stc12a: revamp option handling

Completely revamp option handling. This fixes a wrong index of MCS4,
which is now renamed to MCS3. Now programming should be exactly
similar to STC-ISP 6.85M.

This also renames the values of the low_voltage_reset option for
clarity.

Also update the documentation and clarity the meaning of the option
according to protocol family.

Addresses grigorig/stcgal#14.

README.md

@@ -240,7 +240,9 @@ Option key                    | Possible values   | Protocols/Models    | Descri
 ```ale_enabled```             | true/false        | STC89 only          | ALE pin enabled if true, normal GPIO if false
 ```xram_enabled```            | true/false        | STC89 only          | Use internal XRAM (STC89 only)
 ```watchdog_por_enabled```    | true/false        | All                 | Watchdog state after power-on reset (POR)
-```low_voltage_reset ```      | true/false        | STC12A+             | Low-voltage reset (brownout)
+```low_voltage_reset```       | low/high          | STC12A/STC12        | Low-voltage reset level (low: ~3.3V, high: ~3.7V)
+```low_voltage_reset```       | true/false        | STC12               | Enable RESET2 pin low voltage detect
+```low_voltage_reset```       | true/false        | STC15A              | Enable low-voltage reset (brownout)
 ```clock_source```            | internal/external | STC12A+ with XTAL   | Use internal (RC) or external (crystal) clock
 ```watchdog_stop_idle```      | true/false        | STC12A+             | Stop watchdog in IDLE mode
 ```watchdog_prescale```       | 2,4,8,...,256     | STC12A+             | Watchdog timer prescaler, must be a power of two.

doc/stc12a-options.txt

@@ -4,7 +4,7 @@ Placement of configuration values
 "~" means the bit is a negated boolean. Sometimes values overlap,
 depending on MCU model.
 
-In STC12A series, the first 4 MCS bytes have active
+In STC12A series, the first 7 MCS bytes have active
 values. Generally, unused bits should be set to 1.
 
 MCS0
@@ -47,14 +47,9 @@ MSB     7       6       5       4       3       2       1       0       LSB
          (or others, depends on MCU model) are held low on POR.
 
 
-MCS3
-----
 
-Unused.
-
-
-MCS4
-----
+MCS3 (at index 6!)
+------------------
 
 MSB     7       6       5       4       3       2       1       0       LSB
                 LVD

stcgal/protocols.py

@@ -151,7 +151,7 @@ class Stc12AOption(BaseOption):
     """Manipulate STC12A series option bytes"""
 
     def __init__(self, msr):
-        assert len(msr) == 5
+        assert len(msr) == 4
         self.msr = bytearray(msr)
 
         """list of options and their handlers"""
@@ -166,12 +166,15 @@ class Stc12AOption(BaseOption):
         )
 
     def get_low_voltage_detect(self):
-        return not bool(self.msr[4] & 64)
+        lvd = bool(self.msr[3] & 64)
+        return "high" if not lvd else "low"
 
     def set_low_voltage_detect(self, val):
-        val = Utils.to_bool(val);
-        self.msr[4] &= 0xbf
-        self.msr[4] |= 0x40 if not val else 0x00
+        lvds = {"low": 1, "high": 0}
+        if val not in lvds.keys():
+            raise ValueError("must be one of %s" % list(sources.keys()))
+        self.msr[3] &= 0xbf
+        self.msr[3] |= lvds[val] << 6
 
     def get_clock_source(self):
         source = bool(self.msr[0] & 2)
@@ -1131,6 +1134,8 @@ class Stc12AProtocol(Stc89Protocol):
         self.mcu_bsl_version = "%d.%d%s" % (bl_version >> 4, bl_version & 0x0f,
                                            chr(bl_stepping))
 
+        self.bsl_version = bl_version
+
     def calculate_baud(self):
         """Calculate MCU baudrate setting.
 
@@ -1161,7 +1166,7 @@ class Stc12AProtocol(Stc89Protocol):
         """Initialize options"""
 
         # create option state
-        self.options = Stc12AOption(status_packet[23:28])
+        self.options = Stc12AOption(status_packet[23:26] + status_packet[29:30])
         self.options.print()
 
     def handshake(self):
@@ -1233,14 +1238,28 @@ class Stc12AProtocol(Stc89Protocol):
         print("Setting options: ", end="")
         sys.stdout.flush()
         msr = self.options.get_msr()
-        packet = bytes([0x8d, msr[0], msr[1], msr[2], msr[3],
-                        msr[4]])
-
+        packet = bytes([0x8d, msr[0], msr[1], msr[2], 0xff, msr[3]])
         packet += struct.pack(">I", int(self.mcu_clock_hz))
+        packet += bytes([msr[3]])
+        packet += bytes([0xff, msr[0], msr[1], 0xff, 0xff, 0xff, 0xff, msr[2]])
+        packet += bytes([0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff])
+        packet += struct.pack(">I", int(self.mcu_clock_hz))
+        packet += bytes([0xff, 0xff, 0xff])
+
         self.write_packet(packet)
         response = self.read_packet()
         if response[0] != 0x80:
             raise StcProtocolException("incorrect magic in option packet")
+
+        # XXX: this is done by STC-ISP on newer parts. not sure why, but let's
+        # just replicate it, just to be sure.
+        if self.bsl_version >= 0x66:
+            packet = bytes([0x50])
+            self.write_packet(packet)
+            response = self.read_packet()
+            if response[0] != 0x10:
+                raise StcProtocolException("incorrect magic in option packet")
+
         print("done")