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Improvements in README.md

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Clifford Wolf 2015-06-25 14:11:42 +02:00
parent 23b700cf73
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README.md
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@ -53,7 +53,7 @@ Parameters:
The following Verilog module parameters can be used to configure the PicoRV32 The following Verilog module parameters can be used to configure the PicoRV32
core. core.
### ENABLE_COUNTERS (default = 1) #### ENABLE_COUNTERS (default = 1)
This parameter enables support for the `RDCYCLE[H]`, `RDTIME[H]`, and This parameter enables support for the `RDCYCLE[H]`, `RDTIME[H]`, and
`RDINSTRET[H]` instructions. This instructions will cause a hardware `RDINSTRET[H]` instructions. This instructions will cause a hardware
@ -64,43 +64,43 @@ instructions are not optional for an RV32I core. But chances are they are not
going to be missed after the application code has been debugged and profiled. going to be missed after the application code has been debugged and profiled.
This instructions are optional for an RV32E core.* This instructions are optional for an RV32E core.*
### ENABLE_REGS_16_31 (default = 1) #### ENABLE_REGS_16_31 (default = 1)
This parameter enables support for registers the `x16`..`x31`. The RV32E ISA This parameter enables support for registers the `x16`..`x31`. The RV32E ISA
excludes this registers. However, the RV32E ISA spec requires a hardware trap excludes this registers. However, the RV32E ISA spec requires a hardware trap
for when code tries to access this registers. This is not implemented in PicoRV32. for when code tries to access this registers. This is not implemented in PicoRV32.
### ENABLE_REGS_DUALPORT (default = 1) #### ENABLE_REGS_DUALPORT (default = 1)
The register file can be implemented with two or one read ports. A dual ported The register file can be implemented with two or one read ports. A dual ported
register file improves performance a bit, but can also increase the size of register file improves performance a bit, but can also increase the size of
the core. the core.
### LATCHED_MEM_RDATA (default = 0) #### LATCHED_MEM_RDATA (default = 0)
Set this to 1 if the `mem_rdata` is kept stable by the external circuit after a Set this to 1 if the `mem_rdata` is kept stable by the external circuit after a
transaction. In the default configuration the PicoRV32 core only expects the transaction. In the default configuration the PicoRV32 core only expects the
`mem_rdata` input to be valid in the cycle with `mem_valid && mem_ready` and `mem_rdata` input to be valid in the cycle with `mem_valid && mem_ready` and
latches the value internally. latches the value internally.
### ENABLE_EXTERNAL_IRQ (default = 0) #### ENABLE_EXTERNAL_IRQ (default = 0)
Set this to 1 to enable external IRQs. Set this to 1 to enable external IRQs.
### ENABLE_ILLINSTR_IRQ (default = 0) #### ENABLE_ILLINSTR_IRQ (default = 0)
Set this to 1 to enable the illigal instruction IRQ. This can be used for Set this to 1 to enable the illegal instruction IRQ. This can be used for
software implementations of instructions such as `MUL` and `DIV`. software implementations of instructions such as `MUL` and `DIV`.
### ENABLE_TIMER_IRQ (default = 0) #### ENABLE_TIMER_IRQ (default = 0)
Set this to 1 to enable the built-in timer and timer IRQ. Set this to 1 to enable the built-in timer and timer IRQ.
### PROGADDR_RESET (default = 0) #### PROGADDR_RESET (default = 0)
The start address of the program. The start address of the program.
### PROGADDR_IRQ (default = 16) #### PROGADDR_IRQ (default = 16)
The start address of the interrupt handler. The start address of the interrupt handler.
@ -136,17 +136,16 @@ Dhrystone benchmark results: 0.309 DMIPS/MHz (544 Dhrystones/Second/MHz)
For the Dhrystone benchmark the average CPI is 4.167. For the Dhrystone benchmark the average CPI is 4.167.
Custom Instructions: Custom Instructions for IRQ Handling
-------------------- ------------------------------------
### IRQ Handling
The following custom instructions are supported when IRQs are enabled. The following custom instructions are supported when IRQs are enabled.
The core has 4 additional 32-bit general-purpose registers `q0 .. q3` The core has 4 additional 32-bit registers `q0 .. q3` that are used for IRQ
that are used for IRQ handling. When an IRQ triggers, the register handling. When an IRQ triggers, the register `q0` contains the return address
`q0` contains the return address and `q1` contains the IRQ number. and `q1` contains the IRQ number. Registers `q2` and `q3` are uninitialized
Registers `q2` and `q3` are uninitialized. and can be used as temporary storage when saving/restoring register values
in the IRQ handler.
#### getq rd, qs #### getq rd, qs
@ -156,7 +155,7 @@ register. The Instruction is encoded under the `custom0` opcode:
0000000 00000 000XX 000 XXXXX 0001011 0000000 00000 000XX 000 XXXXX 0001011
f7 f5 qs f3 rd opcode f7 f5 qs f3 rd opcode
Example assember code using the `custom0` mnemonic: Example assembler code using the `custom0` mnemonic:
| Instruction | Assember Code | | Instruction | Assember Code |
| ------------------| --------------------| | ------------------| --------------------|
@ -172,7 +171,7 @@ q-register. The Instruction is encoded under the `custom0` opcode:
0000001 00000 XXXXX 000 000XX 0001011 0000001 00000 XXXXX 000 000XX 0001011
f7 f5 rs f3 qd opcode f7 f5 rs f3 qd opcode
Example assember code using the `custom0` mnemonic: Example assembler code using the `custom0` mnemonic:
| Instruction | Assember Code | | Instruction | Assember Code |
| ------------------| --------------------| | ------------------| --------------------|
@ -189,7 +188,7 @@ encoded under the `custom0` opcode:
0000010 00000 00000 000 00000 0001011 0000010 00000 00000 000 00000 0001011
f7 f5 rs f3 rd opcode f7 f5 rs f3 rd opcode
Example assember code using the `custom0` mnemonic: Example assembler code using the `custom0` mnemonic:
| Instruction | Assember Code | | Instruction | Assember Code |
| ------------------| --------------------| | ------------------| --------------------|
@ -216,7 +215,7 @@ in the `f5` field:
Set bits in the IRQ mask correspond to enabled interrupt sources. Set bits in the IRQ mask correspond to enabled interrupt sources.
Example assember code using the `custom0` mnemonic: Example assembler code using the `custom0` mnemonic:
| Instruction | Assember Code | | Instruction | Assember Code |
| ------------------| --------------------| | ------------------| --------------------|
@ -236,7 +235,7 @@ Pause execution until an interrupt triggers. The Instruction is encoded under th
0000100 00000 00000 000 00000 0001011 0000100 00000 00000 000 00000 0001011
f7 f5 rs f3 rd opcode f7 f5 rs f3 rd opcode
Example assember code using the `custom0` mnemonic: Example assembler code using the `custom0` mnemonic:
| Instruction | Assember Code | | Instruction | Assember Code |
| ------------------| --------------------| | ------------------| --------------------|
@ -251,7 +250,7 @@ counter to zero disables the timer.
0000101 00000 XXXXX 000 00000 0001011 0000101 00000 XXXXX 000 00000 0001011
f7 f5 rs f3 rd opcode f7 f5 rs f3 rd opcode
Example assember code using the `custom0` mnemonic: Example assembler code using the `custom0` mnemonic:
| Instruction | Assember Code | | Instruction | Assember Code |
| ------------------| --------------------| | ------------------| --------------------|