[ECOS] forwarded message from Peter Graf

[Jesper Skov]

To : Jesper Skov <jskov at redhat dot com>
Subject : Re: [ECOS] Hitachi SH7709 Serial drivers
>From : pg-itk at t-online dot de (Peter Graf)
Date : Fri, 17 Nov 2000 10:57:21 +0100
References : <pg-itk@t-online.de's message of "Thu, 12 Oct 2000 16:17:54 +0200"><3.0.5.32.20001012161754.008f0560@pop.btx.dtag.de>

Hi Jesper,

thanks for your help with the Hitachi SH7709A serial drivers. One thing I
forgot to report is that the eCos bitrate computation doesn't work
correctly under all conditions. For 20 MHz all works well. The table below
shows the values computed by hand and the values computed by eCos.

Peripheral Clock = 20 MHz:

Bitrate
[bit/s]   n     N       min. error      N eCos  error eCos
4800      0     129     0,16%           129     0,16%
9600      0     64      0,16%           64      0,16%
14400     0     42      0,94%           42      0,94%
19200     0     32      -1,36%          31      1,73%
38400     0     15      1,73%           15      1,73%
57600     0     10      -1,36%          9       8,51%
115200    0     4       8,51%           4       8,51%
230400    0     2       -9,58%          1       35,63%

For 22 MHz eg. 38400 baud doesn't work reliably under eCos. The table below
shows the correct values and the values computed by eCos. (BTW 22 MHz
peripheral clock is very useful because it allows low bitrate errors up to
230 kBaud.)

Peripheral Clock = 22 MHz:

Bitrate
[bit/s]  n      N       min. error      N       error eCos
9600      0     71      -0,54%          70      0,87%
14400     0     47      -0,54%          46      1,58%
19200     0     35      -0,54%          34      2,31%
38400     0     17      -0,54%          16      5,32%
57600     0     11      -0,54%          10      8,51%
115200    0     5       -0,54%          4       19,36%
230400    0     2       -0,54%          1       49,20%

I have only worked around by using a fixed table. A parametric macro
without the rounding problems seems tricky, if you want to avoid
computation at runtime.

Peter