Difference between revisions of "NEX file format"

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(V1.3 extensions proposal added)
 
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The NEX file format was designed as very simple and straightforward format to load self-contained applications into memory and start them. Through various extensions it did reach v1.3 at this moment, which allows even for more complex use cases.
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The NEX file format was designed as very simple and straightforward format to load self-contained applications into memory and start them.  
 +
 
 +
At this time the official Distro supported version is the V1.2 of the specification.
  
 
The official distribution sports some goodies for NEX files:
 
The official distribution sports some goodies for NEX files:
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* [https://github.com/Threetwosevensixseven/NexCreator/tree/master/nexload SevenFFF's fork of NexCreator and nexload]
 
* [https://github.com/Threetwosevensixseven/NexCreator/tree/master/nexload SevenFFF's fork of NexCreator and nexload]
 
* [https://github.com/varmfskii/zxnext_tools Varmfskii's ZX Next tools]
 
* [https://github.com/varmfskii/zxnext_tools Varmfskii's ZX Next tools]
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* [https://github.com/ped7g/ZXSpectrumNextMisc/tree/master/nexload2 Ped's nexload2.asm] (rewritten from scratch)
 
 
* [https://github.com/z00m128/sjasmplus/releases Z00m's sjasmplus] has support for [http://z00m128.github.io/sjasmplus/documentation.html#c_savenex NEX saving] since v1.13.0
 
* [https://github.com/z00m128/sjasmplus/releases Z00m's sjasmplus] has support for [http://z00m128.github.io/sjasmplus/documentation.html#c_savenex NEX saving] since v1.13.0
  
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| style="text-align:right;" | 512 ||  || "Next" string followed by file header, containing also map of memory banks stored in the file
 
| style="text-align:right;" | 512 ||  || "Next" string followed by file header, containing also map of memory banks stored in the file
 
|-
 
|-
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| style="text-align:right;" | 512 || * || optional palette (for Layer2 or LoRes screen)
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| style="text-align:right;" | 512 || * || optional palette (for Layer2, LoRes or Tilemap screen)
 
|-
 
|-
 
| style="text-align:right;" | 49152 || * || Layer2 loading screen
 
| style="text-align:right;" | 49152 || * || Layer2 loading screen
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|-
 
|-
 
| style="text-align:right;" | 12288 || * || Timex HiCol (8x1) loading screen
 
| style="text-align:right;" | 12288 || * || Timex HiCol (8x1) loading screen
 +
|-
 +
| style="text-align:right;" | 81920 || * || Layer 2 320x256x8 or 640x256x4 loading screen
 +
|-
 +
| style="text-align:right;" | 2048 || * || Copper code for copper loading-effects
 
|-
 
|-
 
| style="text-align:right;" | n * 16384 || * || 16kiB raw memory bank data in predefined order: 5,2,0,1,3,4,6,7,8,9,10,...,111 (particular bank may be omitted completely)
 
| style="text-align:right;" | n * 16384 || * || 16kiB raw memory bank data in predefined order: 5,2,0,1,3,4,6,7,8,9,10,...,111 (particular bank may be omitted completely)
Line 44: Line 49:
 
| 0 || 4 || "Next" string
 
| 0 || 4 || "Next" string
 
|-
 
|-
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| 4 || 4 || string with NEX file version, currently "V1.0", "V1.1", "V1.2" or "V1.3"
+
| 4 || 4 || string with NEX file version, currently "V1.0", "V1.1", or "V1.2"
 
|-
 
|-
 
| 8 || 1 || RAM required: 0 = 768k, 1 = 1792k
 
| 8 || 1 || RAM required: 0 = 768k, 1 = 1792k
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| 10 || 1 || Loading-screen blocks in file (bit-flags):
 
| 10 || 1 || Loading-screen blocks in file (bit-flags):
 
128 = no palette block, 16 = Hi-Colour, 8 = Hi-Res, 4 = Lo-Res, 2 = ULA, 1 = Layer2
 
128 = no palette block, 16 = Hi-Colour, 8 = Hi-Res, 4 = Lo-Res, 2 = ULA, 1 = Layer2
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The loader does use common banks to load the graphics into, and show it from, i.e. bank5 for all ULA related modes and banks 9,10 and 11 for Layer2 graphics (loading these banks afterwards as regular bank will thus replace the shown data on screen). Only Layer2 and Lo-Res screens expect the palette block (unless +128 flag set). While one can include multiple screen data in single file (setting up all relevant bits), the recommended/expected usage is to have only one type of screen in NEX file.
+
 
