UM0851 datasheet(92/245 Pages) STMICROELECTRONICS

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Communication device drivers

UM0851

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Doc ID 16604 Rev 2

return after completion of transfer.*/

return spi_sync(spi, &m);

}

4.6.4

Un-registering the driver

On module exit, the SPI slave driver must be un-registered with the SPI framework. This is

accomplished by calling spi_unregister_driver(&eeprom_driver).

4.6.5

Known issues or limitations

There are some known issues with the current controller driver and current slave drivers.

●

The SPI controller supports data transfer with EEPROM chip up to 1 MHz in interrupt

mode. Actually, the depth of the Tx FIFO is 8 bytes/half words. Transmit interrupt

comes at half FIFO empty condition. Therefore, if the speed is 2 MHz, then it will take

only 16 us to transmit 4 bytes of data. However, interrupt latency in Linux is around 16

us. Therefore, by the time the interrupt handler passes more data to the FIFO, the older

data is completely transmitted. The timeout for the EEPROM chip is one clock cycle. So

the data transfer is terminated at that point.

●

The SPI controller supports data transfer with EEPROM chip up to 21 MHz in DMA

mode.

4.6.6

SPI device driver performance

The performance measurement has been performed using:

●

Hardware: ARM926EJS (333MHz), SPEAr600 and SPEAr300 boards.

●

Kernel: linux-2.6.27

4.6.7

Configuration options

4.6.8

References

●

SPI master framework in linux "drivers/spi/ and include/linux/spi/" for Linux 2.6.27

●

SPEAr SPI driver "drivers/spi/spr_ssp_pl022.c" and "drivers/spi/spr_ssp_pl022.h".

●

SPI master framework documentation Documentation/spi / folder.

Table 30.

SPI driver configuration options

Configuration option

Comment

CONFIG_SPI_MASTER

This option enables the SPI Master framework in

Linux.

CONFIG_SPEAR_SSP_MASTER_PL022

This option enables the SPEAr SPI PL022 driver.

CONFIG_SPI_EEPROM

This option enables the EEPROM driver

CONFIG_SPI_SPIDEV

This option enables the PIDEV driver.

CONFIG_SPEAR_DMAC_PL080

This option enables the SPI transfers in DMA

mode by enabling support for SPEAr DMAC

PL080 driver.

CONFIG_SPI_DEBUG

This option enables SPI debug prints.

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