>From 1b3a2fe3b3257ddb198507b2c87dbcb80735dc3d Mon Sep 17 00:00:00 2001
From: Dirk Hohndel <dirk@hohndel.org>
Date: Wed, 24 Sep 2014 21:26:32 -0700
Subject: [PATCH 2/5] Prepare Oceanic infrastructure for multi page reads

Some new Oceanic dive computers like the Aeris A300CS support a new read
command that always reads 256 byte pages instead of 16 byte pages, other
versions support reading 128 byte pages.

This patch adds a field to the oceanic_atom2_device_t structure to
indicate which type of device this is. The multipage algorithm will
request larger, aligned reads wherever possible and fall back to standard
16 byte reads otherwise.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
---
 src/oceanic_atom2.c | 58 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 45 insertions(+), 13 deletions(-)

diff --git a/src/oceanic_atom2.c b/src/oceanic_atom2.c
index 17e19580d42f..9fd10f56a90d 100644
--- a/src/oceanic_atom2.c
+++ b/src/oceanic_atom2.c
@@ -49,6 +49,8 @@ typedef struct oceanic_atom2_device_t {
 	oceanic_common_device_t base;
 	serial_t *port;
 	unsigned int delay;
+	unsigned char bigpage;
+
 } oceanic_atom2_device_t;
 
 static dc_status_t oceanic_atom2_device_read (dc_device_t *abstract, unsigned int address, unsigned char data[], unsigned int size);
@@ -406,9 +408,15 @@ oceanic_atom2_transfer (oceanic_atom2_device_t *device, const unsigned char comm
 			return EXITCODE (n);
 		}
 
-		// Verify the checksum of the answer.
-		unsigned char crc = answer[asize - 1];
-		unsigned char ccrc = checksum_add_uint8 (answer, asize - 1, 0x00);
+		// Verify the checksum of the answer; we can use unsigned short in both cases
+		unsigned short crc, ccrc;
+		if (asize == 256 + 2) { // 256 byte pages get two crc bytes
+			crc = (answer[asize - 1] << 8) | answer[asize - 2] ;
+			ccrc = checksum_add_uint16 (answer, asize - 2, 0x0000);
+		} else {
+			crc = answer[asize - 1];
+			ccrc = checksum_add_uint8 (answer, asize - 1, 0x00);
+		}
 		if (crc != ccrc) {
 			ERROR (abstract->context, "Unexpected answer checksum.");
 			return DC_STATUS_PROTOCOL;
@@ -451,6 +459,7 @@ oceanic_atom2_device_open (dc_device_t **out, dc_context_t *context, const char
 	// Set the default values.
 	device->port = NULL;
 	device->delay = 0;
+	device->bigpage = 1; // no big pages
 
 	// Open the device.
 	int rc = serial_open (&device->port, context, name);
@@ -598,33 +607,56 @@ oceanic_atom2_device_version (dc_device_t *abstract, unsigned char data[], unsig
 }
 
 
+/* if we have aligned reads of a larger pagesize (and the device supports that), use the larger
+ * block reads, otherwise just loop and read in PAGESIZE chunks */
 static dc_status_t
 oceanic_atom2_device_read (dc_device_t *abstract, unsigned int address, unsigned char data[], unsigned int size)
 {
 	oceanic_atom2_device_t *device = (oceanic_atom2_device_t*) abstract;
 
-	if ((address % PAGESIZE != 0) ||
-		(size    % PAGESIZE != 0))
+	// pick the best pagesize to use
+	unsigned int pagesize = PAGESIZE;
+
+	if (size == device->bigpage * PAGESIZE && address % (device->bigpage * PAGESIZE) == 0)
+		pagesize = device->bigpage * PAGESIZE;
+
+	// pick the correct read command and number of crc bytes based on the page size
+	unsigned char read_cmd, crc_size;
+	if (pagesize == 256) {
+		read_cmd = 0xB8;
+		crc_size = 2;
+	} else if (pagesize == 128) {
+		read_cmd = 0xB4;
+		crc_size = 1;
+	} else {
+		read_cmd = 0xB1;
+		crc_size = 1;
+	}
+
+	if ((address % pagesize != 0) ||
+	    (size    % pagesize != 0))
 		return DC_STATUS_INVALIDARGS;
 
 	unsigned int nbytes = 0;
+
 	while (nbytes < size) {
 		// Read the package.
-		unsigned int number = address / PAGESIZE;
-		unsigned char answer[PAGESIZE + 1] = {0};
-		unsigned char command[4] = {0xB1,
+		unsigned int number = address / PAGESIZE;      // this is always PAGESIZE, even in BIGPAGE mode
+		unsigned char answer[256 + 2] = {0};           // maximum we support for the known commands
+		unsigned int answersize = pagesize + crc_size;
+		unsigned char command[4] = {read_cmd,
 				(number >> 8) & 0xFF, // high
 				(number     ) & 0xFF, // low
 				0};
-		dc_status_t rc = oceanic_atom2_transfer (device, command, sizeof (command), answer, sizeof (answer));
+		dc_status_t rc = oceanic_atom2_transfer (device, command, sizeof (command), answer, answersize);
 		if (rc != DC_STATUS_SUCCESS)
 			return rc;
 
-		memcpy (data, answer, PAGESIZE);
+		memcpy (data, answer, pagesize);
 
-		nbytes += PAGESIZE;
-		address += PAGESIZE;
-		data += PAGESIZE;
+		nbytes += pagesize;
+		address += pagesize;
+		data += pagesize;
 	}
 
 	return DC_STATUS_SUCCESS;
-- 
1.8.0.rc0.18.gf84667d