I found a bug in the I2C interface for the Mica platform(ATM128L) in TinyOS
2.x (2.0.2). In particular, after line 322 in file
Atm128I2CMasterPacketP.nc the code should be changed as follows:
/* Note #define ATM128_I2C_SLA_WRITE 0x00
* #define ATM128_I2C_SLA_READ 0x01
*/
if (state == I2C_ADDR) {
if (reading == TRUE) {
call I2C.write(((packetAddr<<1) & 0xff) | ATM128_I2C_SLA_READ);
}
else
call I2C.write(((packetAddr<<1) & 0xff) & (~ATM128_I2C_SLA_READ));
// Note that this is redundant since the shift should shift in
a "0"
Reasons:
1. According to the Atmel 128L user guide pg 213, the address should be sent
as SLA+R or SLA+W where SLA is a 7-bit slave address. The way
Atm128I2CMasterPacketP is currently written, the result of an address write
actually appears shifted "right", e.g., 0x48 become 0x24 on the I2C bus.
2. Additionally, if someone happens to have the least significant bit set, a
simple OR with ATM128_I2C_SLA_WRITE will make it appear as if the master is
attempting a read.
The code snippet above fixes both of those errors. I can attach the
fully-modified code should anyone need it. It should be noted that the
MSP430 doesn't have the same problem since it has separate "own" and "slave"
address registers.
It should also be noted that the TOS 2x release has two of the same headers
for ATM128I2C.h that will cause a compiler error for I2C, but I wrote about
that in an earlier email.
Regards,
Kurt Peters, P.E.
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