pd: check for collisions before transmitting

Added check for collision just before transmitting on CC line.
To check for collision, RX monitoring is left on all the time
(except when in the act of receiving or transmitting, or in
between receiving and sending a goodCRC), and a
simple check for RX transmission started is used to see if the
CC line is idle or not.

RX monitoring is also changed to only trigger on 3 edges within
20us, as per the PD spec.

When a collision is detected by seeing that CC is not idle, the
transmitting packet is dropped.

BUG=chrome-os-partner:30135
BRANCH=samus
TEST=load onto samus and zinger. make sure we negotiate and make
sure custom VDMs succeed. enabled pings and made sure we stay
alive with pings for a few min.

Also added code to pd_rx_handler to toggle a test point on EVT
board to verify the timing of when we get RX interrupts:

Change-Id: I22d172163319437d3d901e019eda79d4d592f6b8
Signed-off-by: Alec Berg <alecaberg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/226118
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

0 files changed, 0 insertions, 0 deletions