RISC-V Trace Encoder Driver

Overview

The esp_riscv_trace component provides the public driver API for the RISC-V trace encoder peripheral. The driver is enabled by CONFIG_ESP_RISCV_TRACE_ENABLE and creates one encoder handle per selected core during startup auto-initialization.

Applications can override the weak esp_riscv_trace_get_user_config(int core_id) function to customize the startup configuration per core (each encoder can be configured independently), or use Kconfig defaults through ESP_RISCV_TRACE_DEFAULT_CONFIG().

State Transition

stateDiagram-v2
    [*] --> created: startup auto-init
    created --> started: esp_riscv_trace_start
    started --> stopped: esp_riscv_trace_stop
    stopped --> started: esp_riscv_trace_start

esp_riscv_trace_set_filter() and esp_riscv_trace_get_buffer() are only valid while the encoder is not started. esp_riscv_trace_get_status() can be used to read a coherent status snapshot.

Concurrency

Public driver APIs are serialized per trace core with a task-level lock. They are task-context APIs and must not be called from ISR context.

The driver keeps the lifecycle state check and the corresponding HAL register operation under the same per-core lock. This prevents concurrent callers from double-starting an encoder, racing a stop against filter programming, or reading the buffer before a stop has completed its cache synchronization.

Buffer and Trace Stream Notes

The trace buffer must be reachable by the trace encoder AHB master. Driver allocated buffers are placed in internal RAM or PSRAM according to configuration, and are cache-line aligned when that memory is reached through a data cache. Caller-provided buffers are validated for reachable memory and cache-line alignment. PSRAM placement is only available on targets whose encoder can reach external RAM (SOC_RISCV_TRACE_MEM_SUPPORT_PSRAM); on other targets the buffer is always internal.

In loop memory mode, wrapped buffers need periodic resynchronization packets to remain decodable after the original start sync has been overwritten.

Dependencies

This driver depends on the RISC-V trace HAL (part of the hal component) and currently targets SoCs that support the RISC-V trace encoder peripheral.

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