Fri, 18 Jan 2013 17:18:50 +0000
[memory] Emulate main memory read wrap-around
3B1s with 512K or 1MB of base memory have a decoding quirk which causes reads
to 'wrap around'. That is to say, on a 512K machine, reading from addresses 0,
512K, 1024K or 1536K will address the same RAM byte. On a 1MB machine,
addresses 0 and 1024K address the same RAM byte.
Emulating this incorrectly causes P4TEST to report an incorrect amount of
available base RAM.
| src/memory.c | file | annotate | diff | revisions |
1.1 diff -r 4c03f6433d0d -r 8b24770dea79 src/memory.c 1.2 --- a/src/memory.c Wed Jan 16 00:41:51 2013 +0000 1.3 +++ b/src/memory.c Fri Jan 18 17:18:50 2013 +0000 1.4 @@ -11,7 +11,8 @@ 1.5 // The value which will be returned if the CPU attempts to read from empty memory 1.6 // TODO (FIXME?) - need to figure out if R/W ops wrap around. This seems to appease the UNIX kernel and P4TEST. 1.7 #define EMPTY 0xFFFFFFFFUL 1.8 -// #define EMPTY 0x55555555UL 1.9 +//#define EMPTY 0x55555555UL 1.10 +//#define EMPTY 0x00000000UL 1.11 1.12 /****************** 1.13 * Memory mapping 1.14 @@ -737,10 +738,8 @@ 1.15 // RAM access 1.16 uint32_t newAddr = mapAddr(address, false); 1.17 if (newAddr <= 0x1fffff) { 1.18 - if (newAddr >= state.base_ram_size) 1.19 - return EMPTY & 0xffffffff; 1.20 - else 1.21 - return RD32(state.base_ram, newAddr, state.base_ram_size - 1); 1.22 + // Base memory wraps around 1.23 + return RD32(state.base_ram, newAddr, state.base_ram_size - 1); 1.24 } else { 1.25 if ((newAddr <= (state.exp_ram_size + 0x200000 - 1)) && (newAddr >= 0x200000)) 1.26 return RD32(state.exp_ram, newAddr - 0x200000, state.exp_ram_size - 1); 1.27 @@ -789,10 +788,8 @@ 1.28 // RAM access 1.29 uint32_t newAddr = mapAddr(address, false); 1.30 if (newAddr <= 0x1fffff) { 1.31 - if (newAddr >= state.base_ram_size) 1.32 - return EMPTY & 0xffff; 1.33 - else 1.34 - return RD16(state.base_ram, newAddr, state.base_ram_size - 1); 1.35 + // Base memory wraps around 1.36 + return RD16(state.base_ram, newAddr, state.base_ram_size - 1); 1.37 } else { 1.38 if ((newAddr <= (state.exp_ram_size + 0x200000 - 1)) && (newAddr >= 0x200000)) 1.39 return RD16(state.exp_ram, newAddr - 0x200000, state.exp_ram_size - 1); 1.40 @@ -841,10 +838,8 @@ 1.41 // RAM access 1.42 uint32_t newAddr = mapAddr(address, false); 1.43 if (newAddr <= 0x1fffff) { 1.44 - if (newAddr >= state.base_ram_size) 1.45 - return EMPTY & 0xff; 1.46 - else 1.47 - return RD8(state.base_ram, newAddr, state.base_ram_size - 1); 1.48 + // Base memory wraps around 1.49 + return RD8(state.base_ram, newAddr, state.base_ram_size - 1); 1.50 } else { 1.51 if ((newAddr <= (state.exp_ram_size + 0x200000 - 1)) && (newAddr >= 0x200000)) 1.52 return RD8(state.exp_ram, newAddr - 0x200000, state.exp_ram_size - 1);