CI: Fix LLVM build failures and test timeouts

This commit resolves two critical issues identified in CI:
1. LLVM Toolchain Detection
- Problem: TOOLCHAIN_TYPE environment variable from CI wasn't being used
- The build system only relied on auto-detection via CC_IS_CLANG
- Result: All LLVM builds failed with "build_failed" status
- Fix: Check TOOLCHAIN_TYPE=llvm before auto-detection
2. Mutex Functional Test Timeout
- Problem: Test exceeded 5-second timeout before printing PASS criteria
- Monitor task ran 50 cycles with excessive yields (5 per cycle)
- Each task iteration had 3 cooperation yields + 3 work yields

Author: jserv

app/mutex.c

@@ -6,7 +6,7 @@
 
 /* Test configuration */
 #define MAX_ITERATIONS 5
-#define COOPERATION_YIELDS 3 /* Number of yields between iterations */
+#define COOPERATION_YIELDS 1 /* Number of yields between iterations */
 
 /* Shared resources protected by binary semaphore */
 static sem_t *binary_mutex = NULL;
@@ -35,8 +35,7 @@ void task_a(void)
         int old_counter = shared_counter;
 
         /* Simulate work with yields instead of delays */
-        for (int work = 0; work < 3; work++)
-            mo_task_yield();
+        mo_task_yield();
 
         shared_counter = old_counter + 1;
         task_a_count++;
@@ -95,8 +94,7 @@ void task_b(void)
         int old_counter = shared_counter;
 
         /* Simulate work */
-        for (int work = 0; work < 3; work++)
-            mo_task_yield();
+        mo_task_yield();
 
         shared_counter = old_counter + 10;
         task_b_count++;
@@ -134,11 +132,11 @@ void monitor_task(void)
 
     int cycles = 0;
 
-    while (cycles < 50) { /* Monitor for reasonable time */
+    while (cycles < 20) { /* Monitor for reasonable time */
         cycles++;
 
         /* Check progress every few cycles */
-        if (cycles % 10 == 0) {
+        if (cycles % 4 == 0) {
             printf("Monitor: A=%d, B=%d, Counter=%d, Violations=%d\n",
                    task_a_count, task_b_count, shared_counter,
                    critical_section_violations);
@@ -151,7 +149,7 @@ void monitor_task(void)
         }
 
         /* Yield to let other tasks run */
-        for (int i = 0; i < 5; i++)
+        for (int i = 0; i < 2; i++)
             mo_task_yield();
     }
 

arch/riscv/build.mk

@@ -19,8 +19,15 @@ DEFINES := -DF_CPU=$(F_CLK) \
 
 CROSS_COMPILE ?= riscv-none-elf-
 
-# Detect LLVM/Clang toolchain (allow user override)
-CC_IS_CLANG ?= $(shell $(CROSS_COMPILE)clang --version 2>/dev/null | grep -qi clang && echo 1)
+# Detect LLVM/Clang toolchain
+# Priority: TOOLCHAIN_TYPE env var > CC_IS_CLANG var > auto-detection
+ifeq ($(TOOLCHAIN_TYPE),llvm)
+    CC_IS_CLANG := 1
+    # Export for sub-makes
+    export TOOLCHAIN_TYPE
+else
+    CC_IS_CLANG ?= $(shell $(CROSS_COMPILE)clang --version 2>/dev/null | grep -qi clang && echo 1)
+endif
 
 # Architecture flags
 ARCH_FLAGS = -march=rv32imzicsr -mabi=ilp32