From 470ee2f5c33fb0c0b74a49fd95d9705af4891237 Mon Sep 17 00:00:00 2001
From: Sergiy Dvodnenko <dvodnenkos@gmail.com>
Date: Mon, 18 Aug 2025 13:56:52 +0300
Subject: [PATCH] Saturn: fixes

-fix reverse seek delay
-add CRC calculation for data sectors (cdbtest)
---
 support/saturn/saturn.h      |   1 +
 support/saturn/saturncdd.cpp | 116 ++++++++++++++++-------------------
 2 files changed, 54 insertions(+), 63 deletions(-)

diff --git a/support/saturn/saturn.h b/support/saturn/saturn.h
index 84cfb9e..fd12613 100644
--- a/support/saturn/saturn.h
+++ b/support/saturn/saturn.h
@@ -100,6 +100,7 @@ private:
 	void ReadData(uint8_t *buf);
 	int ReadCDDA(uint8_t *buf, int first);
 	void MakeSecureRingData(uint8_t *buf);
+	uint32_t DataSectorCalcCRC(uint8_t* buf);
 	int DataSectorSend(uint8_t* header, int speed);
 	int AudioSectorSend(int first);
 	int RingDataSend(uint8_t* header, int speed);
diff --git a/support/saturn/saturncdd.cpp b/support/saturn/saturncdd.cpp
index c5d0f0f..8072e44 100644
--- a/support/saturn/saturncdd.cpp
+++ b/support/saturn/saturncdd.cpp
@@ -500,7 +500,7 @@ int satcdd_t::CalcSeekDelay(int lba_old, int lba_new)
 	if (n <= 4) n = 4;
 	else if (n > 30) n = 30;
 
-	if (diff < 0) n += 2;
+	if (diff < 0 && abs(diff) > 8) n += 2;
 
 	return n;
 }
@@ -1001,7 +1001,7 @@ void satcdd_t::Update() {
 		else if (this->toc.tracks[this->track].type)
 		{
 			// CD-ROM Data (Mode 1/2)
-			uint8_t header[4];
+			uint8_t header[16];
 
 #ifdef SATURN_DEBUG
 			//printf("\x1b[32mSaturn: ");
@@ -1010,10 +1010,22 @@ void satcdd_t::Update() {
 #endif // SATURN_DEBUG
 
 			if (this->sectorSize == 2048 || (this->lba - this->toc.tracks[this->track].start) < 0) {
-				header[0] = BCD(msf.m);
-				header[1] = BCD(msf.s);
-				header[2] = BCD(msf.f);
-				header[3] = (uint8_t)this->toc.tracks[this->track].type;
+				header[0] = 0x00;
+				header[1] = 0xFF;
+				header[2] = 0xFF;
+				header[3] = 0xFF;
+				header[4] = 0xFF;
+				header[5] = 0xFF;
+				header[6] = 0xFF;
+				header[7] = 0xFF;
+				header[8] = 0xFF;
+				header[9] = 0xFF;
+				header[10] = 0xFF;
+				header[11] = 0x00;
+				header[12] = BCD(msf.m);
+				header[13] = BCD(msf.s);
+				header[14] = BCD(msf.f);
+				header[15] = 0x01;
 				DataSectorSend(header, this->speed);
 			}
 			else {
@@ -1132,6 +1144,29 @@ void satcdd_t::MakeSecureRingData(uint8_t *buf) {
 	}
 }
 
+uint32_t satcdd_t::DataSectorCalcCRC(uint8_t* buf)
+{
+	static uint32_t crc_tab[256];
+	for (int i = 0; i < 256; i++)
+	{
+		uint32_t c = i;
+
+		for (unsigned j = 0; j < 8; j++)
+			c = (c >> 1) ^ ((c & 0x1) ? 0xD8018001 : 0);
+
+		crc_tab[i] = c;
+	}
+
+	uint32_t crc = 0;
+	for (int i = 0; i < 2064; i++)
+	{
+		crc ^= buf[i];
+		crc = (crc >> 8) ^ crc_tab[crc & 0xFF];
+	}
+
+	return crc;
+}
+
 void satcdd_t::ReadData(uint8_t *buf)
 {
 	int offs = 0; 
@@ -1219,13 +1254,20 @@ int satcdd_t::DataSectorSend(uint8_t* header, int speed)
 
 	uint8_t *shmem_ptr = (uint8_t*)shmem_map(SHMEM_ADDR, 4096 * 4);
 	uint8_t *data_ptr = shmem_ptr + (buf_num_write * 4096);
+
+	ReadData(data_ptr);
 	if (header) {
-		ReadData(data_ptr);
-		memcpy(data_ptr + 12 , header, 4);
-	}
-	else {
-		ReadData(data_ptr);
+		memcpy(data_ptr, header, 16);
 	}
+
+	uint32_t crc = DataSectorCalcCRC(data_ptr);
+	data_ptr[2064] = crc >> 0;
+	data_ptr[2065] = crc >> 8;
+	data_ptr[2066] = crc >> 16;
+	data_ptr[2067] = crc >> 24;
+
+	memset(data_ptr + 2068, 0, 2352-2068);
+
 	int boot = (data_ptr[12] == 0x00 && data_ptr[13] == 0x02 && data_ptr[14] == 0x00 && data_ptr[15] == 0x01);
 	shmem_unmap(shmem_ptr, 4096 * 4);
 
@@ -1289,55 +1331,3 @@ int satcdd_t::AudioSectorSend(int first)
 
 	return 0;
 }
-
-//int satcdd_t::DataSectorSend(uint8_t* header, int speed)
-//{
-//	uint8_t* data_ptr = cd_buf + 2;
-//
-//	if (header) {
-//		ReadData(data_ptr);
-//		memcpy(data_ptr + 12, header, 4);
-//	}
-//	else {
-//		ReadData(data_ptr);
-//	}
-//	cd_buf[0] = cd_buf[1] = (speed == 2 ? 0x01 : 0x00);
-//
-//	if (SendData)
-//		return SendData(cd_buf, 2352 + 2, CD_DATA_IO_INDEX);
-//
-//	return 0;
-//}
-//
-//int satcdd_t::RingDataSend(uint8_t* header, int speed)
-//{
-//	uint8_t* data_ptr = cd_buf + 2;
-//
-//	if (header) {
-//		MakeSecureRingData(data_ptr);
-//		memcpy(data_ptr + 12, header, 12);
-//		memset(data_ptr + 2348, 0, 4);
-//	}
-//	cd_buf[0] = cd_buf[1] = (speed == 2 ? 1 : 0);
-//
-//	if (SendData)
-//		return SendData(cd_buf, 2352 + 2, CD_DATA_IO_INDEX);
-//
-//	return 0;
-//}
-//
-//int satcdd_t::AudioSectorSend(int first)
-//{
-//	int len;
-//	uint8_t* data_ptr = cd_buf + 2;
-//
-//	len = ReadCDDA(data_ptr, first);
-//	cd_buf[0] = cd_buf[1] = 0x02;
-//
-//	if (SendData)
-//		return SendData(cd_buf, len + 2, CD_DATA_IO_INDEX);
-//
-//	return 0;
-//}
-
-