From b9ea7fa7866263596f5fcf93c6c2c1a778554d62 Mon Sep 17 00:00:00 2001
From: Jared Boone <jboone@earfeast.com>
Date: Mon, 7 Dec 2015 11:38:35 -0800
Subject: [PATCH] ERT CRC checking for SCM packets.

IDM coming as soon as I can address packet truncation...
---
 firmware/application/app_ert.cpp | 17 +++++++++++++++++
 firmware/application/app_ert.hpp |  2 ++
 2 files changed, 19 insertions(+)

diff --git a/firmware/application/app_ert.cpp b/firmware/application/app_ert.cpp
index a6cbde5e4..6a08888a3 100644
--- a/firmware/application/app_ert.cpp
+++ b/firmware/application/app_ert.cpp
@@ -29,6 +29,7 @@ using namespace portapack;
 #include "lpc43xx_cpp.hpp"
 using namespace lpc43xx;
 
+#include "crc.hpp"
 #include "string_format.hpp"
 
 namespace ert {
@@ -71,6 +72,21 @@ Consumption Packet::consumption() const {
 	return invalid_consumption;
 }
 
+bool Packet::crc_ok() const {
+	if( type() == ERTPacket::Type::SCM ) {
+		CRC<uint16_t> ert_bch { 0x6f63 };
+		size_t start_bit = 5;
+		auto crc_calculated = ert_bch.calculate_byte(0x0000, reader_.read(0, start_bit));
+		for(size_t i=start_bit; i<length(); i+=8) {
+			const uint8_t byte = reader_.read(i, 8);
+			crc_calculated = ert_bch.calculate_byte(crc_calculated, byte);
+		}
+		return crc_calculated == 0x0000;
+	}
+
+	return false;
+}
+
 } /* namespace ert */
 
 ERTModel::ERTModel() {
@@ -122,6 +138,7 @@ void ERTView::on_packet(const ert::Packet& packet) {
 		msg += to_string_dec_uint(packet.id(), 10);
 		msg += " ";
 		msg += to_string_dec_uint(packet.consumption(), 10);
+		msg += packet.crc_ok() ? " *" : " x";
 		break;
 
 	case ERTPacket::Type::IDM:
diff --git a/firmware/application/app_ert.hpp b/firmware/application/app_ert.hpp
index 53b0e533e..8c0880cb2 100644
--- a/firmware/application/app_ert.hpp
+++ b/firmware/application/app_ert.hpp
@@ -72,6 +72,8 @@ public:
 	ID id() const;
 	Consumption consumption() const;
 
+	bool crc_ok() const;
+
 private:
 	using Reader = FieldReader<ManchesterDecoder, BitRemap>;