From 0416a2f53688fc41d3a3321445d526a960804b3b Mon Sep 17 00:00:00 2001
From: Olaf Rempel <razzor@kopf-tisch.de>
Date: Sat, 1 Feb 2020 22:45:26 +0100
Subject: [PATCH] Cleanup and reduce size

---
 README.md | 13 +++++++------
 main.c    | 46 +++++++++++++++++++++-------------------------
 2 files changed, 28 insertions(+), 31 deletions(-)

diff --git a/README.md b/README.md
index 207fd99..ec12bbb 100644
--- a/README.md
+++ b/README.md
@@ -3,17 +3,17 @@ twiboot is a simple/small bootloader for AVR MCUs with integrated TWI peripheral
 It was originally created to update I2C controlled BLMCs (Brushless Motor Controller) without an AVR ISP adapter.
 
 twiboot acts as a slave device on a TWI/I2C bus and allows reading/writing of the internal flash memory.
-As a compile time option twiboot also allows reading/writing of the whole internal EEPROM memory.
+As a compile time option (EEPROM_SUPPORT) twiboot also allows reading/writing of the whole internal EEPROM memory.
 The bootloader is not able to update itself (only application flash memory region accessible).
 
 Currently the following AVR MCUs are supported:
 
 AVR MCU | Flash bytes used (.text + .data) | Bootloader region size
 --- | --- | ---
-atmega8 | 724 (0x2D4) | 512 words
-atmega88 | 744 (0x2E8) | 512 words
-atmega168 | 744 (0x2E8) | 512 words
-atmega328p | 744 (0x2E8) | 512 words
+atmega8 | 706 (0x2C2) | 512 words
+atmega88 | 726 (0x2D6) | 512 words
+atmega168 | 726 (0x2D6) | 512 words
+atmega328p | 726 (0x2D6) | 512 words
 
 (Compiled on Ubuntu 18.04 LTS (gcc 5.4.0 / avr-libc 2.0.0) with EEPROM and LED support)
 
@@ -33,7 +33,7 @@ A TWI/I2C master can use the protocol to
 - write the internal eeprom (byte wise)
 - exit the bootloader and start the application
 
-As a compile time option twiboot can output its state with two LEDs.
+As a compile time option (LED_SUPPORT) twiboot can output its state with two LEDs.
 One LED will flash with a frequency of 20Hz while twiboot is active (including boot wait time).
 A second LED will flash when the bootloader is addressed on the TWI/I2C bus.
 
@@ -85,6 +85,7 @@ Write 1+ eeprom bytes | **SLA+W**, 0x02, 0x02, addrh, addrl, {* bytes}, **STO**
 The multiboot_tool repository contains a simple linux application that uses
 this protocol to access the bootloader over linux i2c device.
 
+The ispprog programming adapter can also be used as a avr910/butterfly to twiboot protocol bridge.
 
 ## Development ##
 Issue reports, feature requests, patches or simply success stories are much appreciated.
diff --git a/main.c b/main.c
index 48e42c4..0859d5f 100644
--- a/main.c
+++ b/main.c
@@ -141,26 +141,24 @@ static void write_flash_page(void)
     uint8_t size = SPM_PAGESIZE;
     uint8_t *p = buf;
 
-    if (pagestart >= BOOTLOADER_START)
+    if (pagestart < BOOTLOADER_START)
     {
-        return;
+        boot_page_erase(pagestart);
+        boot_spm_busy_wait();
+
+        do {
+            uint16_t data = *p++;
+            data |= *p++ << 8;
+            boot_page_fill(addr, data);
+
+            addr += 2;
+            size -= 2;
+        } while (size);
+
+        boot_page_write(pagestart);
+        boot_spm_busy_wait();
+        boot_rww_enable();
     }
-
-    boot_page_erase(pagestart);
-    boot_spm_busy_wait();
-
-    do {
-        uint16_t data = *p++;
-        data |= *p++ << 8;
-        boot_page_fill(addr, data);
-
-        addr += 2;
-        size -= 2;
-    } while (size);
-
-    boot_page_write(pagestart);
-    boot_spm_busy_wait();
-    boot_rww_enable();
 } /* write_flash_page */
 
 
@@ -168,12 +166,11 @@ static void write_flash_page(void)
 /* *************************************************************************
  * read_eeprom_byte
  * ************************************************************************* */
-static uint8_t read_eeprom_byte(void)
+static uint8_t read_eeprom_byte(uint16_t address)
 {
-    EEARL = addr;
-    EEARH = (addr >> 8);
+    EEARL = address;
+    EEARH = (address >> 8);
     EECR |= (1<<EERE);
-    addr++;
 
     return EEDR;
 } /* read_eeprom_byte */
@@ -223,6 +220,7 @@ static uint8_t TWI_data_write(uint8_t bcnt, uint8_t data)
                 case CMD_WAIT:
                     /* abort countdown */
                     boot_timeout = 0;
+                    cmd = data;
                     break;
 
                 default:
@@ -231,8 +229,6 @@ static uint8_t TWI_data_write(uint8_t bcnt, uint8_t data)
                     ack = 0x00;
                     break;
             }
-
-            cmd = data;
             break;
 
         case 1:
@@ -334,7 +330,7 @@ static uint8_t TWI_data_read(uint8_t bcnt)
 
 #if (EEPROM_SUPPORT)
         case CMD_ACCESS_EEPROM:
-            data = read_eeprom_byte();
+            data = read_eeprom_byte(addr++);
             break;
 #endif /* (EEPROM_SUPPORT) */