Differences

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--- controllers [2022/06/11 14:37] – [Flow control] admin
+++ controllers [2023/06/05 19:59] (current) – [Checksum/keepalive] simer
@@ Line 40: / Line 40: @@
   * Make sure the reply is completely sent ("Tx buffer empty" in status register)
   * Check that RTS did not become low
-  * Put CTS high again
+  * Put CTS low again
   * Back to idle state
 The controller keeps RTS down as long as it has more bytes to send.
+{{::04_idle_mergedbytes.png?nolink|}}
 ===== Messages from the controller =====
@@ Line 78: / Line 80: @@
 | Right          | C3 80 to C7 80  | C0 80              |
+The controller also sends Bx values for keepalive (see below).
 ==== Dance mat ====
@@ Line 143: / Line 146: @@
   * 0x44: German
 ===== Commands from the console =====
-is sent during boot to start the controller.
 , 62, 64 and 68 are sent in reply to color buttons presses. I suspect this controls the lights in the buttons.
 is sent to turn the light off.
-These are repeated every 20ms. After the controller sends 55 (idle), the V.Smile also returns to its idle reply (E6 for example) every 20ms.
+These are repeated every 20ms. After the controller sends 55 (idle), the game also returns to its idle reply (E6 followed by D6 for example) every 20ms.
+==== Checksum/keepalive ====
+The console sends 7x commands (where x is a "random" number) periodically and expects Bx replies from the controller.
+The controller response algorithm to compute the correct reply is:
+''0xb0 | (((A + B + 0x0f) & 0x0f) ^ 0x05)''
+where A and B are the two most recent lower nibbles sent by the console in 7x commands. If only one nibble has been sent, the other nibble in the algorithm will have 0 as its value. The console can also reset the previous state by sending a Bx command instead which otherwise works like a 7x command.
+The console must send the 7x commands, even if it ignores all the Bx replies from the controller. Without these commands, the controller eventually shuts down.