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| − | {{WARNING|This page is still in the proposal stage and should not yet be considered an official specification.}}
| + | #REDICT [[NEO mapper/Extension]] |
| − | | |
| − | Proposal for an extension to the [[NEO mapper]] format.
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| − | | |
| − | == Specifications ==
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| − | | |
| − | === Principles ===
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| − | | |
| − | Any write operation to the NEO mapper with address bits 10-12 set to 0 is considered as access to extended features. In that case, the mapper bank register is not modified.
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| − | | |
| − | All other write operations should be considered normal access to the mapper's bank register.
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| − | | |
| − | The address contains an 8-bit function ID, and a 3-bit destination bank value for function to be applied to a given mapper's bank.
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| − | | |
| − | {|
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| − | |-
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| − | |
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| − | {| class="wikitable"
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| − | |+ ADDRESS
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| − | |-
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| − | ! 15 || 14 || 13 || 12 || 11 || 10 || 9 || 8 || 7 || 6 || 5 || 4 || 3 || 2 || 1 || 0
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| − | |-
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| − | |style="background-color:#BBB;" colspan="2"| Page
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| − | |style="background-color:#FAA;"| 0
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| − | |style="background-color:#FAA;"| 0
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| − | |style="background-color:#FAA;"| 0
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| − | |style="background-color:#AAF;" colspan="3"| Bank
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#AAF;" colspan="4"| Function
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| − | |}
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| − | |
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| − | {| class="wikitable"
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| − | |+ DATA
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| − | |-
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| − | ! 7 || 6 || 5 || 4 || 3 || 2 || 1 || 0
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| − | |-
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| − | |style="background-color:#AAF;" colspan="8"| Parameter
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| − | |}
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| − | |}
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| − | | |
| − | === Functions ===
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| − | ==== 0x00: ROM mapper ====
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| − | Activate access to the cartridge ROM mapper through the given bank (default mode)
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| − | | |
| − | Parameter:
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| − | {| class="wikitable"
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| − | ! 8 || 7 || 6 || 5 || 4 || 3 || 2 || 1
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| − | |-
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |}
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| − | | |
| − | ==== 0x01: Cartridge information ====
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| − | Activate read access to the cartridge information data through the given bank (8 KB mirrored on NEO-16)
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| − | | |
| − | Parameter:
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| − | {| class="wikitable"
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| − | ! 8 || 7 || 6 || 5 || 4 || 3 || 2 || 1
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| − | |-
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |}
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| − | | |
| − | ==== 0x02: ''Reserved'' ====
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| − | | |
| − | ==== 0x03: RAM ====
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| − | Activate read/write access to RAM through the given bank
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| − | | |
| − | Parameter:
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| − | {| class="wikitable"
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| − | ! 8 || 7 || 6 || 5 || 4 || 3 || 2 || 1
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| − | |-
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| − | |style="background-color:#AAF;" colspan="8"| RAM segment
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| − | |}
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| − | | |
| − | ==== 0x04: SRAM/FRAM ====
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| − | Activate read/write access to SRAM/FRAM through the given bank (8 KB mirrored on NEO-16)
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| − | | |
| − | Parameter:
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| − | {| class="wikitable"
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| − | ! 8 || 7 || 6 || 5 || 4 || 3 || 2 || 1
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| − | |-
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#AAF;" colspan="4"| Segment
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| − | |}
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| − | | |
| − | ==== 0x05: ''Reserved'' ====
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| − | | |
| − | ==== 0x06: ''Reserved'' ====
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| − | | |
| − | ==== 0x07: SCC/SCC+ ====
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| − | Activate SCC to be accessed through memory area from 9800h to 9FFFh (4 KB mirrored)
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| − | Any bank number is valid, but bank #4 is recommanded for NEO-8 and #2 for NEO-16 to use standard address for
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| − | | |
| − | {| class="wikitable"
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| − | ! 8 || 7 || 6 || 5 || 4 || 3 || 2 || 1
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| − | |-
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| − | |style="background-color:#AAF;"| C
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |style="background-color:#BBB;"| 0
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| − | |}
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| − | | |
| − | == Appendix ==
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| − | === Programmable processor and emulation ===
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| − | Here is a pseudo code in C to handle NEO mappers extension for programmable processor based cartridges or for emulators:
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| − | | |
| − | NEO-16 mapper:
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| − | <syntaxhighlight lang="c">
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| − | const uint8* romData; // ROM data
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| − | uint16 bankValue[3]; // Bank switching register value
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| − | | |
| − | // Extended function prototypes
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| − | typedef void (*funcEnable_t)(bool, uint8);
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| − | typedef void (*funcWrite_t)(uint16, uint8);
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| − | typedef uint8 (*funcRead_t)(uint16);
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| − | // Extended functions table
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| − | funcEnable_t funcEnableTable[32];
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| − | funcWrite_t funcWriteTable[3];
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| − | funcRead_t funcReadTable[3];
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| − | | |
