| Rev |
Log message |
Author |
Age |
Path |
| 223 |
Added an OPEN8_BUS_TYPE record to simplify connection to Open8 modules. The CPU now passes and Open8_Bus out, which supplies the bus address, write enable, write data, and read enable. Read data and interrupts are still handled as separate signals, since they are muxed/connected at the next level up. |
jshamlet |
1513d 15h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 210 |
Modified the timers to reset on new interval write. This avoids an issue in the original design where the timer had to reach zero before updating, potentially causing unwanted interrupts.
Also added a flag to the CPU to allow interrupts to be processed sequentially based on the state of the I bit. This one is set to false by default, as it is a significant change in interrupt behavior. Long, and reentrant, ISRs can clear the I bit prematurely to allow themselves to be interrupted.
Lastly, added the I bit to the exported flags for possible use in memory protection schemes. |
jshamlet |
1519d 23h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 209 |
Fixed an issue in the PIT timer that caused an immediate interrupt on interval write,
Fixed an issue in the epoch timer that resulted in a spurious interrupt due to extra LSB's being set by default in the set point register,
While cleaning elsewhere, founding a spacing issue in the CPU HDL,
Added a 4k ROM and MW core. |
jshamlet |
1520d 12h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 194 |
Cleaned up licensing sections |
jshamlet |
1528d 18h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 191 |
Cleaned up comments, added back the OPEN8_NULLBUS constant, and added some new modules for ADCs and LCD displays.
Also made the button input module more configurable by moving the debounce code to a separate entity and using generics to instantiate it. |
jshamlet |
1528d 18h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 190 |
Fixed a bug in CPU where RTI/RTS wasn't idling the instruction cache, causing intermittent failures where RTI would execute as RTS, corrupting the stack;
Fixed a bug in the real-time clock where the uSec tick generator would stop if the PIT timer value was left/set to 0x00. |
jshamlet |
1540d 16h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 188 |
Added a generic to alter the behavior of RTI so that it can optionally skip restoring the general purpose flags GP4 to GP7, allowing ISR's to make persistent changes to them. Also exported these flags to the top level for use outside the CPU. |
jshamlet |
1541d 19h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 187 |
Added the CPU_Halt input, only now as an input to the instruction decoder. The CPU_Halt line will assert the registered CPU_Halt_Req, which will cause the instruction decoder to abort the current instruction, reset the PC, then enter a hold state until the line is deasserted. Additionally, a very minor bug that could cause the SMSK instruction to effectively execute twice if interrupted was fixed. Lastly, cleaned up the comments even more. |
jshamlet |
1543d 16h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 186 |
Merged the interrupt override logic into the case structure, simplifying how interrupts are processed. |
jshamlet |
1546d 15h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 185 |
1) Fixed an apparently long-standing bug where the interrupt bit wasn't being cleared after an RTI
2) Modified the program counter logic to be simpler. It now always increments, and states control the increment using the offset field. A new set of constants was added to replace the old states.
3) Modified the ALU to always use Operand1 instead of ALU_Ctrl.Data (and removed the field in the record). A new ALU command, ALU_GMSK, was added, as it was the only instruction to set the .Data field to something other than Operand1 (Int_Mask)
4) Modified the package file so that flag names match what the assembler calls them. FL_Z is now PSR_Z, FL_GP1 is now PSR_GP4, etc.
5) Cleaned up the comments and code formatting |
jshamlet |
1546d 18h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 183 |
Renamed core to o8_cpu to match new naming scheme |
jshamlet |
1548d 18h |
/open8_urisc/trunk/VHDL/o8_cpu.vhd |
| 182 |
Simplified the address generation logic at the expense of making LDX take one additional clock cycle. This allowed the address logic to be split out of the main state machine and simplified (greatly). During this process, a bug in SDO was found and fixed that caused it to return through the wrong pipe fill state wnen auto increment was disabled. |
jshamlet |
1548d 18h |
/open8_urisc/trunk/VHDL/Open8.vhd |
| 181 |
Altered the RSP instruction to allow the stack pointed to either be restored from registers or stored to registers based on the status of a processor bit. Also modified LDX to simplify the address logic. |
jshamlet |
1549d 15h |
/open8_urisc/trunk/VHDL/Open8.vhd |
| 172 |
General code cleanup |
jshamlet |
3073d 16h |
/open8_urisc/trunk/VHDL/Open8.vhd |
| 169 |
Corrected issue with CMP and SBC generating an inverted carry flag and added new constants to the package file to simplify interfacing new modules. |
jshamlet |
3128d 17h |
/open8_urisc/trunk/VHDL/Open8.vhd |
| 168 |
Simplified write data path logic,
Converted RTC to packed BCD,
Corrected several bugs in real time clock component, |
jshamlet |
3907d 13h |
/open8_urisc/trunk/VHDL/Open8.vhd |
| 167 |
Updated CPU model; Pipelined ALU control signals to improve fMAX, corrected issue with interrupt controller priority not being obeyed, fixed bug in auto-indexing instructions where the upper register wasn't being properly incremented, cleaned up code to make the processor model easier to follow.
Added several useful modules that use the Open8 bus. |
jshamlet |
3915d 12h |
/open8_urisc/trunk/VHDL/Open8.vhd |
| 164 |
Modified the data path to allow the bus to go idle while waiting for an interrupt. This makes it easier to debug code that uses the WAI instruction, as both Wr_Enable and Rd_Enable go low. |
jshamlet |
4551d 07h |
/open8_urisc/trunk/VHDL/Open8.vhd |
| 162 |
Added optional generic to specify that the BRK instruction implements a WAit_for_Interrupt (WAI) instruction instead. Logically emulates INT, but without triggering a soft interrupt. Note that the NOP instruction maps to BRK, and will not function correctly if this option is set. |
jshamlet |
4642d 00h |
/open8_urisc/trunk/VHDL/Open8.vhd |
| 156 |
Optimized for timing,
Flattened block structure to single entity. |
jshamlet |
4698d 15h |
/open8_urisc/trunk/VHDL/Open8.vhd |
