GABE
Contents
GABE -- The System Control, I/O, and Sound Chip
"GABE" is the name of the system controller chip of the C256 Foenix RevC board, and performs several functions including system bus management, math coprocessing, I/O, and sound. The RevB version of the C256 had two chips "Gavin" and "Beatrix" that were combined into a single master chip called "GABE".
GABE has several key functions:
- System start up
- Debug interface control and bus mastering
- I/O interfacing
- Math coprocessor
- Sound chip interfacing and emulation
GABE System Startup Process
When the C256 Foenix powers up, GABE takes control and coordinates the startup process. It first copies the flash data out of flash and into system RAM, starting at bank $38 on the FMX ($18 on the RevB). GABE also copies the first bank of flash data down to bank $00 of system RAM before control is given to the CPU and the CPU's RESET is triggered. This process ensures that the kernel, hardware vectors, and interrupt handlers are all in place prior to the CPU taking control and resetting the first time on power up.
The mapping of flash memory locations to system RAM is thus:
| Flash Range | RAM Range |
|---|---|
| $F8:0000...$FF:FFFF | $38:0000...$3F:FFFF |
| $F8:0000...$F8:FFFF | $00:0000...$00:FFFF |
GABE Integer Math Coprocessor
GABE provides an easy to use integer math coprocessor in the form of two 16-multipliers (one signed, one unsigned), two 16-bit dividers (one signed, one unsigned), and a single 32-bit adder. Using the coprocessor is straight-forward: the operands are written to the correct registers, and the result is read from the output registers. The operations are all performed within a single CPU clock cycle, so no waiting is required.
| Start Address | End Address | Register Name | Additional Info |
|---|---|---|---|
| $00:0100 | $00:0101 | UNSIGNED_MULT_A | A operand for unsigned multiplication (16-bit) |
| $00:0102 | $00:0103 | UNSIGNED_MULT_B | B operand for unsigned multiplication (16-bit) |
| $00:0104 | $00:0107 | UNSIGNED_MULT_RESULT | Result for unsigned multiplication (32-bit) |
| $00:0108 | $00:0109 | SIGNED_MULT_A | A operand for signed multiplication (16-bit) |
| $00:010A | $00:010B | SIGNED_MULT_B | B operand for signed multiplication (16-bit) |
| $00:010C | $00:010F | SIGNED_MULT_RESULT | Result for signed multiplication (32-bit) |
| $00:0110 | $00:0111 | UNSIGNED_DIV_DEM | Denominator for unsigned division (16-bit) |
| $00:0112 | $00:0113 | UNSIGNED_DIV_NUM | Numerator for unsigned division (16-bit) |
| $00:0114 | $00:0115 | UNSIGNED_DIV_QUO | Quotient for unsigned division (16-bit) |
| $00:0116 | $00:0117 | UNSIGNED_DIV_REM | Remainder for unsigned division (16-bit) |
| $00:0118 | $00:0119 | SIGNED_DIV_DEM | Denominator for signed division (16-bit) |
| $00:011A | $00:011B | SIGNED_DIV_NUM | Numerator for signed division (16-bit) |
| $00:011C | $00:011D | SIGNED_DIV_QUO | Quotient for signed division (16-bit) |
| $00:011E | $00:011F | SIGNED_DIV_REM | Remainder for signed division (16-bit) |
| $00:0120 | $00:0123 | ADDER32_A | A operand for 32-bit addition (32-bits) |
| $00:0124 | $00:0127 | ADDER32_B | B operand for 32-bit addition (32-bits) |
| $00:0128 | $00:012B | ADDER32_R | Result of 32-bit addition (32-bits) |
GABE Interrupt Control Registers
There are four types of interrupt control register that GABE provides: pending, polarity, edge detection, and mask. Each interrupt that is supported has a bit position in each of the 24 or 32 bits provided by the register types.
- Pending
- The pending registers indicate if an interrupt of a particular type has been triggered and needs processing. An interrupt handler should also write to this register to clear the pending flag, once the interrupt has been processed.
- Polarity
- This register indicates if the interrupt is triggered by a high or low signal on the input to GABE.
- Edge
- This register indicates if the interrupt is triggered by an transition (edge) or by a high or low value.
- Mask
- This register indicates if the associated interrupt will trigger an IRQ to the processor. Interrupt signals with a mask bit of 0 will be ignored, while those with a mask bit of 1 will trigger an interrupt to the CPU.
