Let FINALIZE_FLASH return the number of pages erased

Author: matthijskooijman

PROTOCOL.md

@@ -482,6 +482,7 @@ should be sent, except with a zero address to start over.
 |-------|-------------------------------
 | 1     | Status: `COMMAND_OK` (0x00)
 | 1     | Length
+| 1     | Erasecount
 | 1     | CRC
 
 | Bytes | Reply format
@@ -491,6 +492,10 @@ should be sent, except with a zero address to start over.
 | 1     | Reason
 | 1     | CRC
 
+The erasecount is the number of pages erased since the last reset, or
+the last succesful `FINALIZE_FLASH` command. This is returned to
+facilitate verification of the "erase only when needed" mechanism.
+
 When flashing fails for any reason, an additional reason byte is
 returned. The meaning of this byte is purely informative and not defined
 by this protocol, it should be looked up in the bootloader.

SelfProgram.cpp

@@ -29,6 +29,7 @@
 // The actual value is set by main(), to avoid the overhead gcc
 // generates for running a "constructor" to set this value
 uint16_t SelfProgram::trampolineStart = 0;
+uint8_t SelfProgram::eraseCount = 0;
 
 void SelfProgram::readFlash(uint16_t address, uint8_t *data, uint8_t len) {
 	for (uint8_t i=0; i < len; i++) {
@@ -81,8 +82,11 @@ uint8_t SelfProgram::writePage(uint16_t address, uint8_t *data, uint8_t len) {
 	if (address % SPM_ERASESIZE == 0) {
 		// If this is the page containing the trampoline, it
 		// will already be erased when writing the first page
-		if (address / SPM_ERASESIZE != trampolineStart / SPM_ERASESIZE)
+		if (address / SPM_ERASESIZE != trampolineStart / SPM_ERASESIZE) {
+			if (eraseCount < 0xff)
+				++eraseCount;
 			boot_page_erase_safe(address);
+		}
 	}
 
 	for (int i=0; i < len; i += 2) {
@@ -118,6 +122,8 @@ void SelfProgram::writeTrampoline(uint16_t instruction) {
 	// other application code. This makes no attempt to preserve the
 	// other code to keep since simple. This should work since we're
 	// writing a new application anyway.
+	if (eraseCount < 0xff)
+		++eraseCount;
 	boot_page_erase_safe(address);
 
 	// Take the reset instruction from the page at offset 0 and 1

SelfProgram.h

@@ -39,6 +39,8 @@ class SelfProgram {
 	// Use a reference to make this an alias to trampolineStart for
 	// readability
 	static constexpr const uint16_t& applicationSize = trampolineStart;
+
+	static uint8_t eraseCount;
 };
 
 #endif /* SELFPROGRAM_H_ */

bootloader.cpp

@@ -222,7 +222,9 @@ cmd_result processCommand(uint8_t cmd, uint8_t *datain, uint8_t len, uint8_t *da
 				dataout[0] = err;
 				return cmd_result(Status::COMMAND_FAILED, 1);
 			} else {
-				return cmd_ok();
+				dataout[0] = SelfProgram::eraseCount;
+				SelfProgram::eraseCount = 0;
+				return cmd_ok(1);
 			}
 		}
 		case Commands::READ_FLASH: