Module fieldsafe 

A probe-rs probe driver for our tag bases, using only the ST-LINK commands every base in the field supports.

The bases present as ST-LINK/V2s, but there is no record of which base firmware is in the field, and some of it is old. probe-rs’s own ST-LINK driver relies on two things those bases get wrong: READ_DAP_REG (bases flashed before 773db79a return stale data) and the 2-byte reply to a 1-byte READMEM_8BIT (no base sends it). This driver never depends on either. It speaks only the subset tagcore’s LinkAdapt already uses on every base:

• USB open, mode query, DFU exit, SWD enter/exit, nRST drive, voltage;
• READMEM_32BIT / WRITEMEM_32BIT with the last-R/W-status check, in chunks of at most CHUNK bytes;
• READDEBUGREG for the chip ID, which tells L4 from U3.

Everything else probe-rs asks for is answered here:

• DAP register reads are answered from a table of the part’s real values (DPIDR, the AP0 IDR, BASE and CSW, “no AP” past AP0, and 0 for any other register, CFG included); DAP writes are accepted and ignored, because memory never goes through DRW/TAR – it goes through the base’s own memory commands, which set up the AP themselves.
• 8- and 16-bit memory accesses are done with 32-bit ones: reads take the bytes they need; writes read, patch and write back whole words. That is safe for SRAM and flash-algorithm buffers, which is what probe-rs uses them for, but would not be for a peripheral register with side effects.

Reset and SWD entry happen in tagcore’s order: nRST is asserted before SWD is entered, because a tag asleep with its debug domain off answers SWD only from reset.

The layering is FieldSafeProbe (a probe-rs [DebugProbe]) -> FieldSafeArm (its [ArmDebugInterface]) -> FieldSafeMemory (AP0’s [ArmMemoryInterface]). None of them is thread-safe; probe-rs drives a session from one thread at a time. The C++ host tools have no counterpart: they call STM32_Programmer_CLI for programming. See also host/libraries/tagprobe-rs/design/architecture.md.

Structs

DapTable 🔒

What the driver answers for the target’s DAP registers.

FieldSafeArm

The ARM debug interface over a FieldSafeProbe.

FieldSafeMemory

AP0 memory through the base’s 32-bit memory commands.

FieldSafeProbe

The probe: a tagcore LinkAdapt opened on one base.

LinkError

A link failure, reported to probe-rs as a probe-specific error.

Constants

CHUNK

Largest single memory transfer, in bytes, as tagcore’s TagMonitor uses.

L4_DAP 🔒

STM32L4 (Cortex-M4): SW-DP v1 and an AHB-AP.

L4_DBGMCU_IDCODE 🔒

Address of DBGMCU_IDCODE on the STM32L4.

PIN_NRESET 🔒

nRESET in the swj_pins bit map (the CMSIS-DAP DAP_SWJ_Pins layout probe-rs uses).

U3_DAP 🔒

STM32U3 (Cortex-M33): SW-DP v2 and an AHB5-AP. AP values read from an STM32U375 through a base whose READ_DAP_REG works.

U3_DBGMCU_IDCODE 🔒

Address of DBGMCU_IDCODE on the STM32U3.

Functions

addr32 🔒

Narrows a probe-rs 64-bit address to the 32-bit address the base takes.

link_err 🔒

Wraps a failed step, named by what, as a probe-rs [DebugProbeError::ProbeSpecific].

plausible 🔒

Reports whether an IDCODE read looks real: a device ID (low 12 bits) of all zeros or all ones is what a wrong address or a failed bus returns.