FreeBSD Device Drivers by Kong Joseph

Author:Kong, Joseph [Joseph Kong]
Language: eng
Format: epub
Tags: COMPUTERS / Operating Systems / UNIX
ISBN: 9781593274368
Publisher: No Starch Press
Published: 2012-04-29T16:00:00+00:00

Before I describe the functions defined in Example 10-1, note that the constant LED_IO_ADDR is defined as 0x404c and that the constant LED_NUM is defined as 2.

The following sections describe the functions defined in Example 10-1 in the order they would roughly execute.

led_identify Function

The led_identify function is the device_identify implementation for this driver. This function is required because the ISA bus cannot identify its children unaided. Here is the function definition for led_identify (again):

static void led_identify(driver_t *driver, device_t parent) { device_t child; child = device_find_child(parent, "led", −1); if (!child) { child = BUS_ADD_CHILD(parent, 0, "led", −1); bus_set_resource(child, SYS_RES_IOPORT, 0, LED_IO_ADDR, 1); } }

This function first determines if the ISA bus has identified a child device named "led". If it has not, then "led" is appended to the ISA bus’s catalog of identified children. Afterward, bus_set_resource is called to specify that I/O port access for "led" starts at LED_IO_ADDR.

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