Workshopband als PDF - Mpc.belwue.de

MPC-WORKSHOP FEBRUAR 2013
Figure 3: Transmitter
line encloses the whole token and data packet structure.
As inputs of the whole block there are 7 lines to
write into the registers what wants to be transmitted,
and two “run” lines (Drun & THrun) which enables
the process to send either the data or the token and
handshake packets. As outputs there are the two differential
lines for the USB along with the oeb to control
the output driver line if necessary.
1) Interface with the microcontroller
There are 4 inputs dedicated to the parallel data
which can be either an address of a specific register to
write to, or the data that needs to be written. Furthermore,
it can be the upper or a lower nibble of a byte;
two lines are used (a0 & a1) to signal which one it is
according to Table 3. The address is decoded and the
load is sent to the corresponding register.
2) Token and Handshake Packets Structure
The structure has several registers to save the data
that will be transmitted; their addresses are stated on
Table 4. The CTRL register provides important information
about what will be sent out and how. Bit 6, if
set, means a token packet (32 bits) will be sent, otherwise
only a handshake (16 bits).
The calculated CRC and the SOF are loaded from
the CRC calculator and the SOF generator respectively.
While the bit 5 from the CTRL register dictates
whether the calculated CRC or the stored CRC will be
used, the bit 7 activates the host’s functions, i.e., SOF
generation.
Table 3: Interface Data Types
a1 a0 Data Type
0 0 Lower nibble of Data
0 1 Upper nibble of Data
1 0 Lower nibble of Address
1 1 Upper nibble of Address
Table 4: Token and Handshake Registers
Address Register
0x00 SYN
0x01 PID
0x02 ADDR
0x03 ENDP
0x04 CRC stored
0x05 SOF PID
--- SOF
---
CRC
calculated
0x0F CTRL
The SOF generator increments the SOF number and
gives a pulse to begin the transmission at the
appropriate time. The register structure is designed to
be able to change, from sending any token packet to
send a SOF packet, easily.
In order to maintain control between sending a
normal token, handshake or a data packet and sending
the SOF packets two steps are taken. First, in the clock
block issues a warning signal to announce the
proximity of the new SOF; if the warning signal is
high, no transmission should take place. The second
step consists of a state machine to avoid conflicts
between sending SOF and the two run signals. The
highest priority is given to the SOF packets; if a conflict
arises and both Drun and THrun signals are activated
simultaneously, the sending of token and handshake
packets will have priority.
Every block is controlled by the Control State Machine
for Token and Handshake Packets. When the
run signal is activated, it enables the output and pushes
the data out, validating every bit with a data valid
signal, and receiving feedback from the bit stuffing
block in case a zero bit needs to be inserted. It takes
into account if a token or a handshake packet will be
sent, by keeping track of the number of bits. Once the
PID is sent it enables the CRC calculator and disables
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