cpct_setPalette

Changes the hardware palette colour values (selecting new ones).

C Definition

void cpct_setPalette (u8* colour_array, u16 size)

Input Parameters (4 Bytes)

Assembly call (Input parameters on registers)

call cpct_setPalette_asm

Parameter Restrictions

• colour_array must be an array of unsigned 8-bit values (u8), each one in the [0-31] range.
• size must be between 1 and 16.  A size of 0 will be treated as 256, and any value greater than 16 will cause undefined behaviour, probably leading to program crashes.

Requirements

This function requires the CPC firmware to be DISABLED.  Otherwise, it may not work, as firmware tends to restore palette colour values to its own selection.

Details

This function modifies hardware palette registers to set new colours to use.  These colours values are easily identified with PENs on the CPC, and are the ones shown in the 2nd column of Table 1.  The function starts modiying PEN 0, and goes changing PEN 1, 2, 3... up to the number of provided colours (size) from the colour_array.  It is important to notice that this function requires hardware colour values, which are different from firmware colour values (usually known as INKs on the CPC).  Table 1 shows all of them, and you may use it for reference.

Palette registers are contained inside the PAL chip of the CPC (which is located inside the Gate Array).  To access PAL chip, the same port (&7F) as Gate Array is used.  The function is not thought to be optimal, but secure.  If a more optimal one is required, it can be derived from this code.  The array of color values passed to this routine must include hardware color values (0-31) and not firmware ones.

Firmware | Hardware  | Hard+Command | Colour Name    |  R%   G%   B% Colour
---------------------------------------------------------------------------
     0   | 20 (0x14) |  0x54        | Black          |   0    0    0
     1   |  4 (0x04) |  0x44 (0x50) | Blue           |   0    0   50
     2   | 21 (0x15) |  0x55        | Bright Blue    |   0    0  100
     3   | 28 (0x1C) |  0x5C        | Red            |  50    0    0
     4   | 24 (0x18) |  0x58        | Magenta        |  50    0   50
     5   | 29 (0x1D) |  0x5D        | Mauve          |  50    0  100
     6   | 12 (0x0C) |  0x4C        | Bright Red     | 100    0    0
     7   |  5 (0x05) |  0x45 (0x48) | Purple         | 100    0   50
     8   | 13 (0x0D) |  0x4D        | Bright Magenta | 100    0  100
     9   | 22 (0x16) |  0x56        | Green          |   0   50    0
    10   |  6 (0x06) |  0x46        | Cyan           |   0   50   50
    11   | 23 (0x17) |  0x57        | Sky Blue       |   0   50  100
    12   | 30 (0x1E) |  0x5E        | Yellow         |  50   50    0
    13   |  0 (0x00) |  0x40 (0x41) | White          |  50   50   50
    14   | 31 (0x1F) |  0x5F        | Pastel Blue    |  50   50  100
    15   | 14 (0x0E) |  0x4E        | Orange         | 100   50    0
    16   |  7 (0x07) |  0x47        | Pink           | 100   50   50
    17   | 15 (0x0F) |  0x4F        | Pastel Magenta | 100   50  100
    18   | 18 (0x12) |  0x52        | Bright Green   |   0  100    0
    19   |  2 (0x02) |  0x42 (0x51) | Sea Green      |   0  100   50
    20   | 19 (0x13) |  0x53        | Bright Cyan    |   0  100  100
    21   | 26 (0x1A) |  0x5A        | Lime           |  50  100    0
    22   | 25 (0x19) |  0x59        | Pastel Green   |  50  100   50
    23   | 27 (0x1B) |  0x5B        | Pastel Cyan    |  50  100  100
    24   | 10 (0x0A) |  0x4A        | Bright Yellow  | 100  100    0
    25   |  3 (0x03) |  0x43 (0x49) | Pastel Yellow  | 100  100   50
    26   | 11 (0x0B) |  0x4B        | Bright White   | 100  100  100
---------------------------------------------------------------------------
   Table 1. Colour values on the CPC (Firmware, Hardware and RGB)

Table 1 shows Firmware colour values (column 1), Hardware correspondant colour values (column 2) and classic Hardware values (column 3) which include the colour value (5 Least significant bits) along with the command for the Gate Array (3 Most significant bits).  As this function already provides hardware commands, the values it requires are the ones from column 2 (Hardware).  Table 1 also provides colour names and precentages of RGB values for better understanding.

Known limitations

This function cannot set blinking colors, as blinking colours are managed by the firmware (not by hardware).

Destroyed Register values

AF, BC, DE, HL

Required memory

Time Measures

   Case    | microSecs (us) | CPU Cycles
---------------------------------------------
    Any    |   22 + 20*NC   |  88 + 80*NC
---------------------------------------------
Asm saving |      -13       |    -52
---------------------------------------------
NC =  4    |      102       |    408
NC = 16    |      342       |   1368

NC=Number of colours to be set

Credits

This function has been constructed with great help from the documentation at Grimware about the Gate Array.

http://www.grimware.org/doku.php/documentations/devices/gatearray