Referring to the Comportable guideline for peripheral device functionality, the module entropy_src has the following hardware interfaces defined
- Primary Clock:
clk_i
- Other Clocks: none
- Bus Device Interfaces (TL-UL):
tl
- Bus Host Interfaces (TL-UL): none
- Peripheral Pins for Chip IO: none
| Port Name | Package::Struct | Type | Act | Width | Description |
|---|
| entropy_src_hw_if | entropy_src_pkg::entropy_src_hw_if | req_rsp | rsp | 1 | |
| cs_aes_halt | entropy_src_pkg::cs_aes_halt | req_rsp | req | 1 | Coordinate activity between CSRNG’s AES and Entropy Source’s SHA3. The idea is that Entropy Source requests CSRNG’s AES to halt and waits for CSRNG to acknowledge before it starts its SHA3. While SHA3 runs, Entropy Source keeps the request high. CSRNG may not drop the acknowledge before Entropy Source drops the request. |
| entropy_src_rng_enable | logic | uni | req | 1 | Signal through which entropy_src enables the noise source. entropy_src will keep this signal high as long as it expects the noise source to operate. This is not a flow control signal through which entropy_src would exert backpressure on the noise source; rather this signal stays high while entropy_src is enabled. |
| entropy_src_rng_valid | logic | uni | rcv | 1 | Acknowledgement signal from the noise source. When ‘1’, it indicates that the entropy_src_rng_bit data is valid and ready to be consumed. |
| entropy_src_rng_bits | logic | uni | rcv | RngBusWidth | Output data bus carrying the raw entropy bits from the noise source. These bits are valid when entropy_src_rng_valid is asserted. The width is determined by RngBusWidth parametrization. |
| entropy_src_xht_valid | logic | uni | req | 1 | Valid signal for the external health test interface. When asserted, it indicates that entropy_src_xht_bits, entropy_src_xht_bit_sel, and entropy_src_xht_meta are valid for consumption by the external health test. |
| entropy_src_xht_bits | logic | uni | req | RngBusWidth | Carries the raw entropy data from the entropy source to be consumed by the external health test module. The data on this bus is valid when entropy_src_xht_valid is asserted. The width is determined by RngBusWidth parametrization. |
| entropy_src_xht_bit_sel | logic | uni | req | RngBusBitSelWidth | Provides bit selection information for the raw entropy data. It specifies which specific bit or subset of bits from entropy_src_xht_bit should be used. The width is determined by RngBusBitSelWidth parametrization. |
| entropy_src_xht_health_test_window | logic | uni | req | HealthTestWindowWidth | Provides the window size of the health in bits. |
| entropy_src_xht_meta | entropy_src_pkg::entropy_src_xht_meta | req_rsp | req | 1 | |
| otp_en_entropy_src_fw_read | prim_mubi_pkg::mubi8 | uni | rcv | 1 | |
| otp_en_entropy_src_fw_over | prim_mubi_pkg::mubi8 | uni | rcv | 1 | |
| rng_fips | logic | uni | req | 1 | |
| tl | tlul_pkg::tl | req_rsp | rsp | 1 | |
| Interrupt Name | Type | Description |
|---|
| es_entropy_valid | Event | Asserted when entropy source bits are available for firmware for consumption via ENTROPY_DATA register. |
| es_health_test_failed | Event | Asserted whenever the main state machine is in the alert state, e.g., due to health tests failing and reaching the threshold value configured in ALERT_THRESHOLD. |
| es_observe_fifo_ready | Event | Asserted when the observe FIFO has filled to the configured threshold level (see OBSERVE_FIFO_THRESH). |
| es_fatal_err | Event | Asserted when an fatal error condition is met, e.g., upon FIFO errors, or if an illegal state machine state is reached. |
| Alert Name | Description |
|---|
| recov_alert | This alert is triggered upon the alert health test threshold criteria not met. |
| fatal_alert | This alert triggers for any condition detected in the ERR_CODE register, which includes FIFO errors, COUNTER errors, FSM state errors, and also when integrity failures are detected on the TL-UL bus. |
| Countermeasure ID | Description |
|---|
| ENTROPY_SRC.CONFIG.REGWEN | Registers are protected from writes. |
| ENTROPY_SRC.CONFIG.MUBI | Registers have multi-bit encoded fields. |
| ENTROPY_SRC.CONFIG.REDUN | Threshold register has an inverted copy to compare against. |
| ENTROPY_SRC.INTERSIG.MUBI | OTP signal used to enable software access to registers. |
| ENTROPY_SRC.MAIN_SM.FSM.SPARSE | The ENTROPY_SRC main state machine uses a sparse state encoding. |
| ENTROPY_SRC.ACK_SM.FSM.SPARSE | The ENTROPY_SRC ack state machine uses a sparse state encoding. |
| ENTROPY_SRC.RNG.BKGN_CHK | Random number generator is protected with continuous background health checks. |
| ENTROPY_SRC.FIFO.CTR.REDUN | The FIFO pointers of several FIFOs are implemented with duplicate counters. |
| ENTROPY_SRC.CTR.REDUN | Counter hardening for all health test counters. |
| ENTROPY_SRC.CTR.LOCAL_ESC | Redundant counter failures will cause a local escalation to the main state machine. |
| ENTROPY_SRC.ESFINAL_RDATA.BUS.CONSISTENCY | Comparison on successive bus values for the post-conditioned entropy seed bus. |
| ENTROPY_SRC.TILE_LINK.BUS.INTEGRITY | Tilelink end-to-end bus integrity scheme. |