Memory map: Difference between revisions
Jump to navigation
Jump to search
Content added Content deleted
| Line 104: | Line 104: | ||
Accesses in this area are affected by a simplified hardware implementation of the RCP SysAD bus, so '''''access size is ignored'''''. This means that: |
Accesses in this area are affected by a simplified hardware implementation of the RCP SysAD bus, so '''''access size is ignored'''''. This means that: |
||
* Reads: RCP will ignore the requested access size and will just put the requested 32-bit word on the bus. Luckily, this is the correct behavior for 8-bit and 16-bit accesses (as explained above), so the VR4300 will be able to extract the correct portion. |
* Reads: RCP will ignore the requested access size and will just put the requested 32-bit word on the bus. Luckily, this is the correct behavior for 8-bit and 16-bit accesses (as explained above), so the VR4300 will be able to extract the correct portion. 64-bit reads instead will completely freeze the VR4300 (and thus the whole console), because it will stall waiting for the second word to appear on the bus that the RCP will never put. |
||
* Writes: RCP will ignore the requested access size and just write the word that was put on the bus directly into the hardware register. For 8-bit and 16-bit accesses, this means that the shifted value prepared by the VR4300 is the one that will be written verbatim. Reprising the example above, if <code>S0=0x1234'5678</code>, <code>A0=0x0460'0011</code>, running <code>SB S0, 0(A0)</code> will write the value <code>0x5678'0000</code> to the RCP hardware register <code>0x0460'0010</code>. For 64-bit accesses, as they are written on the bus MSB-first, the RCP will write the MSB to the hardware register, ignoring the LSB. |
* Writes: RCP will ignore the requested access size and just write the word that was put on the bus directly into the hardware register. For 8-bit and 16-bit accesses, this means that the shifted value prepared by the VR4300 is the one that will be written verbatim. Reprising the example above, if <code>S0=0x1234'5678</code>, <code>A0=0x0460'0011</code>, running <code>SB S0, 0(A0)</code> will write the value <code>0x5678'0000</code> to the RCP hardware register <code>0x0460'0010</code>. For 64-bit accesses, as they are written on the bus MSB-first, the RCP will write the MSB to the hardware register, ignoring the LSB. |
||