This introduces a new majoe mode, FPGA_MAJOR_MODE_OFF_LF, which should ONLY be used in sending loops for LF. Basically the PWR_LO is set HIGH in order to discharge voltage faster.
Once sending is over, the normal FPGA_MAJOR_MODE_OFF SHALL be used.
Reader and card simulation have almost no common code. Moreover the sim
uses an SSP Clock at 212kHz for all timings to prevent any drifting from
the PRNG. This clock speed is not available in reader simulation mode (SSP
runs at up to 3.4MHz, and changes speed between TX and RX). For these
reasons having the code in separate files makes it significantly cleaner.
TC1 counts the number of TC0 overflows (carry bits).
In random conditions TC1 would return or stay at zero,
instead of counting up. This due to the behavior of the
reset signal.
SAM7S Series Datasheet, 33.5.6 Trigger:
Regardless of the trigger used, it will be taken into account
at the following active edge of the selected clock. This means
that the counter value can be read differently from zero just
after a trigger, especially when a low frequency signal is
selected as the clock.
The new code first prepares TC1 and asserts TC1 trigger and
then prepares TC0 and asserts TC0 trigger. The TC0 start-up
will reset TC1.
I've tried to modulate the Legic specific pause-puls using ssc and the default
ssc clock of 105.4 kHz (bit periode of 9.4us) - previous commit. However,
the timing was not precise enough. By increasing the ssc clock this could
be circumvented, but the adventage over bitbang would be little.
- Even tough legic tags transmit just AM using xcorrelation
results in a significantly better signal quality.
- Switching from bit bang to a hardware based ssc frees
up CPU time for other tasks e.g. demodulation
I've tried to modulate the Legic specific pause-puls using ssc and the default
ssc clock of 105.4 kHz (bit periode of 9.4us) - previous commit. However,
the timing was not precise enough. By increasing the ssc clock this could
be circumvented, but the adventage over bitbang would be little.
- Even tough legic tags transmit just AM using xcorrelation
results in a significantly better signal quality.
- Switching from bit bang to a hardware based ssc frees
up CPU time for other tasks e.g. demodulation
