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As Juergen Heinzl pointed out, much of my original fwi calculations evaluated 

to zero due to the integer range limitations.  shifting everything to the microsecond
range should solve this problem without introducing ugly floating point arithmetics.


git-svn-id: https://svn.gnumonks.org/trunk/librfid@1425 e0336214-984f-0b4b-a45f-81c69e1f0ede
This commit is contained in:
laforge 2005-09-11 19:59:05 +00:00
parent a9d8406846
commit a740a7a578
4 changed files with 39 additions and 8 deletions
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2
include/rfid/rfid_layer2_iso14443b.h
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@ -49,7 +49,7 @@ struct iso14443b_handle {
unsigned int fsc; /* max. frame size card */
unsigned int fsd; /* max. frame size reader */
unsigned int fwt; /* frame waiting time */
unsigned int fwt; /* frame waiting time (in usec) */
unsigned int mbl; /* maximum buffer length */

4
include/rfid/rfid_protocol_tcl.h
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@ -21,9 +21,9 @@ struct tcl_handle {
unsigned int fsc; /* max frame size accepted by card */
unsigned int fsd; /* max frame size accepted by reader */
unsigned int fwt; /* frame waiting time */
unsigned int fwt; /* frame waiting time (in usec)*/
unsigned char ta; /* divisor information */
unsigned char sfgt; /* start-up frame guard time */
unsigned char sfgt; /* start-up frame guard time (in usec) */
/* otherwise determined */
unsigned int cid; /* Card ID */

15
rfid_layer2_iso14443b.c
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@ -36,10 +36,23 @@
static inline int
fwi_to_fwt(struct rfid_layer2_handle *h, unsigned int *fwt, unsigned int fwi)
{
unsigned int multiplier;
/* 15 is RFU */
if (fwi > 14)
return -1;
return (256 * 16 / h->rh->ah->asic->fc) * 2 ^ fwi;
/* According to ISO 14443-3:200(E), Chapter 7.9.4.3, the forumala is
* (256 * 16 / fC) * 2^fwi We avoid floating point computations by
* shifting everything into the microsecond range. In integer
* calculations 1000000*256*16/13560000 evaluates to 302 (instead of
* 302.064897), which provides sufficient precision, IMHO. The max
* result is 302 * 16384 (4947968), which fits well within the 31/32
* bit range of an integer */
multiplier = 1 << fwi; /* 2 to the power of fwi */
return (1000000 * 256 * 16 / h->rh->ah->asic->fc) * multiplier
}
static int

26
rfid_proto_tcl.c
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@ -40,15 +40,33 @@
static unsigned int sfgi_to_sfgt(struct rfid_protocol_handle *h,
unsigned char sfgi)
{
/* ISO 14443-4:2000(E) Section 5.2.5. */
return (256 * 16 / h->l2h->rh->ah->fc) * (2 ^ sfgi);
unsigned int multiplier;
if (sfgi > 14)
sfgi = 14;
multiplier = 1 << sfgi; /* 2 to the power of sfgi */
/* ISO 14443-4:2000(E) Section 5.2.5:
* (256 * 16 / h->l2h->rh->ah->fc) * (2 ^ sfgi) */
return (1000000 * 256*16 / h->l2h->rh->ah->fc) * multiplier;
}
static unsigned int fwi_to_fwt(struct rfid_protocol_handle *h,
unsigned char fwi)
{
/* ISO 14443-4:2000(E) Section 7.2. */
return (256*16 / h->l2h->rh->ah->fc) * (2 ^ fwi);
unsigned int multiplier;
if (fwi > 14)
fwi = 14;
multiplier = 1 << fwi; /* 2 to the power of fwi */
/* ISO 14443-4:2000(E) Section 7.2.:
* (256*16 / h->l2h->rh->ah->fc) * (2 ^ fwi) */
return (1000000 * 256*16 / h->l2h->rh->ah->fc) * multiplier;
}
#define activation_fwt(x) (65536 / x->l2h->rh->ah->fc)