add BX

TeensyDebug.cpp

@@ -495,6 +495,12 @@ void *instructionBranch(void *p) {
     }
     return (void*)(save_registers.pc + offset);
   }
+  // BX
+  else if ((inst & 0xFF80) == 0x8E00) {
+    int reg = (inst >> 3) & 0b1111;
+    uint32_t addr = getRegisterNum(reg);
+    return (void*)(addr);
+  }
   // BL or BLX prefix
   else if ((inst & 0xF800) == 0xF000) {
     int offset1 = inst & 0x3F;

notes.md

@@ -1,5 +1,5 @@
 
-20200612
+20200613
 
 I put together some code that allows GDB to perform source-level debugging on the Teensy without an external debug interface (no need for SWD, etc). It uses GDB's Remote Serial Protocol to communicate with Teensy over a Serial connection (hardware or USB). This is a beta release for comments and testing. It works (mostly) on Teensy 4 and 3.2. Tested on Mac. Highlights:
 
@@ -7,16 +7,16 @@ I put together some code that allows GDB to perform source-level debugging on th
 * Examine and change memory and registers
 * View call stack
 * Halt code at any time
-* Step with next/step working minimally, but not across functions.
+* Next/step working minimally, but not across functions.
 
-In the past, debugging like this has been very challenging because the debugging features of the Teensy are permanently disabled (see https://forum.pjrc.com/threads/26358-Software-Debugger-Stack and https://forum.pjrc.com/threads/61262-Sleeping-to-disable-C_DEBUGEN?p=242721#post242721). But I'm using a trick that doesn't involve the debugging features.
-
-To emulate breakpoints the library first takes over the SVC interrupt. The Teensy 4 places most code in RAM so to activate a breakpoint it just replaces the original instructions with SVC calls. On Teensy 3.2, setting breakpoints uses the Cortex-M4's features to "patch" parts of flash by pointing it to RAM. 
+To emulate breakpoints the library first takes over the SVC interrupt (like I did in TeensyThreads). The Teensy 4 places most code in RAM so to activate a breakpoint it just replaces the original instructions with SVC calls. On Teensy 3.2, setting breakpoints uses the Cortex-M4's features to "patch" parts of flash by pointing it to RAM. 
 
 The library is enabled by including the header. On Macs, there is a python script that adds a menu option and configures Arduino to open GDB automatically after uploading your program. On other platforms, you run GDB manually and use `target remote` to connect to the serial port used by the GDB interface. However, the python script is simple and could easily be ported to Windows (or rewritten in C).
 
 To read more and try it out visit: http://github.com/ftrias/TeensyDebug
 
+Any comments or code would be greatly appreciated!
+
 20200609
 
 GDB stubs on Teensy