From ce175df376222b42a658769e90ca4752ccb90403 Mon Sep 17 00:00:00 2001
From: David Cermak <cermak@espressif.com>
Date: Fri, 16 Sep 2022 16:17:01 +0200
Subject: [PATCH] fix(esp_modem): CMUX to ignore MSC frames

Otherwise it gets confused with DISC frame and causes trouble when entering
CMUX mode (if device sends MSC requests)

Closes https://github.com/espressif/esp-protocols/issues/140
---
 components/esp_modem/src/esp_modem_cmux.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/components/esp_modem/src/esp_modem_cmux.cpp b/components/esp_modem/src/esp_modem_cmux.cpp
index 0243a4991..743371a99 100644
--- a/components/esp_modem/src/esp_modem_cmux.cpp
+++ b/components/esp_modem/src/esp_modem_cmux.cpp
@@ -143,6 +143,10 @@ void CMux::data_available(uint8_t *data, size_t len)
 #endif
         }
     } else if ((type&FT_UIH) == FT_UIH && dlci == 0) { // notify the internal DISC command
+        if (len > 0 && (data[0] & 0xE1) == 0xE1) {
+            // Not a DISC, ignore (MSC frame)
+            return;
+        }
         Scoped<Lock> l(lock);
         sabm_ack = dlci;
     }
@@ -385,6 +389,9 @@ bool CMux::init()
                 return false;
             }
         }
+        if (i > 1) {    // wait for each virtual terminal to settle MSC (no need for control term, DLCI=0)
+            usleep(100'000);
+        }
     }
     return true;
 }