From c8ca5406518d1f13c996b143863da1a1328fcfa2 Mon Sep 17 00:00:00 2001
From: Eirik Stople <eirik@pcfood.net>
Date: Sun, 26 May 2024 22:29:25 +0200
Subject: [PATCH] Disable PS2 pullup when power supply is off

This is to prevent trying to power the keyboard via the PS2 ports when the
power supply is off.
---
 ps2.h       | 13 +++++++++++--
 x16-smc.ino | 21 ++++++++++++++++++---
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/ps2.h b/ps2.h
index 3fc4efc..fa5800a 100644
--- a/ps2.h
+++ b/ps2.h
@@ -4,6 +4,8 @@
 #include "optimized_gpio.h"
 #define SCANCODE_TIMEOUT_MS 50
 
+bool PWR_ON_active();
+
 enum PS2_CMD_STATUS : uint8_t {
   IDLE = 0,
   CMD_PENDING = 1,
@@ -44,8 +46,15 @@ class PS2Port
     };
 
     virtual void resetInput() {
-      gpio_inputWithPullup(datPin);
-      gpio_inputWithPullup(clkPin);
+      if (PWR_ON_active()) {
+        gpio_inputWithPullup(datPin);
+        gpio_inputWithPullup(clkPin);
+      } else {
+        // Prevent powering the keyboard via the pull-ups when system is off
+        // Call reset() after changing PWR_ON
+        pinMode_opt(datPin, INPUT);
+        pinMode_opt(clkPin, INPUT);
+      }
       curCode = 0;
       parity = 0;
       rxBitCount = 0;
diff --git a/x16-smc.ino b/x16-smc.ino
index 0a1ad42..7ff7d60 100644
--- a/x16-smc.ino
+++ b/x16-smc.ino
@@ -171,8 +171,8 @@ void setup() {
 
   // Setup Power Supply
   pinMode_opt(PWR_OK, INPUT);
-  pinMode_opt(PWR_ON, OUTPUT);
   digitalWrite_opt(PWR_ON, HIGH);
+  pinMode_opt(PWR_ON, OUTPUT);
 
   // Turn Off Activity LED
   pinMode_opt(ACT_LED, OUTPUT);
@@ -317,6 +317,8 @@ void PowerOffSeq() {
   digitalWrite_opt(ACT_LED, ACT_LED_OFF);     // Ensure activity LED is off
   _delay_ms(AUDIOPOP_HOLDTIME_MS);                // Wait for audio system to stabilize before power is turned off
   digitalWrite_opt(PWR_ON, HIGH);             // Turn off supply
+  Keyboard.reset();                           // Reset and deactivate pullup
+  Mouse.reset();                              // Reset and deactivate pullup
   SYSTEM_POWERED = 0;                         // Global Power state Off
   _delay_ms(RESB_HOLDTIME_MS);                    // Mostly here to add some delay between presses
   deassertReset();
@@ -325,6 +327,8 @@ void PowerOffSeq() {
 void PowerOnSeq() {
   assertReset();
   digitalWrite_opt(PWR_ON, LOW);              // turn on power supply
+  Keyboard.reset();                           // Reset and activate pullup
+  Mouse.reset();                              // Reset and activate pullup
   unsigned long TimeDelta = 0;
   unsigned long StartTime = millis();         // get current time
   while (!digitalRead_opt(PWR_OK)) {          // Time how long it takes
@@ -336,8 +340,6 @@ void PowerOnSeq() {
     // insert error handler, flash activity light & Halt?   IE, require hard power off before continue?
   }
   else {
-    Keyboard.flush();
-    Mouse.reset();
     defaultRequest = I2C_CMD_GET_KEYCODE_FAST;
     _delay_ms(RESB_HOLDTIME_MS);                // Allow system to stabilize
     SYSTEM_POWERED = 1;                     // Global Power state On
@@ -594,3 +596,16 @@ ISR(TIMER1_COMPA_vect) {
   Keyboard.timerInterrupt();
   Mouse.timerInterrupt();
 }
+
+bool PWR_ON_active()
+{
+  // Returns the status of the PWR_ON output port.
+  // PWR_ON is active low.
+  // Thus, return true if DDR is output (1) and if PORT is low (0).
+  // Similar to the SYSTEM_POWERED variable, but this is more accurate when power is changing.
+  // A future code improvement can be to make gpio functions to read from PORT/DDR register
+  // PWR_ON is 5, which is PA5
+
+  if ((DDRA & _BV(5)) == 0) return false; // Port is input. This is the case when mouse and keyboard objects are created
+  return (PORTA & _BV(5)) ? false : true;
+}