| − | // Handle device initialization | |
| − | void NEO16_Init()
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| − | {
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| − | for (uint8 i = 0; i < 3; i++)
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| − | {
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| − | bankValue[i] = 0x0000;
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| − | funcWriteTable[i] = NULL;
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| − | funcReadTable[i] = NULL;
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| − | }
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| − | for (uint8 i = 0; i < 32; i++)
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| − | funcEnableTable[i] = NULL;
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| − | }
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| − | | |
| − | // Handle write access
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| − | void NEO16_Write(uint16 address, uint8 value)
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| − | {
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| − | uint8 bank = ((address >> 12) & 0x03) - 1; // Get the corresponding bank number
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| − | if (bank > 2)
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| − | return; // skip
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| − | | |
| − | if (funcWriteTable[bank] != NULL) // Check for bank write callback
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| − | {
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| − | funcWriteTable[bank](address, value);
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| − | }
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| − | else if ((address & 0x0001) && (value & 0x80)) // Handle extended function
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| − | {
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| − | uint8 funcId = value & 0x3F; // Get function ID
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| − | if (funcEnableTable[funcId] != NULL)
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| − | funcEnableTable[funcId](value & 0x40, (address >> 1) & 0xFF); // Execute function specific code
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| − | }
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| − | else // Write to the given bank register
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| − | {
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| − | if (address & 1) // Set bank register MSB
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| − | bankValue[bank] = ((value & 0x0F) << 8) | (bankValue[bank] & 0x00FF);
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| − | else // Set bank register LSB
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| − | bankValue[bank] = (bankValue[bank] & 0xFF00) | (value);
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| − | }
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| − | }
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| − | | |
| − | // Handle read access
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| − | uint8 NEO16_Read(uint16 address)
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| − | {
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| − | uint8 bank = address >> 14; // Get the corresponding bank number
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| − | if (bank > 2)
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| − | return 0xFF; // skip
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| − | | |
| − | if (funcReadTable[bank] != NULL) // Check for bank read callback
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| − | return funcReadTable[bank](address);
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| − | else
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| − | return romData[(bankValue[bank]) << 14 + (address & 0x3FFF)];
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| − | }
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| − | </syntaxhighlight>
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| − | | |
| − | === Extension example ===
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| − | Here is a pseudo code in C to handle a SRAM extension for NEO mapper:
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| − | | |
| − | <syntaxhighlight lang="c">
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| − | uint8 sramSeg; // Current SRAM segment [0:15]
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| − | uint8 sramBank; // Current bank where SRAM is selected (0xFF if not selected)
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| − | uint8* sramData; // SRAM data (hardware specific)
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| − | | |
| − | // Write to SRAM
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| − | void SRAM_Write(uint16 address, uint8 value)
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| − | {
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| − | sramData[(sramSeg * 0x2000) + (address & 0x1FFF)] = value; //
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| − | }
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| − | | |
| − | // Read from SRAM
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| − | uint8 SRAM_Read(uint16 address)
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| − | {
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| − | return sramData[(sramSeg * 0x2000) + (address & 0x1FFF)];
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| − | }
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| − | | |
| − | // Enable/disable SRAM feature
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| − | void SRAM_Enable(bool enable, uint8 param)
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| − | {
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| − | if (sramBank != 0xFF) // Disable previous SRAM registration
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| − | {
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| − | if (funcWriteTable[sramBank] == SRAM_Write)
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| − | funcWriteTable[sramBank] = NULL;
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| − | if (funcReadTable[sramBank] == SRAM_Read)
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| − | funcReadTable[sramBank] = NULL;
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| − | sramBank = 0xFF;
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| − | }
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| − | | |
| − | if (enable) // Enable a SRAM segment in the given bank
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| − | {
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| − | uint8 bank = param & 0x07; // Get bank number
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| − | if (bank > 2)
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| − | return; // skip (for NEO-16)
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| − | | |
| − | sramSeg = (param >> 4) & 0x0F; // SRAM segment number
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| − | sramBank = bank;
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| − | funcWriteTable[sramBank] = SRAM_Write; // Register SRAM callbacks
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| − | funcReadTable[sramBank] = SRAM_Read;
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| − | }
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| − | }
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| − | | |
| − | // Initialize SRAM feature
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| − | void SRAM_Init()
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| − | {
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| − | sramBank = 0xFF;
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| − | funcEnableTable[0x04] = SRAM_Enable; // Register to function 0x04 (SRAM/FRAM feature)
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| − | }
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| − | </syntaxhighlight>
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| − | | |
| − | Then, you just need to call <tt>SRAM_Init()</tt> from <tt>NEO16_Init()</tt> to register the extended feature.
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