diff --git a/components/newlib/test/test_time.c b/components/newlib/test/test_time.c
new file mode 100644
index 000000000..a230a220b
--- /dev/null
+++ b/components/newlib/test/test_time.c
@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <math.h>
+#include "unity.h"
+#include "driver/adc.h"
+#include <time.h>
+#include <sys/time.h>
+#include "soc/rtc_cntl_reg.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "freertos/semphr.h"
+#include "sdkconfig.h"
+
+
+// https://github.com/espressif/arduino-esp32/issues/120
+TEST_CASE("Reading RTC registers on APP CPU doesn't affect clock", "[newlib]")
+{
+    // This runs on APP CPU:
+    void time_adc_test_task(void* arg)
+    {
+        for (int i = 0; i < 200000; ++i) {
+            // wait for 20us, reading one of RTC registers
+            uint32_t ccount = xthal_get_ccount();
+            while (xthal_get_ccount() - ccount < 20 * CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ) {
+                volatile uint32_t val = REG_READ(RTC_CNTL_STATE0_REG);
+                (void) val;
+            }
+        }
+        SemaphoreHandle_t * p_done = (SemaphoreHandle_t *) arg;
+        xSemaphoreGive(*p_done);
+        vTaskDelay(1);
+        vTaskDelete(NULL);
+    }
+
+    SemaphoreHandle_t done = xSemaphoreCreateBinary();
+    xTaskCreatePinnedToCore(&time_adc_test_task, "time_adc", 4096, &done, 5, NULL, 1);
+
+    // This runs on PRO CPU:
+    for (int i = 0; i < 4; ++i) {
+        struct timeval tv_start;
+        gettimeofday(&tv_start, NULL);
+        vTaskDelay(1000/portTICK_PERIOD_MS);
+        struct timeval tv_stop;
+        gettimeofday(&tv_stop, NULL);
+        float time_sec = tv_stop.tv_sec - tv_start.tv_sec + 1e-6f * (tv_stop.tv_usec - tv_start.tv_usec);
+        printf("(0) time taken: %f sec\n", time_sec);
+        TEST_ASSERT_TRUE(fabs(time_sec - 1.0f) < 0.1);
+    }
+    TEST_ASSERT_TRUE(xSemaphoreTake(done, 5000 / portTICK_RATE_MS));
+}
+
diff --git a/components/newlib/time.c b/components/newlib/time.c
index c9fa72eee..30c7ca7f4 100644
--- a/components/newlib/time.c
+++ b/components/newlib/time.c
@@ -83,12 +83,18 @@ static volatile uint64_t s_microseconds = 0;
 
 static void IRAM_ATTR frc_timer_isr()
 {
+    // Write to FRC_TIMER_INT_REG may not take effect in some cases (root cause TBD)
+    // This extra write works around this issue.
+    // There is no register at DR_REG_FRC_TIMER_BASE + 0x60 (in fact, any DPORT register address can be used).
+    WRITE_PERI_REG(DR_REG_FRC_TIMER_BASE + 0x60, 0xabababab);
+    // Clear interrupt status
     WRITE_PERI_REG(FRC_TIMER_INT_REG(0), FRC_TIMER_INT_CLR);
     s_microseconds += FRC1_ISR_PERIOD_US;
 }
 
 #endif // WITH_FRC1
 
+#if defined(WITH_RTC) || defined(WITH_FRC1)
 static void set_boot_time(uint64_t time_us)
 {
     _lock_acquire(&s_boot_time_lock);
@@ -113,6 +119,7 @@ static uint64_t get_boot_time()
     _lock_release(&s_boot_time_lock);
     return result;
 }
+#endif //defined(WITH_RTC) || defined(WITH_FRC1)
 
 void esp_setup_time_syscalls()
 {