| Start | Register Description | Additional Info |
|---|---|---|
| $00:0140 | INT_PENDING_REG0 | Interrupt pending #0 |
| $00:0141 | INT_PENDING_REG1 | Interrupt pending #1 |
| $00:0142 | INT_PENDING_REG2 | Interrupt pending #2 |
| $00:0143 | INT_PENDING_REG3 | Interrupt pending #3---FMX Model only |
| $00:0144 | INT_POL_REG0 | Interrupt polarity #0 |
| $00:0145 | INT_POL_REG1 | Interrupt polarity #1 |
| $00:0146 | INT_POL_REG2 | Interrupt polarity #2 |
| $00:0147 | INT_POL_REG3 | Interrupt polarity #3---FMX Model only |
| $00:0148 | INT_EDGE_REG0 | Enable Edge Detection #0 |
| $00:0149 | INT_EDGE_REG1 | Enable Edge Detection #1 |
| $00:014A | INT_EDGE_REG2 | Enable Edge Detection #2 |
| $00:014B | INT_EDGE_REG3 | Enable Edge Detection #3---FMX Model only |
| $00:0148 | INT_MASK_REG0 | Enable Interrupt #0 |
| $00:0149 | INT_MASK_REG1 | Enable Interrupt #1 |
| $00:014A | INT_MASK_REG2 | Enable Interrupt #2 |
| $00:014B | INT_MASK_REG3 | Enable Interrupt #3---FMX Model only |
There are several interrupts the GABE can handle, distributed over four blocks:
| Block | Bit | Name | Function |
|---|---|---|---|
| 0 | $01 | FNX0_INT00_SOF | Start of Frame @60Hz |
| 0 | $02 | FNX0_INT01_SOL | Start of Line (programmable) |
| 0 | $04 | FNX0_INT02_TMR0 | Timer 0 |
| 0 | $08 | FNX0_INT03_TMR1 | Timer 1 |
| 0 | $10 | FNX0_INT04_TMR2 | Timer 2 |
| 0 | $20 | FNX0_INT05_RTC | Real Time Clock |
| 0 | $40 | FNX0_INT06_FCC | Floppy Drive Controller |
| 0 | $80 | FNX0_INT07_MOUSE | Mouse Interrupt (INT12 in SuperIO IOspace) |
| 1 | $01 | FNX1_INT00_KBD | Keyboard Interrupt |
| 1 | $02 | FNX1_INT01_SC0 | VICKY_II (INT2) Sprite 2 Sprite Collision |
| 1 | $04 | FNX1_INT02_SC1 | VICKY_II (INT3) Sprite 2 Tiles Collision |
| 1 | $08 | FNX1_INT03_COM2 | Serial Port 2 (Internal) |
| 1 | $10 | FNX1_INT04_COM1 | Serial Port 1 (External) |
| 1 | $20 | FNX1_INT05_MPU401 | Midi Controller Interrupt |
| 1 | $40 | FNX1_INT06_LPT | Parallel Port |
| 1 | $80 | FNX1_INT07_SDCARD | SD Card Controller Interrupt (CH376S, if present) |
| 2 | $01 | FNX2_INT00_OPL3 | OPL3 |
| 2 | $02 | FNX2_INT01_GABE_INT0 | GABE (INT0) - TBD |
| 2 | $04 | FNX2_INT02_GABE_INT1 | GABE (INT1) - TBD |
| 2 | $08 | FNX2_INT03_SDMA | VICKY_II (INT4) |
| 2 | $10 | FNX2_INT04_VDMA | VICKY_II (INT5) -- Vicky DMA completion |
| 2 | $20 | FNX2_INT05_GABE_INT2 | GABE (INT2) - TBD |
| 2 | $40 | FNX2_INT06_EXT | External Expansion |
| 2 | $80 | FNX2_INT07_SDCARD_INS | SDCARD Insertion |
| 3 | $01 | FNX3_INT00_OPN2 | OPN2 |
| 3 | $02 | FNX3_INT01_OPM | OPM |
| 3 | $04 | FNX3_INT02_IDE | HDD IDE Interrupt |
| 3 | $08 | FNX3_INT03_TBD | TBD |
| 3 | $10 | FNX3_INT04_TBD | TBD |
| 3 | $20 | FNX3_INT05_TBD | TBD |
| 3 | $40 | FNX3_INT06_TBD | TBD |
| 3 | $80 | FNX3_INT07_TBD | TBD |
GABE Control Registers
| Start Address | Ending Address | Register Description | Additional Info |
|---|---|---|---|
| $AF:E880 | GABE_MSTR_CTRL | ||
| $AF:E881 | Reserved | ||
| $AF:E882 | GABE_RST_AUTH0 | Must Contain the BYTE $AD for Reset to Activate | |
| $AF:E883 | GABE_RST_AUTH1 | Must Contain the BYTE $DE for Reset to Activate | |
| $AF:E884 | $AF:E885 | GABE_RNG_DATASEED | On read: 16-bit random data. On write, set 16-bit RNG seed. |
| $AF:E886 | GABE_RNG_STATCTRL | On read: 8-bit status. On write: 8-bit control | |
| $AF:E887 | GABE_SYS_STAT | 8-bit system status |
GABE Master Control Register ($AF:E880)
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|
| GABE_CTRL_WRM_RST | GABE_CTRL_BUZZER | GABE_CTRL_SDC_LED | GABE_CTRL_PWR_LED |
- GABE_CTRL_PWR_LED
- Turns the power LED (next to the reset button) on or off.
- GABE_CTRL_SDC_LED
- Turns the SDC activity LED (next to the SDC slot) on or off.
- GABE_CTRL_BUZZER
- Turns the built-in piezo buzzer on or off.
- GABE_CTRL_WRM_RST
- Triggers a warm reset of the board (GABE_RST_AUTH0 must be set to $AD and GABE_RST_AUTH1 to $DE in order to trigger the reset).
GABE System Status Register ($AF:E887)
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|
| GABE_SYS_STAT_CPUX | GABE_SYS_STAT_CPUA | GABE_SYS_STAT_EXP | GABE_SYS_STAT_MID1 | GABE_SYS_STAT_MID0 |
- GABE_SYS_STAT_CPUX
- Indicates if the CPU's index registers are 8-bits or 16-bits wide.
- GABE_SYS_STAT_CPUA
- Indicates if the CPU's accumulator is 8-bits or 16-bits wide.
- GABE_SYS_STAT_EXP
- Indicates if the and expansion card is present (0).
- GABE_SYS_STAT_MID1 and GABE_SYS_STAT_MID0
- These two bits show the machine ID:
| GABE_SYS_STAT_MID1 | GABE_SYS_STAT_MID0 | Machine |
|---|---|---|
| 0 | 0 | FMX - Development Platform |
| 0 | 1 | C256 Foenix - Dev Platform |
| 1 | 0 | C256 Foenix - User Version (65C816) |
| 1 | 1 | Reserved |
