Update 'dmctl'

dmctl.md

@@ -107,7 +107,48 @@ Temperature sensor I2C device changed from 0x18 to disabled
 
 #### jtag-scan
 
-TODO
+Does a JTAG (or other supported debug interface) scan:
+
+```
+usage: dmctl jtag-scan [-h] {jtag,swd} start end
+
+positional arguments:
+  {jtag,swd}  Pinout type to check for.
+  start       Number of the start of the pin range to scan (inclusive)
+  end         Number of the end of the pin range to scan (inclusive)
+```
+
+```
+$ ./dmctl.sh jtag-scan jtag 10 15
+Starting JTAG scan...
+JTAG scan finished (12 matches):
+Certain matches:
+ 1	TCK=11 TMS=10 TDI=13 TDO=12 nTRST=14 IRLEN=4
+ 2	TCK=11 TMS=10 TDI=13 TDO=12 nTRST=15 IRLEN=4
+
+Possible matches:
+ 3	TCK=11 TMS=10 TDI=14 TDO=12 nTRST=13 #toggle=2
+    <snip>
+ 
+$ ./dmctl.sh jtag-scan swd 10 15
+Starting SWD scan...
+SWD scan finished (1 matches):
+ 1	SWCLK=11 SWDIO=10 idcode=2ba01477
+
+$ ./dmctl.sh jtag-scan swd 15 10
+WARN: start pin 15 greater than end pin 10, swapping the order...
+Starting SWD scan...
+...
+SWD scan finished (1 matches):
+ 1	SWCLK=11 SWDIO=10 idcode=2ba01477
+
+$ ./dmctl.sh jtag-scan swd 0 999
+Start pin must be at least 2, but is 0
+
+$ ./dmctl.sh jtag-scan idk 10 15
+usage: dmctl jtag-scan [-h] {jtag,swd} start end
+dmctl jtag-scan: error: argument type: invalid choice: 'idk' (choose from 'jtag', 'swd')
+```
 
 ### Mode 4-specific subcommands