 +
The loader does use common banks to load the graphics into, and show it from, i.e. bank5 for all ULA related modes and banks 9,10 and 11 for Layer2 graphics (loading these banks afterwards as regular bank will thus replace the shown data on screen).
 +
 
 +
Only Layer2, Tilemap and Lo-Res screens expect the palette block (unless +128 flag set). While one can include multiple screen data in single file (setting up all relevant bits), the recommended/expected usage is to have only one type of screen in NEX file.
 
|-
 
|-
 
| 11 || 1 || Border Colour: 0-7
 
| 11 || 1 || Border Colour: 0-7
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| 130 || 1 || Layer2 "loading bar" 0 = OFF, 1 = ON (works only in combination with Layer2 screen data)
 
| 130 || 1 || Layer2 "loading bar" 0 = OFF, 1 = ON (works only in combination with Layer2 screen data)
 
|-
 
|-
−
| 131 || 1 || "Loading bar" colour (0..255)
+
| 131 || 1 || "Loading bar" colour (0..255) (for 640x256x4 mode the byte defines pixels pair)
 
|-
 
|-
 
| 132 || 1 || Loading delay per bank (0..255 amount of frames), 0 = no delay
 
| 132 || 1 || Loading delay per bank (0..255 amount of frames), 0 = no delay
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| 133 || 1 || Start delay (0..255 amount of frames), 0 = no delay
 
| 133 || 1 || Start delay (0..255 amount of frames), 0 = no delay
 
|-
 
|-
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| 134 || 1 || Preserve current Next-Registers values (0 = reset, 1 = preserve)
+
| 134 || 1 || Preserve current Next-Registers values (0 = reset machine state, 1 = preserve)
 
|-
 
|-
 
| 135 || 3 || Required core version, three bytes 0..15 "major", 0..15 "minor", 0..255 "subminor" version numbers. (core version is checked only when reported machine-ID is 10 = "Next", on other machine or emulator=8 the latest loaders will skip the check)
 
| 135 || 3 || Required core version, three bytes 0..15 "major", 0..15 "minor", 0..255 "subminor" version numbers. (core version is checked only when reported machine-ID is 10 = "Next", on other machine or emulator=8 the latest loaders will skip the check)
 
|-
 
|-
 
| 138 || 1 || Timex HiRes 512x192 mode colour, encoded as for port 255 = bits 5-3. I.e. values 0, 8, 16, .., 56 (0..7 * 8)
 
| 138 || 1 || Timex HiRes 512x192 mode colour, encoded as for port 255 = bits 5-3. I.e. values 0, 8, 16, .., 56 (0..7 * 8)
 +
 +
When screens 320x256x8 or 640x256x4 are used, this byte is re-used as palette offset for Layer 2 mode, values 0..15
 
|-
 
|-
 
| 139 || 1 || Entry bank = bank to be mapped into slot 3 (0xC000..0xFFFF address space), the "Program Counter" (header offset +14) and "File handle address" (header offset +140) are used by NEX loader after the mapping is set (The default ZX128 has bank 0 mapped after reset, which makes zero value nice default).
 
| 139 || 1 || Entry bank = bank to be mapped into slot 3 (0xC000..0xFFFF address space), the "Program Counter" (header offset +14) and "File handle address" (header offset +140) are used by NEX loader after the mapping is set (The default ZX128 has bank 0 mapped after reset, which makes zero value nice default).
 
|-
 
|-
 
| 140 || 2 || File handle address: 0 = NEX file is closed by the loader, 1..0x3FFF values (1 recommended) = NEX loader keeps NEX file open and does pass the file handle in BC register, 0x4000..0xFFFF values (for 0xC000..0xFFFF see also "Entry bank") = NEX loader keeps NEX file open and the file handle is written into memory at the desired address.
 
| 140 || 2 || File handle address: 0 = NEX file is closed by the loader, 1..0x3FFF values (1 recommended) = NEX loader keeps NEX file open and does pass the file handle in BC register, 0x4000..0xFFFF values (for 0xC000..0xFFFF see also "Entry bank") = NEX loader keeps NEX file open and the file handle is written into memory at the desired address.
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|-
 
−
| 142 || 1 || (V1.3) 0 = disable Expansion Bus by setting top four bits of {{NextRegNo|$80}} to 0, 1 = do nothing (does apply only to cores 3.0.5+)
 
−
|-
 
−
| 143 || 369 || reserved for future extensions, set to zero in older versions of file format.
 
 
|}
 
|}
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The V1.3 is currently work-in-progress (so far only one new flag has been added at offset 142), and there may be more new features coming in following weeks.
 
