Timeline for Setting SPI chip select every few bytes with buffered read
Current License: CC BY-SA 3.0
8 events
| when toggle format | what | by | license | comment | |
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| Mar 12, 2018 at 13:45 | comment | added | joan | @MaxWalczak I'd be interested to know what throughput improvement you can manage with that change. It could be significant or irrelevant depending on how the driver works. | |
| Mar 12, 2018 at 13:40 | vote | accept | Max Walczak | ||
| Mar 12, 2018 at 13:40 | comment | added | Max Walczak | This seems to solve my problem quite exactly! Thank you a lot for your time and effort. | |
| Mar 12, 2018 at 12:47 | comment | added | joan | You need to look at the spi_ioc_transfer structure. Each member is one SPI transaction. The cs_change will presumably set the CS change around that transaction. You pass an array of those structures to the SPI transfer. If this is not how you/wiringPi are handling multiple transactions then I've wasted your time (although it's quite easy to write your own version in C, wiringPi is a thin wrapper around the SPI driver). | |
| Mar 12, 2018 at 12:18 | comment | added | Max Walczak | Can you elaborate on how is the cs_change executed? If I have spi.len of 128 bits and set bits per word to 16, will it turn CS on and off every 16 bits being transferred? That is exactly what I would want to achieve. | |
| Mar 12, 2018 at 11:42 | comment | added | joan |
I have not tested multiple SPI requests with the kernel driver. There is a spi.cs_change field in the C IOCTL. Perhaps edit the wiringPi source wiringPiSPI.c and change the value to 1 and then rebuild the library. That might then toggle the chip select at each transaction.
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| Mar 12, 2018 at 11:34 | comment | added | Max Walczak | Does it mean that when I call a single read in a loop it will be much faster than the equivalent with Linux SPI driver? Thanks a lot for the link - I've been looking for something like this for a long time and I found nothing! From the plots I can see that the speed is almost the same as with linux spi driver at 3 bytes per sample and 2MHz | |
| Mar 12, 2018 at 10:44 | history | answered | joan | CC BY-SA 3.0 |