Programming the Ethernet controller

Interface

 * See also: Ethernet packets
 * See also: Ethernet state diagram

The eight states
There are eight major states to the module.

State list

 * (000) Reset Cycle
 * The reset cycle resets the selected chips. There are flags for resetting all 4 chips: DAC, ADC, temperature sensor, Ethernet controller.  This is the entry state from a power-on.  From this state, proceed unconditionally to 001.


 * (001) Transmit "I"
 * This state transmits an "I" packet to acknowledge that a reset occurred but the board is now prepared to accept new packets and function normally. From this state, proceed unconditionally to 010.


 * (010) Idle
 * This is the idle state where the state machine awaits a new packet's arrival. If the Receive FIFO is empty, it loops back on itself and continues checking the FIFO.  If the FIFO is not empty, proceed to 011.


 * (011) Read Packet
 * This state accesses the first packet. If packets need to be filtered by the FPGA, this state will filter and return to 010 on a bad packet.  The MAC data is discarded, as it is unimportant to the FPGA, and the first data byte is read.  This byte is used as a switch: an ASCII "R" loops to 000.  A "Q" proceeds to 100.  A "P" proceeds to 110.  Any other value is a bad packet and the state machine returns to 010.


 * (100) Poll Status
 * This state polls the status chips (the ADC and the temperature sensor) so that recent data is ready for transmission.


 * (101) Transmit "S"
 * This state packages and transmits an "S" packet over the Ethernet to report back the status of the board in response to a "Q" packet.


 * (110) Program DAC
 * This state programs the DAC with new values according to the mask and data in the "P" packet.


 * (111) Transmit "D"
 * This state packages and transmits a "D" packet over the Ethernet to report back the DAC voltages in response to a "P" packet.

State interconnect
These states will form the outline of the functional block diagram. Within each state will be a smaller process or set of processes, possibly broken into substates. Additionally we will have a central state register. Each block reads the state value in the register and enables itself upon seeing its own value. After completion of its function, a block will write a new value to the state register to enable the next block.

State variable
Based on the assignments of state values to the various states, certain interpretations of the state's bits arise. They may or may not prove useful in coding the system. They are given here in the case that they do become useful.
 * S2:1:
 * S2 = 0: "Core cycle" that executes regularly and forms the spine of the state diagram.
 * S2:1 = 00: "Initialization cycle" that prepares the state diagram for normal functioning.
 * S2:1 = 01: "Standard cycle" that the state machine returns to most frequently to process appropriate switching to branches.
 * S2 = 1: "Branch cycles" that execute selectively based on received packets.
 * S2:1 = 10: "Query cycle" as described in the page on Ethernet packets.
 * S2:1 = 11: "Programming cycle" as described in the page on Ethernet packets.
 * S0:
 * S0 = 0: "Setup state" to prepare internal workings for a communication.
 * S0 = 1: "Transfer state" to communicate with the external PC.

Controller

 * transceiver
 * This block provides a level of abstraction between the precise CP2200/1 interface and a generalized interface seen by the internal blocks of the FPGA. It takes information on the next transfer to carry out and returns information on the last transfer completed.  It has a pulse signal to begin a transfer and a pulse signal to notify of a completed transfer.  This eliminates a need for the internal workings of the FPGA to be aware of the timing of the interface; it simply begins a transfer and waits for notification of the transfer's completion.
 * inputs
 * CLK: clock
 * /Rst: asynchronous, active-low reset
 * Go: pulse to begin a transmission
 * R/W_in: read/write toggle: active-high read, active-low write
 * A_in: 8-bit bus for address to read to/write from
 * D_in: 8-bit bus for data to write; ignored during a read
 * outputs to internals
 * Done: pulse to signal completion of a transmission
 * R/W_out: read/write flag: active-high read, active-low write
 * A_out: 8-bit bus for address of last read/write
 * D_out: 8-bit bus for data of last read; internal systems should ignore for a write
 * outputs to CP2200/1
 * /CS: active-low chip select
 * MotEn: Motorola/Intel format toggle: active-high Motorola, active-low Intel
 * MuxEn: Multiplexed flag; not used for CP2201
 * ALE: ALE strobe
 * /Wr: Active-low write flag
 * /Rd: Active-low read flag
 * inouts
 * AD: 8-bit address and data bus
 * state register
 * A three-bit register to store the current state.
 * inputs
 * Clk: clock
 * /Rst: asynchronous, active-low reset to zero the register (puts system into reset state)
 * En: write enable
 * D: three-bit data-in bus
 * outputs
 * Q: three-bit data-out bus

(000) Reset Cycle
Block 000 will have four functional blocks: one each for the DAC, ADC, and Ethernet controller, and one to coordinate their completion. The temperature sensor lacks an external reset function; it self-initializes on startup. The "R" packet will supply flags as to whether or not to enable the various blocks. A power-on reset will default to resetting all components. Using the enable flags like a mask on the done lines, the fourth functional block will update the state register. For information on the reset procedures, see Reset and Initialization.

