Status: Accepted
Owner: [email protected]
CC: jsuijs
Labels: Type-Defect Priority-Medium
New issue 120 by [email protected]: I2C, recieve correct data when it
should be incorrect data.
http://code.google.com/p/jallib/issues/detail?id=120
Recently while working on I2c echo and servo lib, I have found a
possible bug and I am able to re-produce this.
After writing i2c_sw_master_echo and i2c_hw_slave_echo to two PIC's,
and also changing the forever loop at the bottom of sw_master_echo to
this:
for 50_000 loop
pc_char = "A"
-- transmit to slave
-- we want to send 1 byte, and receive 1 from the slave
i2c_tx_buffer[0] = pc_char
var bit _trash = i2c_send_receive(icaddress, 1, 1)
-- receive buffer should contain our result
ic_char = i2c_rx_buffer[0]
serial_hw_write(ic_char) ;send recieved "B" to pc
end loop
I do get the expected result, which is 50_000 B's.
Then, if I completely erase the slave PIC, or if slave PIC is not working
correctly but has power, and do a reset of the master via CTS line (no
power off reset), I get the same result!
I was receiving correct data when I should have gotten incorrect data.
I use the -no-variable-reuse compiler option. I'm guessing there is a
byte somewhere in I2C that should get reset to 0 before receiving data
from the slave.
Step-by-step fault reproduction
1. get I2C working with I2C sw master and I2C hw slave echo samples.
2. replace the forever loop with the above code, it will still work & send
data via serial port with master as it should.
3. erase slave PIC via ICSP
4. reset master PIC via CTS
5. It will still work & send data via serial port on master, but it should
not!
master - 18f4620, bootloader
slave - 18f452, ICSP port
discussion is here:
http://groups.google.com/group/jallib/browse_thread/thread/4f86add865fd0347/07af1060520e7b47#07af1060520e7b47
Matt.
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