[incubator-nuttx] 02/02: esp32_cpustart.c: Improve comments around the usage of the inter-cpu startup handshake.

[xi...@apache.org]

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commit 50d217a9e86c85f68621a0af470dedb62472e49d
Author: Abdelatif Guettouche <ab...@espressif.com>
AuthorDate: Thu Dec 2 16:34:56 2021 +0100

    esp32_cpustart.c: Improve comments around the usage of the inter-cpu
    startup handshake.
    
    Signed-off-by: Abdelatif Guettouche <ab...@espressif.com>
---
 arch/xtensa/src/esp32/esp32_cpustart.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/xtensa/src/esp32/esp32_cpustart.c b/arch/xtensa/src/esp32/esp32_cpustart.c
index 2ef5358..15afe48 100644
--- a/arch/xtensa/src/esp32/esp32_cpustart.c
+++ b/arch/xtensa/src/esp32/esp32_cpustart.c
@@ -164,7 +164,9 @@ void xtensa_appcpu_start(void)
   sched_note_cpu_started(tcb);
 #endif
 
-  /* Handle interlock */
+  /* Release the spinlock to signal to the PRO CPU that the APP CPU has
+   * started.
+   */
 
   g_appcpu_started = true;
   spin_unlock(&g_appcpu_interlock);
@@ -268,8 +270,9 @@ int up_cpu_start(int cpu)
       sched_note_cpu_start(this_task(), cpu);
 #endif
 
-      /* The waitsem semaphore is used for signaling and, hence, should not
-       * have priority inheritance enabled.
+      /* This spinlock will be used as a handshake between the two CPUs.
+       * It's first initialized to its locked state, later the PRO CPU will
+       * try to lock it but spins until the APP CPU starts and unlocks it.
        */
 
       spin_initialize(&g_appcpu_interlock, SP_LOCKED);
@@ -313,7 +316,7 @@ int up_cpu_start(int cpu)
 
       ets_set_appcpu_boot_addr((uint32_t)xtensa_appcpu_start);
 
-      /* And wait for the initial task to run on CPU1 */
+      /* And wait until the APP CPU starts and releases the spinlock. */
 
       spin_lock(&g_appcpu_interlock);
       DEBUGASSERT(g_appcpu_started);