inputs
 * Clk: clock
 * /Rst: asynchronous, active-low reset
 * State: 3-bit state value
 * D_En: DAC enable, assume held high/low by previous block
 * A_En: ADC enable, assume held high/low by previous block
 * E_En: Ethernet enable, assume held high/low by previous block

internal signals
 * S_En: state enable, S_En <= not (St(2) or St(1) or St(0))
 * Go: when S_En goes high Go pulses for one cycle
 * D_Go: DAC reset go pulse, D_Go <= Go and D_En
 * A_Go: ADC reset go pulse, A_Go <= Go and A_En
 * E_Go: Ethernet reset go pulse, E_Go <= Go and E_En

blocks
 * DAC Reset
 * Resets and initializes the DAC.
 * inputs
 * Clk: clock
 * /Rst: asynchronous, active-low reset
 * D_Go: go pulse to begin reset/initialization process
 * outputs
 * - All DAC reset/initialization control lines -
 * D_Done: goes high when reset/initialization process is complete, falls on D_Go pulse
 * ADC Reset
 * Resets and initializes the ADC.
 * inputs
 * Clk: clock
 * /Rst: asynchronous, active-low reset
 * A_Go: go pulse to begin reset/initialization process
 * outputs
 * - All ADC reset/initialization control lines -
 * A_Done: goes high when reset/initialization process is complete, falls on A_Go pulse
 * Ethernet Reset
 * Resets and initializes the Ethernet controller.
 * inputs
 * Clk: clock
 * /Rst: asynchronous, active-low reset
 * E_Go: go pulse to begin reset/initialization process
 * outputs
 * - All Ethernet reset/initialization control lines -
 * E_Done: goes high when reset/initialization process is complete, falls on E_Go pulse
 * Coordinator
 * Coordinates the completion of each reset cycle and notifies other blocks that the reset process is complete.
 * inputs
 * Clk: clock
 * /Rst: asynchronous, active-low reset
 * D_En: high when DAC is to be reset
 * D_Done: high when DAC is done resetting
 * A_En: high when ADC is to be reset
 * A_Done: high when ADC is done resetting
 * E_En: high when Ethernet controller is to be reset
 * E_Done: high when Ethernet controller is done resetting
 * internal signals
 * Flag <= (D_Done or not D_En) and (A_Done or not A_En) and (E_Done or not E_En)
 * outputs
 * Done: when Flag goes high, Done pulses for one cycle; connects to state register as an enable
 * New_St: new state to be written to the state register; goes to 001 while Done is high

(001) Transmit "I"
This is a simple state. It loads to the CP2200/1 a packet containing an ASCII "I" in the first byte and padding (zeros) in all remaining bits. The CP2200/1 may handle padding itself; this will have to be verified in the data sheet. After the transmission is complete, the block writes a 010 to the state register.

(010) Idle
Block 010 continuously polls the interrupt registers on the CP2200/1 until the Receive FIFO Empty flag comes back as a zero. On this condition it transitions to state 011.

inputs:
 * Clk: clock
 * /Rst: asynchronous, active-low reset
 * State: 3-bit state value
 * TxRx_A: 8-bit address from transceiver
 * TxRx_D: 8-bit data from transceiver
 * TxRx_Done: pulse from transceiver to signal transfer complete

internal signals
 * S_En: state enable, S_En <= not St(2) and St(1) and not St(0)
 * Go: when S_En goes high Go pulses for one cycle

blocks
 * Fetcher
 * Reads register 0x76 (INT0RD) by sending a read request to the transceiver
 * inputs
 * F_Go: pulse to start request, F_Go <= Go or Loop
 * outputs
 * TxRx_Go: Go line on transceiver
 * TxRx_R/W: R/W line on transceiver, tied high (read)
 * TxRx_A: A_in bus on transceiver, tied to 0x76 (0111 0110)
 * Note: D_in on transceiver is not used; assume this line defaults to zero
 * Looper
 * Switch to determine if this state should loop on itself or continue to the next state.
 * inputs
 * S_En: state enable
 * TxRx_Done: Done pulse from transceiver
 * TxRx_Data: D_out bus from transceiver
 * outputs
 * Loop: pulse to repeat fetch cycle; Loop <= S_En and TxRx_Done and TxRx_Data(6)
 * Done: pulse to finish state; connects to state counter as an enable in order to increment the state to 011; Done <= S_En and TxRx_Done and not TxRx_Data(6)

(011) Read Packet
Block 011 is the first block with switching between following states. Its first task is to load the MAC data of the packet. If filtering inside of the FPGA is required, this block is responsible for it. The only MAC filtering likely to be needed is a check to see if the destination MAC address matches the MAC address of the CP2200/1, but the CP2200/1 should filter this itself (verify in the data sheet). If the packet is bad, this block tells the CP2200/1 to skip the packet and returns to block 010. The MAC filter would be the first substate.

After MAC filtering comes the second substate (or the only substate if MAC filtering is found to be unnecessary). This reads the first byte of the packet's data and uses it as a switch to determine the transition to the next state: Anything other than the three defined packets is considered a bad packet and is discarded in the CP2200/1 before transitioning back to state 010. An "R" packet obtains the reset mask from the second byte then discards the packet before transitioning to state 000. State 000 assumes that the reset mask is held, so this output needs to be latched in place until the next time this block activates. "Q" and "P" packets simply transition to the next state, allowing the following states to access the rest of the packet.

(100) Poll Status
This block will have at least two functional blocks: one to poll the temperature sensor and one to poll the ADC. Its job is to update all status values from the status chips in preparation for transmission. Once all status values have been updated it transitions to state 101.

(101) Transmit "S"
This block compiles the status values into a single packet by loading them into the CP2200/1 in a defined order and format, including padding/converting any values that need it. Once the packet has been sent, it discards the received packet and transitions to state 010. ''Note: Received packet can be discarded anywhere in state 100 or 101. The discard functionality may even be relocated to the end of state 011, as that state already interacts with the CP2200/1.''