On Mon, Mar 29, 2010 at 6:36 PM, Luis R. Rodriguez
<[email protected]> wrote:
> On Mon, Mar 29, 2010 at 03:58:37AM -0700, selvam wrote:
>> Hi all,
>> I have some queries in ath9k.
>>
>> In xmit.c, the variable 'bits_per_symbol' is used to store the number of
>> bits per OFDM symbol for various data rates.
>>
>> static u32 bits_per_symbol[][2] = {
>> /* 20MHz 40MHz */
>> { 26, 54 }, /* 0: BPSK */
>> { 52, 108 }, /* 1: QPSK 1/2 */
>> { 78, 162 }, /* 2: QPSK 3/4 */
>> { 104, 216 }, /* 3: 16-QAM 1/2 */
>> { 156, 324 }, /* 4: 16-QAM 3/4 */
>> { 208, 432 }, /* 5: 64-QAM 2/3 */
>> { 234, 486 }, /* 6: 64-QAM 3/4 */
>> { 260, 540 }, /* 7: 64-QAM 5/6 */
>> { 52, 108 }, /* 8: BPSK */
>> { 104, 216 }, /* 9: QPSK 1/2 */
>> { 156, 324 }, /* 10: QPSK 3/4 */
>> { 208, 432 }, /* 11: 16-QAM 1/2 */
>> { 312, 648 }, /* 12: 16-QAM 3/4 */
>> { 416, 864 }, /* 13: 64-QAM 2/3 */
>> { 468, 972 }, /* 14: 64-QAM 3/4 */
>> { 520, 1080 }, /* 15: 64-QAM 5/6 */
>>
>>
>> 1) Is it possible to keep only the values of MCS 0 to MCS 7 and calculate
>> the rest on run time. so that we can save some amount of memory.
>>
>> For example, if MCS index is 8, then multiply the MCS 0 by 2, for MCS 9
>> mutiply MCS 1 by 2..
>>
>> Can we use in that way?. Is there any performance tradeoff in terms of
>> faster execution due to comparison?
>>
>>
>> 2) Why don't we use static u16 instead of static u32 to declare this
>> variable? Is there any specific reason for using as u32?
>>
>> If my approach is improper, please excuse me.
>
> Try the patch and send it once tested and proved to work :)
>
> Luis
> _______________________________________________
> ath9k-devel mailing list
> [email protected]
> https://lists.ath9k.org/mailman/listinfo/ath9k-devel
>
The following patch works for me:
Index: linux-2.6.33.1/drivers/net/wireless/ath/ath9k/xmit.c
===================================================================
--- linux-2.6.33.1.orig/drivers/net/wireless/ath/ath9k/xmit.c 2010-03-30
01:24:25.906770962 +0200
+++ linux-2.6.33.1/drivers/net/wireless/ath/ath9k/xmit.c 2010-03-30
01:29:11.602996328 +0200
@@ -33,7 +33,7 @@
#define OFDM_SIFS_TIME 16
-static u32 bits_per_symbol[][2] = {
+static u16 bits_per_symbol[][2] = {
/* 20MHz 40MHz */
{ 26, 54 }, /* 0: BPSK */
{ 52, 108 }, /* 1: QPSK 1/2 */
@@ -43,14 +43,6 @@
{ 208, 432 }, /* 5: 64-QAM 2/3 */
{ 234, 486 }, /* 6: 64-QAM 3/4 */
{ 260, 540 }, /* 7: 64-QAM 5/6 */
- { 52, 108 }, /* 8: BPSK */
- { 104, 216 }, /* 9: QPSK 1/2 */
- { 156, 324 }, /* 10: QPSK 3/4 */
- { 208, 432 }, /* 11: 16-QAM 1/2 */
- { 312, 648 }, /* 12: 16-QAM 3/4 */
- { 416, 864 }, /* 13: 64-QAM 2/3 */
- { 468, 972 }, /* 14: 64-QAM 3/4 */
- { 520, 1080 }, /* 15: 64-QAM 5/6 */
};
#define IS_HT_RATE(_rate) ((_rate) & 0x80)
@@ -598,7 +590,7 @@
if (nsymbols == 0)
nsymbols = 1;
- nsymbits = bits_per_symbol[rix][width];
+ nsymbits = bits_per_symbol[rix & 3][width] * ((rix >> 3) + 1);
minlen = (nsymbols * nsymbits) / BITS_PER_BYTE;
if (frmlen < minlen) {
@@ -1452,7 +1444,7 @@
/* find number of symbols: PLCP + data */
nbits = (pktlen << 3) + OFDM_PLCP_BITS;
- nsymbits = bits_per_symbol[rix][width];
+ nsymbits = bits_per_symbol[rix & 3][width] * ((rix >> 3) + 1);
nsymbols = (nbits + nsymbits - 1) / nsymbits;
if (!half_gi)
--
Matteo Croce
OpenWrt Developer
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