+void plic_init(void) {
+    // Enable machine external interrupts
+    enable_interrupts(1 << 11);  // Set mie.meie bit
+    
+    // Set threshold to 0 (allow all priorities)
+    plic_set_threshold(0);
+}
+
+void plic_set_priority(uint32_t source, uint32_t priority) {
+    uint32_t addr = PLIC_BASE + PLIC_PRIORITY_BASE + (source * 4);
+    DEV_WRITE(addr, priority & PLIC_PRIORITY_MASK);
+}
+
+void plic_enable_interrupt(uint32_t source) {
+    uint32_t addr = PLIC_BASE + PLIC_ENABLE_BASE;
+    uint32_t current = DEV_READ(addr);
+    DEV_WRITE(addr, current | (1 << source));
+}
+
+void plic_disable_interrupt(uint32_t source) {
+    uint32_t addr = PLIC_BASE + PLIC_ENABLE_BASE;
+    uint32_t current = DEV_READ(addr);
+    DEV_WRITE(addr, current & ~(1 << source));
+}
+
+void plic_set_threshold(uint32_t threshold) {
+    DEV_WRITE(PLIC_BASE + PLIC_THRESHOLD_BASE, threshold & PLIC_PRIORITY_MASK);
+}
+
+uint32_t plic_claim_interrupt(void) {
+    return DEV_READ(PLIC_BASE + PLIC_CLAIM_BASE);
+}
+
+void plic_complete_interrupt(uint32_t source) {
+    DEV_WRITE(PLIC_BASE + PLIC_CLAIM_BASE, source);
+}
+
+void dump_plic_regs(void) {
+  // Read the pending register from the PLIC.
+  uint32_t pending = DEV_READ(PLIC_BASE + PLIC_PENDING_BASE);
+  puts("PLIC pending: ");
+  puthex(pending);
+  putchar('\n');
+
+  // Read the threshold register from the PLIC.
+  uint32_t threshold = DEV_READ(PLIC_BASE + PLIC_THRESHOLD_BASE);
+  puts("PLIC threshold: ");
+  puthex(threshold);
+  putchar('\n');
+}
+  

sw/c/common/plic.h

@@ -0,0 +1,27 @@
+#ifndef PLIC_H__
+#define PLIC_H__
+
+#include <stdint.h>
+
+// Initialize PLIC
+void plic_init(void);
+
+// Set priority for an interrupt source
+void plic_set_priority(uint32_t source, uint32_t priority);
+
+// Enable/disable interrupt source
+void plic_enable_interrupt(uint32_t source);
+void plic_disable_interrupt(uint32_t source);
+
+// Set priority threshold
+void plic_set_threshold(uint32_t threshold);
+
+// Claim and complete interrupts
+uint32_t plic_claim_interrupt(void);
+void plic_complete_interrupt(uint32_t source);
+
+// Check register values
+void dump_plic_regs(void);
+
+
+#endif  // PLIC_H__ 

sw/c/common/uart.c

@@ -8,6 +8,7 @@
 #include "dev_access.h"
 
 void uart_enable_rx_int(void) {
+  // Enable the UART interrupt (now connected to external interrupt)
   enable_interrupts(UART_IRQ);
   set_global_interrupt_enable(1);
 }

sw/c/demo/hello_world/main.c

@@ -8,6 +8,8 @@
 #include "gpio.h"
 #include "pwm.h"
 #include "timer.h"
+#include "plic.h"
+#include "demo_system.h"
 
 #define USE_GPIO_SHIFT_REG 0
 
@@ -24,9 +26,17 @@ void test_uart_irq_handler(void) {
 }
 
 int main(void) {
+  // Install UART interrupt handler using the updated UART_IRQ_NUM (external interrupt)
   install_exception_handler(UART_IRQ_NUM, &test_uart_irq_handler);
   uart_enable_rx_int();
 
+  // Set UART interrupt priority and enable it in the PLIC
+  plic_set_priority(11, 1);
+  plic_enable_interrupt(11);
+
+  // Enable global interrupts
+  set_global_interrupt_enable(1);
+
   // This indicates how often the timer gets updated.
   timer_init();
   timer_enable(5000000);
@@ -54,6 +64,7 @@ int main(void) {
       set_global_interrupt_enable(0);
 
       // Print this to UART (use the screen command to see it).
+
       puts("Hello World! ");
       puthex(last_elapsed_time);
       puts("   Input Value: ");