On Wed, Apr 10, 2013 at 08:36:12AM -0700, Ron K. Jeffries wrote: > Werner, > > *You do amazing work. Full stop.* > > Does spi-jz470-gpio only require the UBB board to interface to the outside > world using spi?
If I understood correctly, Werner only talked about atben performance tests, the wireless thing. It's not about general SPI. Regards, Lluís. > On Wed, Apr 10, 2013 at 7:43 AM, Werner Almesberger > <[email protected]>wrote: > > > [ Also posted on the linux-zigbee hardware list. No cross-post, since > > few people will be on both lists. ] > > > > What this is all about > > ---------------------- > > > > The ATBEN board on the Ben NanoNote needs a bit-banging SPI driver. > > There are several ways to implement this, ranging from reuse of the > > generic spi-gpio driver to an optimized driver that's specific for > > this platform. > > > > I implemented several such approaches and measured their performance > > in the Ben NanoNote. Below are my findings. > > > > Comments welcome. > > > > > > Cast and characters > > ------------------- > > > > spi_atben_gpio: NanoNote-specific framework for setting up the > > AT86RF230/1 with SPI-GPIO or one of the optimized drivers (below). > > The name derives from spi_atben (see below) and should be changed > > (maybe to atben_spi or atben_spi_gpio ?) since it is not an SPI > > driver but merely a framework that provides configuration data and > > performs miscellaneous platform setup. > > > > https://github.com/wpwrak/ben-wpan-linux/blob/master/drivers/net/ieee802154/spi_atben_gpio.c > > > > spi_atben: like spi_atben_gpio, but contains a highly optimized > > SPI driver for the ATBEN configuration in the Ben NanoNote. > > > > https://github.com/wpwrak/ben-wpan-linux/blob/master/drivers/net/ieee802154/spi_atben.c > > > > spi-jz4740-gpio: SPI-GPIO driver optimized for the Jz4740. Uses the > > optimized register accesses from spi_atben but pin assignment is not > > restricted to ATBEN. The only limitation is that MOSI, MISO, and > > SCLK must be on the same port. > > > > https://github.com/wpwrak/ben-wpan-linux/blob/master/drivers/spi/spi-jz4740-gpio.c > > > > spi-gpio-atben: task-specific SPI-GPIO driver using the #include > > "spi-gpio.c" method. Replaces gpiolib functions with register > > accesses specific to the ATBEN configuration in the Ben NanoNote. > > Note that some of the code could be moved into Jz4740 > > architecture-specific GPIO support. > > > > https://github.com/wpwrak/ben-wpan-linux/blob/master/drivers/spi/spi-gpio-atben.c > > > > In the following sections, we abbreviate the stack configurations > > as follows: > > > > Abbreviation Framework Transport Chip driver > > --------------- --------------- --------------- ----------- > > spi-gpio spi_atben_gpio spi-gpio at86rf230 > > spi-gpio-atben spi_atben_gpio spi-gpio-atben at86rf230 > > spi-jz4740-gpio spi_atben_gpio spi-jz4740-gpio at86rf230 > > spi_atben spi_atben at86rf230 > > > > > > Measurements > > ------------ > > > > Access time to AT86RF231 registers and buffer, in microseconds, on > > an otherwise idle Ben NanoNote: > > > > Driver read from 0x51 read 120 bytes from buffer > > | | write 0x0a to 0x15 write 1 byte to buffer > > (0x33) > > | | | read 1 byte from buffer write 120 bytes > > | | | | | | | > > spi-gpio 81 85 186 1696 97 1596 > > spi-gpio-atben 63 59 123 498 65 437 > > spi-jz4740-gpio 10 8 21 280 10 231 > > spi_atben 10 7 21 280 10 230 > > > > Data rate for hypothetical buffer accesses of infinite length. > > I.e., kbps = 1000*119*8/(t_write120-t_write1) > > > > Driver buffer read (kbps) buffer write (kbps) > > --------------- ----------------------- ------------------- > > spi-gpio 630 635 > > spi-gpio-atben 2549 2559 > > spi-jz4740-gpio 3676 4308 > > spi_atben 3676 4327 > > > > At the air interface, IEEE 802.15.4 has a data rate of 250 kbps. > > The AT86RF231 transceiver also supports non-standard higher data > > rates up to 2 Mbps. > > > > Driver(s) Code size (lines) > > --------------------------------------- ----------------- > > spi_atben_gpio 128 > > spi_atben_gpio + spi-gpio-atben 128+ 53 > > spi_atben_gpio + spi-jz4740-gpio 128+416 > > spi_atben 423 > > > > > > Computational cost > > ------------------ > > > > The high-level operations of sending and receiving produce the > > following major low-level operations: > > > > Operation register buffer waitqueue > > read write read write > > --------------- ------- ------- ------- ------- --------- > > reception 1 - 1 - 1 > > transmission 9 4 - 1 1 > > > > Using the measured data from above, we get the following total > > computational overhead in microseconds, without considering the > > waitqueue scheduling delay: > > > > Driver reception transmission > > 1 120 127 1 120 125 (bytes) > > --------------- ------- ------- ------- ------- ------- ------- > > spi-gpio 267 1777 1866 1166 2665 2727 > > spi-gpio-atben 186 561 583 868 1240 1256 > > spi-jz4740-gpio 31 290 304 132 353 362 > > > > Note that the minimum frame length in IEEE 802.15.4 is 5 bytes. > > The values for 125 (excluding CRC) and 127 (including CRC) bytes > > are extrapolated. > > > > According to [1], maximum-sized frames can be sent/received, > > including CSMA/CA and acknowledgement, at a rate between one > > every 4928 us and one every 7168 us. > > > > We would therefore get the following maximum CPU load: > > > > Driver Reception Transmission > > --------------- --------------- ------------ > > spi-gpio 38% 55% > > spi-gpio-atben 12% 25% > > spi-jz4740-gpio 6% 7% > > > > > > Observations > > ------------ > > > > spi-gpio needs the smallest amount of new code but is also very > > inefficient, making it questionable whether this configuration > > would yield acceptable performance in regular use. > > > > With spi-gpio-atben, only a small amount of code is added, but > > buffer accesses become almost 4 times faster. Register reads and > > writes are still fairly slow. > > > > spi_atben and spi-jz4740-gpio both achieve the best performance > > without significant differences between them. Both add a complete > > SPI driver. Of the two, spi-jz4740-gpio is preferable, because it > > uses the nearly universal spi_atben_gpio framework driver. > > > > > > Conclusion > > ---------- > > > > I think performance trumps most other considerations in this case. > > spi-gpio is clearly too inefficient. spi_atben_gpio with > > spi-jz4740-gpio offers the best performance and has a low impact > > on the system load (< 10%). In case this solution would be met > > with strong resistance for some reason, spi-gpio-atben would offer > > a compromise between performance and the amount of code. > > > > > > References > > ---------- > > > > [1] > > http://www.jennic.com/files/support_files/JN-AN-1035%20Calculating%20802-15-4%20Data%20Rates-1v0.pdf > > > > _______________________________________________ > > Qi Hardware Discussion List > > Mail to list (members only): [email protected] > > Subscribe or Unsubscribe: > > http://lists.en.qi-hardware.com/mailman/listinfo/discussion > > > _______________________________________________ > Qi Hardware Discussion List > Mail to list (members only): [email protected] > Subscribe or Unsubscribe: > http://lists.en.qi-hardware.com/mailman/listinfo/discussion _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
