Date: Fri, 19 Nov 1999 14:21:25 +1000 From: George Michaelson <ggm@dstc.edu.au> To: "Kees Verstoep" <versto@cs.vu.nl> Cc: freebsd-atm@FreeBSD.ORG Subject: Re: Bandwidth Capping fore ATM circuits? Message-ID: <6046.942985285@dstc.edu.au> In-Reply-To: Your message of "Wed, 17 Nov 1999 10:37:45 %2B0100." <9911171037.ZM24889@cs.vu.nl>
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This is what I think you said :-)
/sys/dev/hfa/fore_output.c:
/*
* don't do this...
*/
#ifdef GGM
xdp->xd_rate = FORE_DEF_RATE;
#else
/*
* given target max_pcr of 74460 I have to work out
* the rate, where rate is the fusion of data and idle as 16-bit fields
* joined in a 32.
*
* Linux does this:
*
*fore200e_rate_ctrl(struct atm_qos* qos, struct tpd_rate* rate)
*{
* if (qos->txtp.max_pcr < ATM_OC3_PCR) {
*
* compute the data cells to idle cells ratio from the PCR
* rate->data_cells =
* qos->txtp.max_pcr * FORE200E_MAX_BACK2BACK_CELLS /
* ATM_OC3_PCR;
* rate->idle_cells = FORE200E_MAX_BACK2BACK_CELLS -
* rate->data_cells;
* }
* else {
* disable rate control
* rate->data_cells = rate->idle_cells = 0;
* }
*}
*
* typedef struct tpd_rate
* {
* BITFIELD2(
* u32 idle_cells : 16, number of idle cells to insert
* u32 data_cells : 16 number of data cells to transmit
* )
* } tpd_rate_t;
*
* values found for the #defines from Linux are:
*
* #define FORE200E_MAX_BACK2BACK_CELLS 255
*
* and from atm_h for FreeBSD I get:
*
* #define ATM_PCR_OC3C 353207 Peak Cell Rate for OC3c
*
* so I used BC to calculate the date_cells and idle_cells values
* as (74460*255/353207)=53 and (255-53)=202 respectively.
* on a PC, this becomes a u_long value of 3473610
*/
xdp->xd_rate = 3473610;
#endif
--
George Michaelson | DSTC Pty Ltd
Email: ggm@dstc.edu.au | University of Qld 4072
Phone: +61 7 3365 4310 | Australia
Fax: +61 7 3365 4311 | http://www.dstc.edu.au
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