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libraw2crtc.c: add comments about CRTC 6845 registers

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This commit is contained in:
Thomas Bernard 2018-06-26 09:44:44 +02:00
parent de9d6b66d7
commit 413346b0df
1 changed files with 17 additions and 9 deletions
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26
src/libraw2crtc.c
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@ -15,16 +15,23 @@
#include "struct.h"
#include "loadsave.h"
unsigned short addrCalc(unsigned char vcc, unsigned char rcc, unsigned char hcc, unsigned char cclk, unsigned char r1, unsigned char r12, unsigned char r13)
/* 6845 registers :
* R1 : Horizontal Displayed : number of character displayed per line (4, 8 or 16 pixels depending on mode)
* R6 : Vertical Displayed : Height of displayed screen in characters
* R9 : Maximum Raster Address : number of line per character-1
* R12 : Display Start Address (High)
* R13 : Display Start Address (Low)
*/
static unsigned short addrCalc(unsigned char vcc, unsigned char rcc, unsigned char hcc, unsigned char cclk, unsigned char r1, unsigned char r12, unsigned char r13)
{
unsigned short MA;
unsigned short addr;
//MA = vcc*r1 + hcc + (0x0C)*256;
MA = vcc*r1 + hcc + r12*256 + r13;
addr = cclk | ((MA & 0x03FF) << 1);
addr = addr | ((rcc & 0x07) << 11);
addr = addr | ((MA & 0x3000) << 2);
addr = cclk | ((MA & 0x03FF) << 1); // MA9-MA0 CCLK
addr = addr | ((rcc & 0x07) << 11); // RA2-RA0 (row address)
addr = addr | ((MA & 0x3000) << 2); // MA13-MA12
return addr;
}
@ -68,9 +75,9 @@ unsigned char *raw2crtc(T_IO_Context *context, unsigned char mode, unsigned char
int i, y,x;
unsigned char r6;
unsigned char vcc;
unsigned char rcc;
unsigned char hcc;
unsigned char vcc; // vertical character count
unsigned char rcc; // raster count (line within character)
unsigned char hcc; // horizontal character count
unsigned char cclk;
int width = context->Width;
@ -116,6 +123,7 @@ unsigned char *raw2crtc(T_IO_Context *context, unsigned char mode, unsigned char
fprintf(stderr, "failed to allocate tmpBuffer\n");
exit(4);
}
memset(tmpBuffer, 0, 0x10000);
allocationBuffer = (unsigned char*)malloc(0x10000);
if(allocationBuffer == NULL)
@ -123,13 +131,13 @@ unsigned char *raw2crtc(T_IO_Context *context, unsigned char mode, unsigned char
fprintf(stderr, "failed to allocate allocationBuffer\n");
exit(4);
}
memset(allocationBuffer, 0, 0xFFFF);
memset(allocationBuffer, 0, 0x10000);
r6 = height/(r9+1);
for(vcc = 0; vcc < r6; vcc++)
{
for(rcc = 0; rcc < (r9+1); rcc++)
for(rcc = 0; rcc <= r9; rcc++)
{
for(hcc = 0; hcc < *r1; hcc++)
{