CEC1712 datasheet(90/338 Pages) MICROCHIP

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CEC1712

DS00003416C-page 90

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6.0

RAM AND ROM

6.1

SRAM

The CEC1712 contains two blocks of SRAM. The two SRAM blocks in the CEC1712 total 256KB. Both SRAM blocks

can be used for either program or data accesses. Performance is enhanced when program fetches and data accesses

are to different SRAM blocks, but a program will operate correctly even if both program and data accesses are targeting

the same block simultaneously.

• The first SRAM, which is optimized for code access, is 224KB

• The second SRAM, which is optimized for data access, is32KB

6.2

ROM

The CEC1712 contains a 64KB block of ROM, located at address 00000000h in the ARM address space. The ROM

contains boot code that is executed after the de-assertion of RESET_SYS. The boot code loads an executable code

image into SRAM. The ROM also includes a set of API functions that can be used for cryptographic functions, as well

as loading SRAM with programs or data.

6.3

Additional Memory Regions

6.3.1

ALIAS RAM

The Alias RAM region, starting at address 20000000h, is an alias of the SRAM located at 118000h, and is the same

size as that SRAM block. EC software can access memory in either the primary address or in the alias region; however,

access is considerably slower to the alias region. The alias region exists in order to enable the ARM bit-band region

located at address 20000000h.

6.3.2

RAM BIT-BAND REGION

The RAM bit-band region is an alias of the SRAM located at 118000h, except that each bit is aliased to bit 0 of a 32-bit

doubleword in the bit-band region. The upper 31 bits in each doubleword of the bit-band region are always 0. The bit-

band region is therefore 32 times the size of the SRAM region. It can be used for atomic updates of individual bits of the

SRAM, and is a feature of the ARM architecture.

The bit-band region can only be accessed by the ARM processor. Accesses by any other bus master will cause a mem-

ory fault.

6.3.3

CRYPTOGRAPHIC RAM

The cryptographic RAM is used by the cryptographic API functions in the ROM

6.3.4

The Register bit-band region is an 32-to-1 alias of the device register space starting at address 40000000h and ending

with the Host register space at 400FFFFF. Every bit in the register space is aliased to a byte in the Register bit-band

region, and like the RAM bit-band region, can be used by EC software to read and write individual register bits. Only the

EC Device Registers and the GPIO Registers can be accessed via the bit-band region.

A one bit write operation to a register bit in the bit-band region is implemented by the ARM processor by performing a

read, a bit modification, followed by a write back to the same register. Software must be careful when using bit-banding

if a register contains bits have side effects triggered by a read.

The bit-band region can only be accessed by the ARM processor. Accesses by any other bus master will cause a mem-

ory fault.

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