From: Michal Sojka <sojkam1@fel.cvut.cz>
Date: Wed, 6 Nov 2013 17:32:50 +0000 (+0100)
Subject: Add comments about CAN frame layout in bitmap
X-Git-Tag: fix-allnoconfig~126
X-Git-Url: http://rtime.felk.cvut.cz/gitweb/can-benchmark.git/commitdiff_plain/a302d8ec061482b2bd5ad61a9e07ee4feb9aa0fa

Add comments about CAN frame layout in bitmap

This revealed that for EFF frames, the calculation is broken. This needs
to be fixed.
---

diff --git a/latester/latester.c b/latester/latester.c
index a5a7c47..e19064a 100644
--- a/latester/latester.c
+++ b/latester/latester.c
@@ -1,6 +1,6 @@
 /**************************************************************************/
 /* CAN latency tester                                                     */
-/* Copyright (C) 2010, 2011, 2012 Michal Sojka, DCE FEE CTU Prague        */
+/* Copyright (C) 2010, 2011, 2012, 2013 Michal Sojka, DCE FEE CTU Prague  */
 /* License: GPLv2     	     	    	    				  */
 /**************************************************************************/
 
@@ -237,6 +237,11 @@ unsigned calc_stuff_bits(struct can_frame *frame) {
 /* 	printf("Frame: %s\n", received); */
 	
 	if (frame->can_id & CAN_EFF_FLAG) {
+		// bit 31                              0
+		// [0] |...........................sBBBB| s = SOF, B = Base ID (11 bits)
+		// [1] |BBBBBBBSIEEEEEEEEEEEEEEEEEER10DLC4| S = SRR, I = IDE, E = Extended ID (18 bits), DLC4 = DLC
+		// [2] |00000000111111112222222233333333| Data bytes, MSB first
+		// [3] |44444444555555556666666677777777|
 		bitmap[0] =
 			((frame->can_id & CAN_EFF_MASK) >> 25);
 		bitmap[1] =
@@ -251,6 +256,10 @@ unsigned calc_stuff_bits(struct can_frame *frame) {
 		start = 27;
 		end = 64 + 8*frame->can_dlc;
 	} else {
+		// bit 31                              0
+		// [0] |.............sIIIIIIIIIIIRE0DLC4| s = SOF, I = ID (11 bits), R = RTR, E = IDE, DLC4 = DLC
+		// [1] |00000000111111112222222233333333| Data bytes, MSB first
+		// [2] |44444444555555556666666677777777|
 		bitmap[0] =
 			(frame->can_id << 7) |
 			(!!(frame->can_id & CAN_RTR_FLAG)) << 6 |