ecspi

Linux SPI driver for Elias Crespin art projects involving Gumstix Overo computers.

Kernel Config

The default gumstix kernels assign drivers to the two SPI CS pins that are exposed on the expansion card header.

Since only one SPI driver can be assigned to each BUS.CS pin, the ecspi module won't load unless you first modify your kernel.

This is the code in the board-overo.c file that we have to disable.

static struct spi_board_info overo_spi_board_info[] __initdata = {
#if defined(CONFIG_TOUCHSCREEN_ADS7846) || \
	defined(CONFIG_TOUCHSCREEN_ADS7846_MODULE)
	{
		.modalias		= "ads7846",
		.bus_num		= 1,
		.chip_select		= 0,
		.max_speed_hz		= 1500000,
		.controller_data	= &ads7846_mcspi_config,
		.irq			= OMAP_GPIO_IRQ(OVERO_GPIO_PENDOWN),
		.platform_data		= &ads7846_config,
	},
#elif defined(CONFIG_SPI_SPIDEV) || defined(CONFIG_SPI_SPIDEV_MODULE)
	{
		.modalias		= "spidev",
		.bus_num		= 1,
		.chip_select		= 0,
		.max_speed_hz		= 1000000,
		.mode			= SPI_MODE_0,
	},
#endif
#if defined(CONFIG_PANEL_LGPHILIPS_LB035Q02) || \
	defined(CONFIG_PANEL_LGPHILIPS_LB035Q02_MODULE)
	{
		.modalias		= "lgphilips_lb035q02_panel-spi",
		.bus_num		= 1,
		.chip_select		= 1,
		.max_speed_hz		= 500000,
		.mode			= SPI_MODE_3,
	},
#elif defined(CONFIG_SPI_SPIDEV) || defined(CONFIG_SPI_SPIDEV_MODULE)
	{
		.modalias		= "spidev",
		.bus_num		= 1,
		.chip_select		= 1,
		.max_speed_hz		= 1000000,
		.mode			= SPI_MODE_0,
	},
#endif
};

If you are building from the latest gumstix kernel, linux-omap3-2.6.36, then the changes to the defconfig can be accomplished with the following sed calls.

sed -i 's:CONFIG_TOUCHSCREEN_ADS7846=m:# CONFIG_TOUCHSCREEN_ADS7846 is not set:g' defconfig
sed -i 's:CONFIG_PANEL_LGPHILIPS_LB035Q02=y:# CONFIG_PANEL_LGPHILIPS_LB035Q02 is not set:g' defconfig
sed -i 's:CONFIG_SPI_SPIDEV=y:# CONFIG_SPI_SPIDEV is not set:g' defconfig

The defconfig file can be found here

overo-oe/org.openembedded.dev/recipes/linux/linux-omap3-2.6.36/defconfig

After making the changes, clean the old kernel and rebuild it and the rootfs.

$ bitbake -c clean virtual/kernel
$ bitbake virtual/kernel
$ bitbake <image>   // something like omap3-console-image

Build Instructions

Standard external to tree Linux kernel module Makefile is included.

There is also a environment file that can be sourced if using the standard OE build system that Gumstix suggests.

The build assumes that you have a built kernel in your OETMP working directories. You will if you built a kernel as above.

Operation

To be completed.

For testing, the driver repeatedly outputs two 192 byte spi_transfers out SPI bus 1, CS 1 (SPI1.1). The two spi_transfers are packaged in one spi_message with a CS line pulse between the spi_transfers.

The data is monotonically increasing integers.

The time between spi_messages is controlled via an hrtimer whose frequency is currently constant, determined by the module parameter write_frequency.