Hi,
I'm working on a custom beagleboard platform based on the OMAP3503
processor.
I have a Freescale Zigbee radio module connected to the SPI bus, and it is to
be used for flashing the radio module's firmware image.
I am using a program derived from the spidev_test.c file in the
android-2.6.32-kernel/Documentation/spi folder.
The android linux kernel is a standard rowboat linux kernel based, which
includes TI's platform support for OMAP35x from TI's arago OMAP PSP project.
The problem that I am having is that the first bit of every SPI byte transfer
received from the slave zigbee module is a zero.
For example, 0xEA when transmitted, comes out as 0x6A.
Here is an example message transmit and receive sequence. The zigbee module
sends a zero for the first byte transferred, and then echoes the first byte
sent, as a response in a subsequent transfer, as an acknowledgement.
Number of elements read from the firmware update file into the transmit buffer
= 16
Displaying the contents of the transmit buffer array
55 10 00 EA 76 10 00 EA 7D 10 00 EA 84 10 00 EA
Displaying the contents of the receive buffer array
00 00 55 10 00 6A 76 10 00 6A 7D 10 00 6A 04 10
Number of bytes received = 16 bytes
Similarily, 0x84 changes to 0x04.
Looking at the binary representation,
0xEA = 1110 1010
0x6A = 0110 1010
0x84 = 1000 0100
0x04 = 0000 0100
>From the above pattern, it looks like I'm losing the most significant bit for
>every 8-bit (1 byte) transfer.
Looking at the data pattern, the ones that come back correctly are the ones
that don't need the 8th bit set to represent its value, e.g. 0x50, 0x10, 0x00,
etc.
What could be causing the first bit stuck at 0 ?
Elvis Dowson
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