Project Assembly Steps
2.1 Main Block: CAN Controller (can_controller_std)
The can_controller_std is the heart of the system. It implements the standard CAN protocol (11-bit ID), being responsible for sending and receiving CAN frames on the bus. This block manages communication, organizes data packets, controls message transmission and monitoring, and provides status signals that are used by the rest of the system.
Main Functions:
- Transmit CAN frames with custom data (in this case, the message "HELLO").
- Receive CAN frames from the bus.
- Signal transmission and reception interrupts.
- Work together with a UART controller to display received data.
2.2 CAN Controller Block Inputs
To function properly, the can_controller_std requires different control, configuration, and data signals. Below, we organize these inputs into three categories: main inputs, configuration parameters, and data for the message to be transmitted.
a) Main Inputs
These inputs control the basic operation and synchronization of the block.
| Input | Source | Description |
| clk_i | Global system clock | Synchronizes all internal operations of the CAN controller. |
| rst_i | InvertedC (reset) | Active-low reset that initializes the CAN controller when necessary. |
| rx_i | Physical IO70 pin | Receives data from the CAN bus (CAN RX). |
| tx_request_i | one_hz_clock (1 Hz pulse) | Requests the CAN controller to transmit a frame every second. |
| clear_irq_i | InvertedC from key button | Manually clears transmission interrupts, allowing new transmissions. |
b) Configuration Parameters
These signals configure the bit timing and message filtering of the CAN protocol. They determine the transmission speed and which messages are accepted on the bus.
| Parameter | Value | Description |
| tx_data_0_i | 8'd72 | H (first byte of the "HELLO" message) |
| time_segment_1_i | 4'd15 | Defines the first segment of the bit time in the CAN protocol. It controls part of the CAN communication timing, assisting with signal synchronization. |
| baud_r_presc_i | 3'd2 | Prescaler for the CAN protocol clock. Defines the timing base which, together with the time segments, determines the CAN transmission speed. Example: 125 Kbps. |
| sync_jump_width_i | 1'b0 | Defines the Synchronization Jump Width (SJW). With 0, there is no margin for bit time adjustments in case of small variations. |
| time_segment_2_i | 2'b01 | Second time segment in the CAN protocol. Controls the final part of the bit time, important for completing transmission synchronization. |
| acceptance_code_i | 11'h000 | Acceptance code for filtering received CAN messages. A value of 000 means any message ID will be accepted (no filtering). |
| acceptance_mask_i | 11'h000 | Acceptance mask that defines which bits of acceptance_code_i are relevant. With 000, filtering is disabled and all messages are accepted. |
c) Data to Be Transmitted
These signals are responsible for loading the information that composes the message transmitted on the CAN bus. In this project, we want to send the string "HELLO", consisting of 5 characters.
| Signal | Value | Description |
| rtr_i | 1'b0 | Mensagem de dados normal. |
| packet_id_i | 11'h257 | ID da mensagem no barramento CAN. |
| packet_length_i | 4'd5 | "HELLO" tem 5 caracteres ➡️ 5 bytes. |
| tx_data_0_i | 72 | Letter H (ASCII 72). |
| tx_data_1_i | 69 | Letter E (ASCII 69). |
| tx_data_2_i | 76 | Letter L (ASCII 76). |
| tx_data_3_i | 76 | Letter L (ASCII 76). |
| tx_data_4_i | 79 | Letter O (ASCII 79). |
2.3 System Outputs
a) Outputs of the can_controller_std Block
The outputs of the can_controller_std block are responsible for:
- Transmitting CAN frames on the bus.
- Indicating the status of operations (message transmission and reception).
- Providing received data to other system modules, such as the UART debug interface.
These outputs enable both physical communication via CAN and system monitoring through UART and LEDs.
| Output | Destination | Function |
| tx_o | IO71 | Transmits the CAN frame on the bus. |
| transmit_irq_o | LED0 | Indicates that the transmission has started. |
| transmit_ack_irq_o | LED1 | Confirms that the transmission was acknowledged (ACK). |
| receive_irq_o | uart_can_std_printer | Signals that a CAN frame has been received. |
b) Outputs of the uart_can_std_printer Block
In addition to the direct outputs of the can_controller_std, there are components that process this information and provide user feedback through LEDs and UART.
| Output | Destination | Function |
| uartTxPin | uartTx | Sends the received message via UART (ASCII). |
| txDone | LED5 | Indicates that the UART transmission is complete. |
And at the end, your project should be something like this:
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