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<p class=MsoNormal><span lang=EN-US>Hi,<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>I’m on a mpc5121 platform, kernel
2.6.24.6, and I’m using the mpc512x_psc_spi driver to communicate with
a touch screen controller.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>I’m sending commands and reading data
from the controller using 24-bit packet (3 bytes).<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>The speed of the SPI is set to 640 KHz.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>I thought that I would need 8/640K = 12,5
us each byte I send, but this is not true.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>I’m verifying the time needed by mpc512x_psc_spi_transfer_rxtx
function in order to send one byte toggling a digital output when it sets the
TX/RX flags (after it copies data in the transmission buffer) and toggling the
output again when the empty buffer interrupt is triggered.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>I see that the actual 12,5us data transfer
is preceded by a 20us delay and followed by another 15,6us delay. So the
transfer is done in almost 50 us.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Is this a normal behavior? Does the PSC
controller need this overhead in the transfer time?<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>DSCKI and DTL delays are set to zero.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Another doubt I have:<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>In mpc512x_psc_spi_transfer_rxtx, Mode Register
2 of the PSC is set to zero. This is done (as manual says) by access to MR1 (by
a read) and then write a zero on the same address.:<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>in_8(&psc->mode);<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>mdelay(1);<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>out_8(&psc->mode, 0x0);<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>mdelay(1);<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>I don’t understand why a 1ms delay is
needed. The manual doesn’t say anything about this.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>I tried to comment out these delays and anyway
it seems to work correctly.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Best regards,<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Matteo Canella<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><o:p> </o:p></p>
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