Add sw 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.h

@@ -26,6 +26,23 @@
 
 #define DEFAULT_SPI SPI_FROM_BASE_ADDR(SPI0_BASE)
 
+// 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
+
 /**
  * Writes character to default UART. Signature matches c stdlib function
  * of the same name.

sw/c/common/plic.c

@@ -0,0 +1,40 @@
+#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);
+} 

sw/c/common/plic.h

@@ -0,0 +1,23 @@
+#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);
+
+#endif  // PLIC_H__ 

sw/c/common/uart.c

@@ -6,9 +6,16 @@
 
 #include "demo_system.h"
 #include "dev_access.h"
+#include "plic.h"
 
 void uart_enable_rx_int(void) {
-  enable_interrupts(UART_IRQ);
+  // Set UART interrupt priority (e.g., priority 2)
+  plic_set_priority(PLIC_SOURCE_UART0, 2);
+  
+  // Enable UART interrupt in PLIC
+  plic_enable_interrupt(PLIC_SOURCE_UART0);
+  
+  // Enable global interrupts
   set_global_interrupt_enable(1);
 }
 

sw/c/demo/hello_world/main.c

@@ -8,22 +8,31 @@
 #include "gpio.h"
 #include "pwm.h"
 #include "timer.h"
+#include "plic.h"
 
 #define USE_GPIO_SHIFT_REG 0
 
 void test_uart_irq_handler(void) __attribute__((interrupt));
 
 void test_uart_irq_handler(void) {
-  int uart_in_char;
-
-  while ((uart_in_char = uart_in(DEFAULT_UART)) != -1) {
-    uart_out(DEFAULT_UART, uart_in_char);
-    uart_out(DEFAULT_UART, '\r');
-    uart_out(DEFAULT_UART, '\n');
+  uint32_t source = plic_claim_interrupt();
+  
+  if (source == PLIC_SOURCE_UART0) {
+    int uart_in_char;
+    while ((uart_in_char = uart_in(DEFAULT_UART)) != -1) {
+      uart_out(DEFAULT_UART, uart_in_char);
+      uart_out(DEFAULT_UART, '\r');
+      uart_out(DEFAULT_UART, '\n');
+    }
+    plic_complete_interrupt(source);
   }
 }
 
 int main(void) {
+  // Initialize PLIC
+  plic_init();
+  
+  // Install exception handlers
   install_exception_handler(UART_IRQ_NUM, &test_uart_irq_handler);
   uart_enable_rx_int();