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------------------------------
 
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Currently I (Ped7g) am considering to add these fields to the V1.3 header, feel free to comment about these on SpectrumNext discord server in #tools channel (I believe I will have prototype implementation in following days, and eventually based on the feedback this may become final V1.3 header in a week or so):
 
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Proposed further changes of the header block for V1.3:
 
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{| class="wikitable"
 
−
|-
 
−
! offset !! size !! description
 
−
|-
 
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| 143 || 1 || 1 = Has checksum value, checksum algorithm is CRC-32C (Castagnoli), value itself is at the very end of the header block
 
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|-
 
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| 144 || 4 || File offset of first bank data (when loader is parsing known version, it should know where the banks start without this value, but it may use it for extra check whether the parsing of optional blocks between header and first bank was done correctly)
 
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|-
 
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| 148 || 2 || CLI buffer address (after "Entry bank" is paged in), 0 = no buffer
 
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|-
 
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| 150 || 2 || CLI buffer size - when address and size are provided, the original command line passed to NEX loader will be copied to defined buffer (and truncated to "size", shorter string may be zero-terminated) and register DE is set to the buffer address.
 
−
|-
 
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| 152 || 1 || Loading screen flags 2 - when first flag has value 64 set (+128 no-palette is partially valid for new cases too, other bits should be not mixed with new modes):
 
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1 = Layer 2 320x256x8bpp (old +128 no-palette does apply too) blocks: 512B palette + 81920B data
 
−
2 = Layer 2 640x256x4bpp (old +128 no-palette does apply too) blocks: 512B palette + 81920B data
 
−
  (HiRes color value is used as L2 palette offset - does apply to both new Layer 2 modes)
 
−
3 = Tilemode screen, block 512B: 508B palette (254 colors only) + 4B NextRegs $6B, $6C, $6E, $6F
 
−
  Tilemap data are stored in regular bank 5 - no specialized data block is used.
 
−
For Layer 2 banks 9,10,11,12,13 are used to display the loading screen.
 
−
|-
 
−
| 153 || 355 || reserved for future extensions, set to zero in older versions of file format.
 
−
|-
 
−
| 508 || 4 || optional CRC-32C (Castagnoli) - is calculated by checksumming file content from offset 512 (after this value) till end of file (including the optional custom binary appended after regular NEX file), and then further checksumming first 508 bytes of the header (the only skipped four bytes are then this checksum value).
 
−
|}
 
−
 
−
I tried to consider also the multi-handle of NEX file feature, but I was unable to figure out implementation details how to achieve desired outcome and what are the limits and API, so it's not included in my current V1.3 proposal.
 
  
 
------------------------------
 
------------------------------
  
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Possible roadmap/ideas for future (this is just collection of ideas, no timeframe or guarantee that they will ever happen, feel free to comment on them):
+
Alternative file formats, and possible extensions to this fileformat are noted on the [[Alternative_NEX_file_formats|Alternative NEX file formats]] page, to prevent confusion with supported features in the shipping distribtion and the licensed "Retail SD Card" distribution.
−
* probably compatible with current V1.2 file format
 
−
** checking machine memory and use the RAMREQ to report low memory
 
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** having entry bank dynamically allocated by NextZXOS (entrybank = 255?)
 
−
** changing working directory if path with directories was provided (adjust that also when passing command line in V1.3 to make file-only like)
 
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* V1.3+
 
−
** passing cmd line args to the loaded code - after discussion with Allen A. => BC = file handle (or 255), DE = command line (is equal to the field buffer value in header), zero terminated string (if the zero terminator is missing, the line is probably truncated to buffer size) = two new words into V1.3 header [cliBuffer, cliSize].
 
−
** preserving original NextZXOS stack SP value (stack pointer = 2?) (0 is valid SP starting from very "top" of RAM) (preserving is risky, as there is always possibility of ramtop being set in such unfortunate manner, that preserved sp will cause destruction of the loaded code, so the SP should be set up by the header every time, but maybe there can be extra flag to put old value into the new stack by loader, so the code can eventually get to the content of old stack - if the NEX file doesn't overwrite the banks 5/2/0)
 
−
** checksums incorporated into the NEX file (maybe into header?) - mostly for file archival/transfers, not loader itself
 
−
** custom palettes also for ULA/HiRes/HiCol screens (maybe +64 flag?) (or invert the +128 in V1.3 for those three modes, i.e. 0 = no pal / 128 = has pal)
 
−
** tilemap screen
 
−
** return multiple open file handles to the .nex file. Specify how many handles and an address in the header.
 
