RE: SPI Bus Speed depending on CPU frequency of the DS80C400 TINI OS 1.12?

Since TINI uses a software SPI library it is only capable of 100Kbits/s.  It
takes much longer to control the signals directly by software than just
getting and putting bytes into a register for a hardware SPI solution.

Faster clock speeds will yield higher throughput.

Some on this list have implemented a hardware SPI solution in the CPLD
(U12).



> -----Original Message-----
> From: tini-admin-6tN4nzCoH/[email protected] [mailto:tini-admin-6tN4nzCoH/[email protected]]On Behalf Of
> Peter in Afrika
> Sent: Wednesday, May 19, 2004 7:39 AM
> To: tini-6tN4nzCoH/[email protected]
> Subject: [TINI]SPI Bus Speed depending on CPU frequency of the DS80C400
> TINI OS 1.12?
>
>
> Hello list,
>
> According to the documentation of the SPI Class ->
>
>     This class is a thin wrapper over a bit-bang SPI native library.
>     The bit-bang SPI port is implemented using pins ... (PCE0\-PCE3\) of
>     the DS80C390. This is a master only implementation. P5.4 (PCE0\) =
>     SSCK (Serial clock) P5.5 (PCE1\) = MOSI (Master Out/Slave In) P5.6
>     (PCE2\) = MISO (Master In/Slave Out) P5.7 (PCE3\) = SS (Slave select)
>
>         * Max data rate is 100Kbit/s. Lower frequencies are specified
>           using a clock delay value that can be set using the
>           setClockDelay method.
>
>     Note on noskew option: Do not attempt to use the noskew option of
>     this SPI library with a *Large* Data Array. Using noskew turns off
>     interrupts on TINI and will cause UNPREDICTABLE system behavior and
>     watch dog reboots sending of a *Large* data array is attempted.
>
> the MAX DATA Rate is about 100Kbit. Why is this set to this small value
> (according to SPI specification the max value allowed is 1 Mbit!), and
> how does this value depend on the CPU frequency? Is it compared to a
> TINI m400 Board with 29.xx MHz and do I have the 2.5 times faster access
> with a 73.728 Mhz Board??
>
> And: Does this Max value belong to the fact, that TIMER3 and TIMER1 are
> used for serial port timings and so there is no way to clock it correctly?
> Has anybody made experiences with higher speeds on the SPI Bus and could
> share this experience?
>
> kind regards
> Peter
>
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