OCAH Memory Map

OCAH separates the chiplet-visible SMU aperture from the internal address maps used by SEP and SMC firmware. The chiplet integrator decides which system address range reaches the SMU external AXI input. Firmware then programs the SEP and SMC global base/size CSRs so the SMU crossbar can route incoming traffic to the correct inbound port.

Table 1 distinguishes the chiplet envelope, programmable apertures, and internal address maps.

Table 1. OCAH address-map configuration layers
Concept	Configured by	Purpose	Example
Chiplet NoC envelope	Integrator / chiplet address map	Controls which external-master addresses reach SMU `ext_in`	Example only: 64 MiB total SMU aperture
SEP global aperture	SEP firmware via `SEP_GLOBAL_BASE_ADDR` / `SEP_REGION_SIZE`	Controls SMU `ext_in` to `sep_in` routing and SEP inbound global-to-local remap	Example only: 32 MiB SEP slot in a 32 MiB + 32 MiB SEP/SMC partition
SMC global aperture	SMC firmware via `GLOBAL_BASE` / `REGION_SIZE`	Controls SMU `ext_in` to `smc_in` routing and SEP-to-SMC decode	Example only: 32 MiB SMC slot in a 32 MiB + 32 MiB SEP/SMC partition

External masters use chiplet-global addresses and are bounded first by the chiplet NoC decode. The SMU crossbar applies the firmware-programmed SEP and SMC global apertures to route those transactions to sep_in or smc_in. Subsystem-internal CPU maps and local aliases are described in the SEP and SMC chapters.

At reset, SEP_GLOBAL_BASE_ADDR is 0x0000_0000 and the SMC’s GLOBAL_BASE register is 0x4000_0000. Their separate size registers, SEP_REGION_SIZE and SMC REGION_SIZE, both reset to 0x0100_0000 (16 MiB). The corresponding half-open address ranges are therefore [0x0000_0000, 0x0100_0000) for SEP and [0x4000_0000, 0x4100_0000) for SMC.

The global base addresses and region sizes are software-programmed and must not overlap. The hardware does not derive them from a chiplet ID. The Programmer’s Guide gives the aperture programming sequence for early boot.

Register tables throughout this manual report each field’s software access as a compact token in their Access column; Register Field Access Notation decodes that notation.

1. Decode Response Codes

The SMC, SEP, Key Manager and cross-trigger network address maps state, for each unit, how a 32-bit access that no register or memory backs is answered. A cell reads read response, read data / write response, for example DECERR, 0xBADCAB1E / DECERR. OKAY, SLVERR and DECERR are the AXI response codes returned on RRESP and BRESP. The read data is the word a 32-bit read returns in either half of a 64-bit data bus. Where the two halves differ, a note on the cell gives the word returned when address bit 2 is set.

The Hole in Extent column covers an unbacked offset inside the unit’s decoded extent. Where the space between a wrapper’s sub-blocks, or the padding after each element of an array, answers differently, the cell names it separately as between sub-blocks or between instances.
The Past Extent column covers the rest of the unit’s aperture, the range its Size column gives.
A Reserved row is an address between unit apertures.

A register block generated from SystemRDL answers an access that reaches it as follows:

An offset between its registers answers OKAY: a read returns 0 and a write has no effect.
An offset past the end of its last register answers SLVERR with read data 0. That end is a multiple of the block’s register width, so an access wider than the registers that runs past it, such as a 64-bit read of the last register of a block with 32-bit registers, answers SLVERR.

A block instantiated as an array at a stride wider than one instance answers OKAY at every offset, so the padding between instances behaves as a hole. The alias and output remap regions, the traffic filter entries, the GPIO interfaces and the cross-trigger ports are such blocks.

Whether a unit’s Past Extent cell shows this SLVERR depends on the decoder in front of the block. Where the fabric decodes the unit’s extent exactly, the fabric answers first.

Table 2. Decode response codes
Code	Meaning
`OKAY`	The access completes. A read returns the listed data, and a write has no effect.
`SLVERR`	The access reaches a component that refuses it.
`DECERR`	No unit or sub-block claims the address, and a decoder refuses the access before it reaches one.
Aliases registers	The access reaches a live register at another offset, which answers it.
Forwarded	The subsystem passes the access on without decoding it, and its target answers.
Adopter-defined	The adopter’s implementation answers.
`-`	The region does not exist: the unit is memory, its registers fill its extent, or its aperture ends at its extent.