From 6d9a958907f6ce6889ba4d46aa1d33d94919709e Mon Sep 17 00:00:00 2001
From: Tom Nisbet <t.talk@nisbethome.com>
Date: Sun, 11 Oct 2020 23:16:15 -0400
Subject: [PATCH] Add 74LS595 code to the HardwareVerify sketch

---
 HardwareVerify/PromAddressDriver.cpp | 74 ++++++++++++++--------------
 HardwareVerify/PromAddressDriver.h   |  2 -
 2 files changed, 36 insertions(+), 40 deletions(-)

diff --git a/HardwareVerify/PromAddressDriver.cpp b/HardwareVerify/PromAddressDriver.cpp
index 4ba70c6..c350159 100644
--- a/HardwareVerify/PromAddressDriver.cpp
+++ b/HardwareVerify/PromAddressDriver.cpp
@@ -1,9 +1,28 @@
+// This controls the shift register that generates the address lines for A0..A15 for most
+// chip families.
+//
+// Note that this uses direct port control instead of digitalWrite calls so that the code
+// can run fast enough to meet the tBLC requirements for SDP and block writes.  This
+// sacrifices portability and readability for speed. 
+//
+// This code will only work on Arduino Uno and Nano hardware.  The ports for other
+// Arduinos map to different IO pins.
+
 #include "PromAddressDriver.h"
 
 #define ADDR_CLK_HI     A3
 #define ADDR_CLK_LO     A4
 #define ADDR_DATA       A5
 
+// Define masks for the address clk and data lines on PC3..PC5 for direct port control.
+#define ADDR_CLK_HI_MASK    0x08
+#define ADDR_CLK_LO_MASK    0x10
+#define ADDR_DATA_MASK      0x20
+
+// When using the 74LS595 shift registers, the RCLK lines of both shift registers can be
+// connected to D13 (PB5).
+#define RCLK_595_MASK       0x20
+
 
 void PromAddressDriver::begin()
 {
@@ -14,7 +33,7 @@ void PromAddressDriver::begin()
     digitalWrite(ADDR_DATA, LOW);
     digitalWrite(ADDR_CLK_LO, LOW);
     digitalWrite(ADDR_CLK_HI, LOW);
-
+    DDRB |= RCLK_595_MASK; // Set D13 as output
 
     // To save time, the setAddress only writes the hi byte if it has changed.
     // The value used to detect the change is initialized to a non-zero value,
@@ -33,50 +52,22 @@ void PromAddressDriver::setAddress(word address)
 
     if (hi != lastHi)
     {
-        setAddressRegisterDirect(ADDR_CLK_HI, hi);
+        setAddressRegister(ADDR_CLK_HI, hi);
         lastHi = hi;
     }
-    setAddressRegisterDirect(ADDR_CLK_LO, lo);
+    setAddressRegister(ADDR_CLK_LO, lo);
 }
 
-
 // Shift an 8-bit value into one of the address shift registers.  Note that
 // the data pins are tied together, selecting the high or low address register
 // is a matter of using the correct clock pin to shift the data in.
 void PromAddressDriver::setAddressRegister(uint8_t clkPin, byte addr)
-{
-    // Make sure the clock is low to start.
-    digitalWrite(clkPin, LOW);
-
-    // Shift 8 bits in, starting with the MSB.
-    for (int ix = 0; (ix < 8); ix++)
-    {
-        // Set the data bit
-        if (addr & 0x80)
-        {
-            digitalWrite(ADDR_DATA, HIGH);
-        }
-        else
-        {
-            digitalWrite(ADDR_DATA, LOW);
-        }
-
-        digitalWrite(clkPin, HIGH); // Clock in a bit
-        digitalWrite(clkPin, LOW);  // Reset the clock pin
-        addr <<= 1;
-    }
-}
-
-// Shift an 8-bit value into one of the address shift registers.  Note that
-// the data pins are tied together, selecting the high or low address register
-// is a matter of using the correct clock pin to shift the data in.
-void PromAddressDriver::setAddressRegisterDirect(uint8_t clkPin, byte addr)
 {
     byte mask = 0;
-    if (clkPin == A3)
-        mask = 0x08;
-    else if (clkPin == A4)
-        mask = 0x10;
+    if (clkPin == ADDR_CLK_HI)
+        mask = ADDR_CLK_HI_MASK;
+    else if (clkPin == ADDR_CLK_LO)
+        mask = ADDR_CLK_LO_MASK;
 
     // Make sure the clock is low to start.
     PORTC &= ~mask;
@@ -87,11 +78,11 @@ void PromAddressDriver::setAddressRegisterDirect(uint8_t clkPin, byte addr)
         // Set the data bit
         if (addr & 0x80)
         {
-            PORTC |= 0x20;
+            PORTC |= ADDR_DATA_MASK;
         }
         else
         {
-            PORTC &= 0xdf;
+            PORTC &= ~ADDR_DATA_MASK;
         }
 
         // Toggle the clock high then low
@@ -100,5 +91,12 @@ void PromAddressDriver::setAddressRegisterDirect(uint8_t clkPin, byte addr)
         PORTC &= ~mask;
         addr <<= 1;
     }
-}
 
+    // Toggle the output latch for 74LS595 hardware.  For the default TommyPROM hardware
+    // this just harmlessly writes to the D13 line that isn't connected to anything.
+    PORTB &= ~RCLK_595_MASK;
+    delayMicroseconds(1);
+    PORTB |= RCLK_595_MASK;
+    delayMicroseconds(1);
+    PORTB &= ~RCLK_595_MASK;
+}
diff --git a/HardwareVerify/PromAddressDriver.h b/HardwareVerify/PromAddressDriver.h
index 89ec740..900ec91 100644
--- a/HardwareVerify/PromAddressDriver.h
+++ b/HardwareVerify/PromAddressDriver.h
@@ -10,9 +10,7 @@ class PromAddressDriver {
 
   private:
     static void setAddressRegister(uint8_t clkPin, byte addr);
-    static void setAddressRegisterDirect(uint8_t clkPin, byte addr);
 };
 
 
 #endif // #define INCLUDE_PROM_ADDRESS_DRIVER_H
-