31.6.2.4 Silent Access
When silent access is enabled , the logical size of the TRAM is divided by two to store each byte of data and its 1’s complement (CompData) in the whole physical TRAM size .
The differential write and silent read processes are transparent and managed by the TRAM controller , The TRAM executes the following process on data access :
• When the CPU writes to the TRAM, the data and its bit-wise invert are stored into the RAM.
• When the CPU reads from the TRAM, both the data and its bit-wise invert are retrieved from the RAM. If the TRAM cannot verify that both values complement each other, a bus error is returned.
When silent access is enabled , the data stored in the TRAM must be accessed using the logical mapping shown in TRAM logical mapping table:
Byte 3 | Byte 2 | Byte 1 | Byte 0 | TRAM Register |
---|---|---|---|---|
Data | Data | Data | Data | RAM0 |
... | ... | ... | ... | ... |
Data | Data | Data | Data | RAM[63] |
Reserved | Reserved | Reserved | Reserved | RAM[64] |
... | ... | ... | ... | ... |
Reserved | Reserved | Reserved | Reserved | RAM[127] |
Only 8-bit (byte) access and 16-bit (half-word) access are supported in this mode. 32-bit (word) write accesses are ignored and 32-bit (word) read accesses return 0.
All accesses to the reserved area of the TRAM are discarded and generate a bus error.
The physical mapping of the TRAM when silent access is enabled, is represented in TRAM physical mapping table:
Byte 3 | Byte 2 | Byte 1 | Byte 0 | TRAM Register |
---|---|---|---|---|
CompData | Data | CompData | Data | RAM0 |
CompData | Data | CompData | Data | RAM1 |
CompData | Data | CompData | Data | RAM2 |
... | ... | ... | ... | ... |
CompData | Data | CompData | Data | RAM[127] |
When used in addition of data scrambling , the TRAM controller automatically manage both scrambling and differential data storage operation on specific data access.