Courtesy of Yann:

Bugfix: Special registers for address mode matching only worked with lower case register names.
Bugfix: movem with pc-relative mode was missing for weird immediate mode.
Bugfix: btst with pc-relative and weird immediate mode was missing.
Enhancement: Assembler syntax with implicit immediate 1 for shifts and rotations no longer cause syntax errors.

src/test/java/de/platon42/intellij/plugins/m68k/parser/AddressingModesTest.kt

@@ -87,6 +87,11 @@ internal class AddressingModesTest : AbstractParsingTest() {
         testGoodSyntax(testCase, " move.l 4.w,a6\n")
     }
 
+    @Test
+    internal fun btst_quirk(@MyTestCase testCase: ParsingTestExtension.IParsingTestCase) {
+        testGoodSyntax(testCase, " btst #5,#42\n btst d0,#42")
+    }
+
     @Test
     internal fun movem_register_list(@MyTestCase testCase: ParsingTestExtension.IParsingTestCase) {
         testGoodSyntax(testCase, " movem.l d0-d2/d4/a0/a2-a3/a5,-(sp)\n")
@@ -118,7 +123,7 @@ internal class AddressingModesTest : AbstractParsingTest() {
     internal fun special_register_move(@MyTestCase testCase: ParsingTestExtension.IParsingTestCase) {
         testGoodSyntax(
             testCase, " move.l usp,a0\n"
-                    + " move.l a5,usp\n"
+                    + " move.l a5,USP\n"
         )
     }
 

src/test/resources/parser/addressingmodes/btst_quirk.txt

@@ -0,0 +1,31 @@
+Assembly File: a.asm
+  PsiWhiteSpace(' ')
+  M68kStatementImpl(STATEMENT)
+    M68kAsmInstructionImpl(ASM_INSTRUCTION)
+      M68kAsmOpImpl(ASM_OP)
+        PsiElement(M68kTokenType.MNEMONIC)('btst')
+      PsiWhiteSpace(' ')
+      M68kImmediateDataImpl(IMMEDIATE_DATA)
+        PsiElement(M68kTokenType.HASH)('#')
+        M68kLiteralExprImpl(LITERAL_EXPR)
+          PsiElement(M68kTokenType.DECIMAL)('5')
+      PsiElement(M68kTokenType.SEPARATOR)(',')
+      M68kImmediateDataImpl(IMMEDIATE_DATA)
+        PsiElement(M68kTokenType.HASH)('#')
+        M68kLiteralExprImpl(LITERAL_EXPR)
+          PsiElement(M68kTokenType.DECIMAL)('42')
+  PsiElement(M68kTokenType.EOL)('\n')
+  PsiWhiteSpace(' ')
+  M68kStatementImpl(STATEMENT)
+    M68kAsmInstructionImpl(ASM_INSTRUCTION)
+      M68kAsmOpImpl(ASM_OP)
+        PsiElement(M68kTokenType.MNEMONIC)('btst')
+      PsiWhiteSpace(' ')
+      M68kDataRegisterDirectAddressingModeImpl(DATA_REGISTER_DIRECT_ADDRESSING_MODE)
+        M68kDataRegisterImpl(DATA_REGISTER)
+          PsiElement(M68kTokenType.DREG)('d0')
+      PsiElement(M68kTokenType.SEPARATOR)(',')
+      M68kImmediateDataImpl(IMMEDIATE_DATA)
+        PsiElement(M68kTokenType.HASH)('#')
+        M68kLiteralExprImpl(LITERAL_EXPR)
+          PsiElement(M68kTokenType.DECIMAL)('42')

src/test/resources/parser/addressingmodes/special_register_move.txt

@@ -29,5 +29,5 @@ Assembly File: a.asm
       PsiElement(M68kTokenType.SEPARATOR)(',')
       M68kSpecialRegisterDirectAddressingModeImpl(SPECIAL_REGISTER_DIRECT_ADDRESSING_MODE)
         M68kSpecialRegisterImpl(SPECIAL_REGISTER)
-          PsiElement(M68kTokenType.REG_USP)('usp')
+          PsiElement(M68kTokenType.REG_USP)('USP')
   PsiElement(M68kTokenType.EOL)('\n')