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** With a flag (bit 7 of number of handles?) to force close all existing open handles first.
 

Latest revision as of 16:27, 1 December 2023

The NEX file format was designed as very simple and straightforward format to load self-contained applications into memory and start them.

At this time the official Distro supported version is the V1.2 of the specification.

The official distribution sports some goodies for NEX files:

Additional resources:

The basic structure of the file is:

block size optional description
512 "Next" string followed by file header, containing also map of memory banks stored in the file
512 * optional palette (for Layer2, LoRes or Tilemap screen)
49152 * Layer2 loading screen
6912 * classic ULA loading screen
12288 * LoRes loading screen
12288 * Timex HiRes (512x192) loading screen
12288 * Timex HiCol (8x1) loading screen
81920 * Layer 2 320x256x8 or 640x256x4 loading screen
2048 * Copper code for copper loading-effects
n * 16384 * 16kiB raw memory bank data in predefined order: 5,2,0,1,3,4,6,7,8,9,10,...,111 (particular bank may be omitted completely)
m * Optional binary data appended after "regular" NEX file content - custom format

Structure of the header block:

offset size description
0 4 "Next" string
4 4 string with NEX file version, currently "V1.0", "V1.1", or "V1.2"
8 1 RAM required: 0 = 768k, 1 = 1792k
9 1 Number of 16k Banks to Load: 0-112 (see also the byte array at offset 18, which must yield this count)
10 1 Loading-screen blocks in file (bit-flags):

128 = no palette block, 16 = Hi-Colour, 8 = Hi-Res, 4 = Lo-Res, 2 = ULA, 1 = Layer2

The loader does use common banks to load the graphics into, and show it from, i.e. bank5 for all ULA related modes and banks 9,10 and 11 for Layer2 graphics (loading these banks afterwards as regular bank will thus replace the shown data on screen).

Only Layer2, Tilemap and Lo-Res screens expect the palette block (unless +128 flag set). While one can include multiple screen data in single file (setting up all relevant bits), the recommended/expected usage is to have only one type of screen in NEX file.

11 1 Border Colour: 0-7
12 2 Stack pointer
14 2 Program counter (0 = don't run, just load)
16 2 "Number of extra files" (currently not used by anything/anyone?)
18 112 byte flag (0/1) of 16k banks included in the file - this array is in regular order 0..111, i.e. bank5 in file will set 1 to header byte at offset 18+5 = 23, but the 16kiB of data for bank 5 are first in the file (order of bank data in file is: 5,2,0,1,3,4,6,7,8,9,10,...,111)
130 1 Layer2 "loading bar" 0 = OFF, 1 = ON (works only in combination with Layer2 screen data)
131 1 "Loading bar" colour (0..255) (for 640x256x4 mode the byte defines pixels pair)
132 1 Loading delay per bank (0..255 amount of frames), 0 = no delay
133 1 Start delay (0..255 amount of frames), 0 = no delay
134 1 Preserve current Next-Registers values (0 = reset machine state, 1 = preserve)
135 3 Required core version, three bytes 0..15 "major", 0..15 "minor", 0..255 "subminor" version numbers. (core version is checked only when reported machine-ID is 10 = "Next", on other machine or emulator=8 the latest loaders will skip the check)
138 1 Timex HiRes 512x192 mode colour, encoded as for port 255 = bits 5-3. I.e. values 0, 8, 16, .., 56 (0..7 * 8)

When screens 320x256x8 or 640x256x4 are used, this byte is re-used as palette offset for Layer 2 mode, values 0..15

139 1 Entry bank = bank to be mapped into slot 3 (0xC000..0xFFFF address space), the "Program Counter" (header offset +14) and "File handle address" (header offset +140) are used by NEX loader after the mapping is set (The default ZX128 has bank 0 mapped after reset, which makes zero value nice default).
140 2 File handle address: 0 = NEX file is closed by the loader, 1..0x3FFF values (1 recommended) = NEX loader keeps NEX file open and does pass the file handle in BC register, 0x4000..0xFFFF values (for 0xC000..0xFFFF see also "Entry bank") = NEX loader keeps NEX file open and the file handle is written into memory at the desired address.

Alternative file formats, and possible extensions to this fileformat are noted on the Alternative NEX file formats page, to prevent confusion with supported features in the shipping distribtion and the licensed "Retail SD Card" distribution.

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