From 18bb15bec664229016cd45971e0b421ff296a840 Mon Sep 17 00:00:00 2001
From: Tom Nisbet <t.talk@nisbethome.com>
Date: Fri, 3 May 2024 23:04:59 -0400
Subject: [PATCH] update 27_CE algorithm for overwrite pulses

---
 TommyPROM/PromDevice27.cpp            | 21 ++++++++++++++++-----
 TommyPROM/PromDevice27.h              |  2 +-
 TommyPROM/TommyPROM.ino               | 23 ++++++++++++++++++++++-
 docs/_docs/ref-900-release-history.md |  1 +
 4 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/TommyPROM/PromDevice27.cpp b/TommyPROM/PromDevice27.cpp
index ae10394..0125e22 100644
--- a/TommyPROM/PromDevice27.cpp
+++ b/TommyPROM/PromDevice27.cpp
@@ -130,7 +130,7 @@ bool PromDevice27::burnByteWE(byte value, uint32_t address)
         writeDataBus(value);
         delayMicroseconds(1);
         enableWrite();
-        myDelay(mPulseWidthUsec * mOverwriteMultiplier);
+        myDelay(mPulseWidthUsec * mOverwriteMultiplier * (writeCount + 1));
         disableWrite();
     }
 
@@ -179,7 +179,18 @@ bool PromDevice27::burnByteCE(byte value, uint32_t address)
 	        enableOutput();
 	        status = readDataBus() == value;
 	        disableOutput();
-		}
+		} else {
+            status = true;
+        }
+    }
+
+    if (status && (mOverwriteMultiplier > 0)) {
+        setDataBusMode(OUTPUT);
+        writeDataBus(value);
+        delayMicroseconds(1);
+        enableChip();
+        myDelay(mPulseWidthUsec * mOverwriteMultiplier * (writeCount + 1));
+        disableChip();
     }
 
 	setDataBusMode(INPUT);
@@ -244,15 +255,15 @@ ERET PromDevice27::erase(uint32_t start, uint32_t end)
 }
 
 
-void PromDevice27::myDelay(unsigned int us)
+void PromDevice27::myDelay(uint32_t us)
 {
     if (us > 16000) {
         // The delayMicroseconds code can't do delays longer than 16ms, so use the
         // ms delay code for larger values.  This rounds down to the nearest ms, so
         // it is not possible to delay for 40.5 ms, for example.
-        delay(us / 1000);
+        delay(uint16_t(us / 1000));
     } else {
-        delayMicroseconds((unsigned int) us);
+        delayMicroseconds(uint16_t(us));
     }
 }
 
diff --git a/TommyPROM/PromDevice27.h b/TommyPROM/PromDevice27.h
index 7421390..7a439be 100644
--- a/TommyPROM/PromDevice27.h
+++ b/TommyPROM/PromDevice27.h
@@ -50,7 +50,7 @@ class PromDevice27 : public PromDevice
 
     bool burnByteWE(byte value, uint32_t address);
     bool burnByteCE(byte value, uint32_t address);
-    void myDelay(unsigned int us);
+    void myDelay(uint32_t us);
 
     E27C_PGM mPgmType;
     unsigned long mPulseWidthUsec;
diff --git a/TommyPROM/TommyPROM.ino b/TommyPROM/TommyPROM.ino
index 5507550..84169af 100644
--- a/TommyPROM/TommyPROM.ino
+++ b/TommyPROM/TommyPROM.ino
@@ -19,7 +19,7 @@
 #include "XModem.h"
 
 
-static const char * MY_VERSION = "3.6";
+static const char * MY_VERSION = "3.7";
 
 
 // Global status
@@ -49,6 +49,7 @@ PromDevice28C  prom(32 * 1024L, 64, 10, true);
 //PromDevice27  prom(8 * 1024L, E27C_PGM_WE, 1000L, 15, 4);  // 2764 with SEEQ intelligent programming
 //PromDevice27  prom(32 * 1024L, E27C_PGM_WE, 1000L, 25, 3); // 27C256 with SEEQ intelligent programming
 PromDevice27  prom(32 * 1024L, E27C_PGM_CE, 100L, 25, 0); // M27C256 with Presto II intelligent programming
+//PromDevice27  prom(32 * 1024L, E27C_PGM_CE, 1000L, 25, 3); // M27256 with fast programming
 //PromDevice27  prom(2 * 1024L, E27C_PGM_WE, 50000L, 1, 0);  // 2716 with single 50ms write
 //PromDevice27  prom(512 * 1024L, E27C_PGM_CE, 100L, 11, 0); // 27C040 with Atmel rapid programming, CE connected to CE#/PGM#
 //PromDevice27  prom(32 * 1024L, E27C_PGM_CE, 100L, 25, 0);  // W27C257/W27E257 with 100uS program pulse on CE
@@ -337,6 +338,7 @@ bool checkForBreak()
 word checksumBlock(uint32_t start, uint32_t end)
 {
     word checksum = 0;
+#if 1
     for (uint32_t addr = start; (addr <= end); addr += 2)
     {
         word w = prom.readData(addr);
@@ -344,6 +346,25 @@ word checksumBlock(uint32_t start, uint32_t end)
         w |= prom.readData(addr + 1);
         checksum += w;
     }
+#else
+    uint16_t crc = 0xffff;
+    for (uint32_t addr = start; (addr <= end); addr++)
+    {
+        crc = crc ^ (uint16_t(prom.readData(addr)) << 8);
+        for (int ix = 0; (ix < 8); ix++)
+        {
+            if (crc & 0x8000)
+            {
+                crc = (crc << 1) ^ 0x1021;
+            }
+            else
+            {
+                crc <<= 1;
+            }
+        }
+    }
+    checksum = crc;
+#endif
 
     return checksum;
 }
diff --git a/docs/_docs/ref-900-release-history.md b/docs/_docs/ref-900-release-history.md
index e64a148..617a7dc 100644
--- a/docs/_docs/ref-900-release-history.md
+++ b/docs/_docs/ref-900-release-history.md
@@ -30,3 +30,4 @@ exerpt: "What's New in TommyPROM"
 |3.4      |2024-04-09 |Support 2316,2332, and 2364 mask-programmed ROMs|
 |3.5      |2024-04-12 |jcranes's updates to CLI for better parameter defaults and additional error checking|
 |3.6      |2024-04-23 |Remove debug commands by default - can be enabled in Configure.h|
+|3.7      |2024-05-03 |Change overwrite algorithm for 27 series to match SEEQ and M27256 datasheets|