From f7493de0b0c587fa87a59c8001f35155d35509a1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Niklas=20Ekstr=C3=B6m?= <mail@niklasekstrom.nu>
Date: Thu, 22 Jul 2021 21:48:59 +0200
Subject: [PATCH] Revert pin assignment of BUSY and POUT signals

The assignment of the BUSY and POUT pins to the microcontroller had
changed from the previous version to the new version. User amigos500 on
the a1k forum noted that if the assignment of those two pins had not
changed, then it would be easier to patch an old PCB to work with
the updated design.

After testing, it seems that the old pin assignment of BUSY and POUT
works equally well with the updated design, and I therefore reverted
the assignment back.
---
 avr/main.c                        | 36 +++++++++++++++----------------
 hardware/assembly-instructions.md |  4 ++--
 2 files changed, 19 insertions(+), 21 deletions(-)

diff --git a/avr/main.c b/avr/main.c
index dabd098..9c250ca 100644
--- a/avr/main.c
+++ b/avr/main.c
@@ -15,8 +15,8 @@
 // 8    D6      D6      PD6
 // 9    D7      D7      PD7
 // 10   ACK     D9      PB1             IRQ     Interrupt request to Amiga
-// 11   BUSY    D8      PB0             ACT     Indicate command running
-// 12   POUT    D4      PD4             CLK     Clock to advance command
+// 11   BUSY    D4      PD4             ACT     Indicate command running
+// 12   POUT    D5      PD5             CLK     Clock to advance command
 // 13   SEL     D2      PD2             REQ     Amiga wants to execute command
 //              D3      PD3     CD      CP      Card Present
 //              D10     PB2     SS
@@ -30,10 +30,10 @@
 #define MOSI_BIT        3 // Output.
 #define SS_BIT_n        2 // Output, active low.
 #define IRQ_BIT_n       1 // Output, active low, open collector.
-#define ACT_BIT_n       0 // Output, active low.
 
 // Pins in port D.
-#define CLK_BIT         4 // Input.
+#define CLK_BIT         5 // Input.
+#define ACT_BIT_n       4 // Output, active low.
 #define CP_BIT_n        3 // Input, active low, internal pull-up enabled.
 #define REQ_BIT_n       2 // Input, active low, internal pull-up enabled.
 
@@ -52,7 +52,7 @@ void start_command()
     {
         byte_count = cval;
 
-        PORTB &= ~(1 << ACT_BIT_n);
+        PORTD &= ~(1 << ACT_BIT_n);
 
         if (dval & 0x40)
             goto do_read;
@@ -63,7 +63,7 @@ void start_command()
     {
         byte_count = cval << 7;
 
-        PORTB &= ~(1 << ACT_BIT_n);
+        PORTD &= ~(1 << ACT_BIT_n);
 
         if (dval & (1 << CLK_BIT))
         {
@@ -95,12 +95,12 @@ void start_command()
             else // Deselect
                 PORTB |= (1 << SS_BIT_n);
 
-            PORTB &= ~(1 << ACT_BIT_n);
+            PORTD &= ~(1 << ACT_BIT_n);
         }
         else if (cmd == 1) // CARD_PRESENT
         {
             DDRB &= ~(1 << IRQ_BIT_n);
-            PORTB &= ~(1 << ACT_BIT_n);
+            PORTD &= ~(1 << ACT_BIT_n);
 
             if (dval & (1 << CLK_BIT))
             {
@@ -113,7 +113,7 @@ void start_command()
                     ;
             }
 
-            DDRD = 0xc0;
+            DDRD = 0xc0 | (1 << ACT_BIT_n);
             DDRC = 0x3f;
 
             if (!(PIND & (1 << CP_BIT_n)))
@@ -128,7 +128,7 @@ void start_command()
             else // Slow
                 SPCR = (1 << SPE) | (1 << MSTR) | (1 << SPR1) | (1 << SPR0);
 
-            PORTB &= ~(1 << ACT_BIT_n);
+            PORTD &= ~(1 << ACT_BIT_n);
         }
 
         while (1)
@@ -139,7 +139,7 @@ do_read:
     SPDR = 0xff;
 
     PORTD = (dval & 0xc0) | (1 << CP_BIT_n) | (1 << REQ_BIT_n);
-    DDRD = 0xc0;
+    DDRD = 0xc0 | (1 << ACT_BIT_n);
 
     PORTC = cval;
     DDRC = 0x3f;
@@ -221,10 +221,8 @@ ISR(INT0_vect, ISR_NAKED)
 
     if (PIND & (1 << REQ_BIT_n))
     {
-        PORTB |= (1 << ACT_BIT_n);
-
-        DDRD = 0;
-        PORTD = (1 << CP_BIT_n) | (1 << REQ_BIT_n);
+        DDRD = (1 << ACT_BIT_n);
+        PORTD = (1 << ACT_BIT_n) | (1 << CP_BIT_n) | (1 << REQ_BIT_n);
 
         DDRC = 0;
         PORTC = 0;
@@ -259,15 +257,15 @@ ISR(INT1_vect, ISR_NAKED)
 
 void main()
 {
-    DDRB = (1 << SCK_BIT) | (1 << MOSI_BIT) | (1 << SS_BIT_n) | (1 << ACT_BIT_n);
-    PORTB = (1 << SS_BIT_n) | (1 << ACT_BIT_n);
+    DDRB = (1 << SCK_BIT) | (1 << MOSI_BIT) | (1 << SS_BIT_n);
+    PORTB = (1 << SS_BIT_n);
 
     // SPI enabled, master, fosc/64 = 250 kHz
     SPCR = (1 << SPE) | (1 << MSTR) | (1 << SPR1) | (1 << SPR0);
     SPSR |= (1 << SPI2X);
 
-    DDRD = 0;
-    PORTD = (1 << CP_BIT_n) | (1 << REQ_BIT_n);
+    DDRD = (1 << ACT_BIT_n);
+    PORTD =  (1 << ACT_BIT_n) | (1 << CP_BIT_n) | (1 << REQ_BIT_n);
 
     DDRC = 0;
     PORTC = 0;
diff --git a/hardware/assembly-instructions.md b/hardware/assembly-instructions.md
index d97e750..4467de6 100644
--- a/hardware/assembly-instructions.md
+++ b/hardware/assembly-instructions.md
@@ -15,8 +15,8 @@ Connect the parallel port to the Nano as follows:
 |  8 |   D6 |  D6 | PD6 |
 |  9 |   D7 |  D7 | PD7 |
 | 10 |  ACK |  D9 | PB1 |
-| 11 | BUSY |  D8 | PB0 |
-| 12 | POUT |  D4 | PD4 |
+| 11 | BUSY |  D4 | PD4 |
+| 12 | POUT |  D5 | PD5 |
 | 13 |  SEL |  D2 | PD2 |
 | 18..25 |  GND | GND | GND |