[U-Boot] U-Boot Makefile question

[Steven Zedeck <saz@proliphix.com>]

Hi all,
I am new to u-boot. But I am ramping up pretty fast. My primary issue is
understanding the Makefile syntax. Is there a good tutorial somewhere that
explains how u-boot uses the Makefiles and their syntax?

For example, I'm having problems understanding what this means in a
Makefile:

COBJS-$(CONFIG_HAS_DATAFLASH) += at45.o
COBJS-$(CONFIG_FLASH_CFI_DRIVER) += cfi_flash.o
COBJS-$(CONFIG_HAS_DATAFLASH) += dataflash.o
COBJS-$(CONFIG_FLASH_CFI_LEGACY) += jedec_flash.o
COBJS-$(CONFIG_MW_EEPROM) += mw_eeprom.o

COBJS	:= $(COBJS-y)
SRCS	:= $(COBJS:.o=.c)
OBJS	:= $(addprefix $(obj),$(COBJS))

This is from drivers/mtd/Makefile.

How does COBJS get initially defined upon entry into the Makefile?

Does at45.o get added to the list of objects to be built only if the
CONFIG_HAS_DATAFLASH flag is set?

What does the "-" sign mean before the "$" ?

What does this mean?  COBJS	:= $(COBJS-y)

I'm sorry for the "dumb" questions. Any help with the understanding of
Makefiles would be greatly appreciated.

Thanks in advance,
Steve
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