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I am running a display using SPI. When running it on my Pi Model B, everything runs fine and fast. But when connecting it to my Zero instead, it runs very slow.

Then I put the SD card of my Zero in my B -> the screen runs slow too, as on the Zero. So it's not a hardware but a software specific problem.

Hardware-SPI is enabled on both devices but while the Pi B has the spi_bcm2708 module enabled, the Zero runs on spi_bcm2835.

lsmod output on Pi B:

Module                  Size  Used by
binfmt_misc             6888  1
i2c_dev                 5587  0
snd_bcm2835            12808  0
snd_pcm                74834  1 snd_bcm2835
snd_seq                52536  0
snd_timer              19698  2 snd_seq,snd_pcm
snd_seq_device          6300  1 snd_seq
snd                    52489  5 snd_seq_device,snd_timer,snd_seq,snd_pcm,snd_bcm2835
snd_page_alloc          4951  1 snd_pcm
spidev                  5136  0
r8712u                165407  0
spi_bcm2708             4401  0
i2c_bcm2708             3681  0

On Pi Zero:

Module                  Size  Used by
cfg80211              499234  0
rfkill                 21397  2 cfg80211
r8712u                177928  0
snd_soc_bcm2835_i2s     6994  0
regmap_mmio             3728  1 snd_soc_bcm2835_i2s
snd_bcm2835            23131  0
snd_soc_core          164132  1 snd_soc_bcm2835_i2s
snd_pcm_dmaengine       5906  1 snd_soc_core
snd_pcm                95473  3 snd_bcm2835,snd_soc_core,snd_pcm_dmaengine
snd_timer              22556  1 snd_pcm
snd                    68400  4 snd_bcm2835,snd_soc_core,snd_timer,snd_pcm
i2c_bcm2708             5740  0
spi_bcm2835             7424  0
bcm2835_gpiomem         3823  0
bcm2835_wdt             4133  0
uio_pdrv_genirq         3718  0
uio                    10230  1 uio_pdrv_genirq
ipv6                  367671  26
  • Some information such as the SPI bus bits per second, transfers per second, and bytes per transfer for each Pi would help. – joan Dec 29 '16 at 15:08
  • Bus speed is 16 MHz and 2048 bytes/transfer on both. On Zero, this takes about 4 sec and on Pi B, it takes about 0.3-0.5 sec for each at a total of 150 transfers. – Ercksen Dec 29 '16 at 17:01
  • Have you benchmarked the SD card to see if it is too slow? – cybernard Feb 4 '17 at 14:40
  • Zero's SD card is even faster, this can not be the reason. – Ercksen Feb 5 '17 at 16:28
  • I read your answer and according to me, the pi zero has less processing power than the model B.You could try to change the SD card.See if it helps. – Krish Jan 18 '18 at 15:37
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If you are using a display with an X server or some other tools you can see too much slowness from RPIZero. The main causes are 2:

  1. RPIZero work only with 1 CPU (1 core, RPI 3B got 1 CPU with 4 core so is much better). So cannot parallelize operation much well
  2. RPIZero chipset is Broadcom2835 that is slower than the Broadcom2708
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