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[HAL][FREELDR] Fix system timer oscillator frequency on a Xbox (#2245)

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See https://xboxdevwiki.net/Porting_an_Operating_System_to_the_Xbox_HOWTO#Timer_Frequency
This commit is contained in:
disean 2020-01-14 23:47:36 +06:00 committed by Hermès BÉLUSCA - MAÏTO
parent 7c93350e05
commit e5c0052466
2 changed files with 15 additions and 2 deletions
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7
boot/freeldr/freeldr/arch/i386/hardware.c
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@ -27,8 +27,13 @@ DBG_DEFAULT_CHANNEL(HWDETECT);
#define MILLISEC (10)
#define PRECISION (8)
#if defined(SARCH_XBOX)
#define CLOCK_TICK_RATE 1125000
#else
#define CLOCK_TICK_RATE 1193182
#endif
#define HZ (100)
#define CLOCK_TICK_RATE (1193182)
#define LATCH (CLOCK_TICK_RATE / HZ)
static unsigned int delay_count = 1;

10
hal/halx86/include/halp.h
View file

@ -86,11 +86,18 @@ VOID
//
#define GRAPHICS_MODE_12 0x12 /* 80x30 8x16 640x480 16/256K */
#if defined(SARCH_XBOX)
//
// For some unknown reason the PIT of the Xbox is fixed at 1.125000 MHz,
// which is ~5.7% lower than on the PC.
//
#define PIT_FREQUENCY 1125000
#else
//
// Commonly stated as being 1.19318MHz
//
// See ISA System Architecture 3rd Edition (Tom Shanley, Don Anderson, John Swindle)
// P. 471
// p. 471
//
// However, the true value is closer to 1.19318181[...]81MHz since this is 1/3rd
// of the NTSC color subcarrier frequency which runs at 3.57954545[...]45MHz.
@ -104,6 +111,7 @@ VOID
// number is quite long.
//
#define PIT_FREQUENCY 1193182
#endif
//
// These ports are controlled by the i8254 Programmable Interrupt Timer (PIT)