Memory map: Difference between revisions
Jump to navigation
Jump to search
Content added Content deleted
| Line 86: | Line 86: | ||
The physical memory map is implemented by RCP, as the VR4300 only talks directly to RCP. The bus between VR4300 and RCP is called [[SysAD Interface|SysAD]]. The RCP behaves differently with different access sizes depending on the specific area of the map and the subcomponent in charge of implementing it. |
The physical memory map is implemented by RCP, as the VR4300 only talks directly to RCP. The bus between VR4300 and RCP is called [[SysAD Interface|SysAD]]. The RCP behaves differently with different access sizes depending on the specific area of the map and the subcomponent in charge of implementing it. |
||
The SysAD bus is described at the hardware level in the [[SysAD Interface|SysAD page]], but to understand the effects on memory map it is sufficient to understand how data is marshalled for reads and writes. Since SysAD is a 32-bit bus, 32-bit accesses are the "native" ones, and the |
The SysAD bus is described at the hardware level in the [[SysAD Interface|SysAD page]], but to understand the effects on memory map it is sufficient to understand how data is marshalled for reads and writes. Since SysAD is a 32-bit bus, 32-bit accesses are the "native" ones, and the other access sizes are made in a weird way built upon a 32-bit data exchange. |
||
* Reads: VR4300 puts the address on the bus and the size of the access (8, 16, 32, 64). The RCP typically returns a full (aligned) 32-bit word address (or two, in case of a 64-bit read), from which the VR4300 extracts the correct portion. For instance, when reading 8-bit from address <code>0x0000'0001</code>, the RCP will put on the bus the 32-bit values at <code>0x0000'0000 - 0x0000'0003</code>, and the VR4300 will then just isolate the requested 8 bits. |
* Reads: VR4300 puts the address on the bus and the size of the access (8, 16, 32, 64). The RCP typically returns a full (aligned) 32-bit word address (or two, in case of a 64-bit read), from which the VR4300 extracts the correct portion. For instance, when reading 8-bit from address <code>0x0000'0001</code>, the RCP will put on the bus the 32-bit values at <code>0x0000'0000 - 0x0000'0003</code>, and the VR4300 will then just isolate the requested 8 bits. |
||