From 6275379e68eb45eb5b6a1b28d83edf45b39f8abc Mon Sep 17 00:00:00 2001 From: asterix Date: Thu, 30 Sep 2010 10:29:29 +0000 Subject: [PATCH] Add comment. git-svn-id: https://src.develer.com/svnoss/bertos/trunk@4376 38d2e660-2303-0410-9eaa-f027e97ec537 --- bertos/algo/crc.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/bertos/algo/crc.c b/bertos/algo/crc.c index c7444740..d4293f9e 100644 --- a/bertos/algo/crc.c +++ b/bertos/algo/crc.c @@ -38,8 +38,14 @@ #include "crc.h" -/** - * crctab calculated by Mark G. Mendel, Network Systems Corporation +/* + * The boot on AVR cpu is placed at the end of flash memory, but the avr + * address memory by byte and the pointers are 16bits long, so we are able + * to address 64Kbyte memory max. For this reason we can't read the crctab + * from flash, because it is placed at the end of memory. This is true every + * time we have an AVR cpu with more that 64Kbyte of flash. To fix this problem + * we let the compiler copy the table in RAM at startup. Obviously this solution + * is not efficent, but for now this is the only way. */ #if CPU_HARVARD && !(defined(ARCH_BOOT) && (ARCH & ARCH_BOOT)) #define CRC_TABLE const uint16_t PROGMEM crc16tab[256] @@ -47,6 +53,9 @@ #define CRC_TABLE const uint16_t crc16tab[256] #endif +/** + * crctab calculated by Mark G. Mendel, Network Systems Corporation + */ CRC_TABLE = { 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, -- 2.25.1