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RISC-V: Add support for RV32E extension in GCC port (FreeRTOS#543)
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Co-authored-by: Joseph Julicher <jjulicher@mac.com>
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@Limoto @n9wxu
Limoto and n9wxu authored Aug 30, 2022
1 parent dc8f8be commit d91cd6f
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Showing 3 changed files with 50 additions and 24 deletions.
43 changes: 25 additions & 18 deletions portable/GCC/RISC-V/portASM.S
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Original file line number Diff line number Diff line change
Expand Up @@ -98,35 +98,35 @@ definitions. */
/*-----------------------------------------------------------*/

.macro portUPDATE_MTIMER_COMPARE_REGISTER
load_x t0, pullMachineTimerCompareRegister /* Load address of compare register into t0. */
load_x t1, pullNextTime /* Load the address of ullNextTime into t1. */
load_x a0, pullMachineTimerCompareRegister /* Load address of compare register into a0. */
load_x a1, pullNextTime /* Load the address of ullNextTime into a1. */

#if( __riscv_xlen == 32 )

/* Update the 64-bit mtimer compare match value in two 32-bit writes. */
li t4, -1
lw t2, 0(t1) /* Load the low word of ullNextTime into t2. */
lw t3, 4(t1) /* Load the high word of ullNextTime into t3. */
sw t4, 0(t0) /* Low word no smaller than old value to start with - will be overwritten below. */
sw t3, 4(t0) /* Store high word of ullNextTime into compare register. No smaller than new value. */
sw t2, 0(t0) /* Store low word of ullNextTime into compare register. */
li a4, -1
lw a2, 0(a1) /* Load the low word of ullNextTime into a2. */
lw a3, 4(a1) /* Load the high word of ullNextTime into a3. */
sw a4, 0(a0) /* Low word no smaller than old value to start with - will be overwritten below. */
sw a3, 4(a0) /* Store high word of ullNextTime into compare register. No smaller than new value. */
sw a2, 0(a0) /* Store low word of ullNextTime into compare register. */
lw t0, uxTimerIncrementsForOneTick /* Load the value of ullTimerIncrementForOneTick into t0 (could this be optimized by storing in an array next to pullNextTime?). */
add t4, t0, t2 /* Add the low word of ullNextTime to the timer increments for one tick (assumes timer increment for one tick fits in 32-bits). */
sltu t5, t4, t2 /* See if the sum of low words overflowed (what about the zero case?). */
add t6, t3, t5 /* Add overflow to high word of ullNextTime. */
sw t4, 0(t1) /* Store new low word of ullNextTime. */
sw t6, 4(t1) /* Store new high word of ullNextTime. */
add a4, t0, a2 /* Add the low word of ullNextTime to the timer increments for one tick (assumes timer increment for one tick fits in 32-bits). */
sltu t1, a4, a2 /* See if the sum of low words overflowed (what about the zero case?). */
add t2, a3, t1 /* Add overflow to high word of ullNextTime. */
sw a4, 0(a1) /* Store new low word of ullNextTime. */
sw t2, 4(a1) /* Store new high word of ullNextTime. */

#endif /* __riscv_xlen == 32 */

#if( __riscv_xlen == 64 )

/* Update the 64-bit mtimer compare match value. */
ld t2, 0(t1) /* Load ullNextTime into t2. */
sd t2, 0(t0) /* Store ullNextTime into compare register. */
ld t2, 0(a1) /* Load ullNextTime into t2. */
sd t2, 0(a0) /* Store ullNextTime into compare register. */
ld t0, uxTimerIncrementsForOneTick /* Load the value of ullTimerIncrementForOneTick into t0 (could this be optimized by storing in an array next to pullNextTime?). */
add t4, t0, t2 /* Add ullNextTime to the timer increments for one tick. */
sd t4, 0(t1) /* Store ullNextTime. */
sd t4, 0(a1) /* Store ullNextTime. */

#endif /* __riscv_xlen == 64 */
.endm
Expand Down Expand Up @@ -206,7 +206,12 @@ pxPortInitialiseStack:
store_x t0, 0(a0) /* mstatus onto the stack. */
addi a0, a0, -portWORD_SIZE /* Space for critical nesting count. */
store_x x0, 0(a0) /* Critical nesting count starts at 0 for every task. */

#ifdef __riscv_32e
addi a0, a0, -(6 * portWORD_SIZE) /* Space for registers x11-x15. */
#else
addi a0, a0, -(22 * portWORD_SIZE) /* Space for registers x11-x31. */
#endif
store_x a2, 0(a0) /* Task parameters (pvParameters parameter) goes into register X10/a0 on the stack. */
addi a0, a0, -(6 * portWORD_SIZE) /* Space for registers x5-x9. */
load_x t0, xTaskReturnAddress
Expand Down Expand Up @@ -241,6 +246,7 @@ xPortStartFirstTask:
load_x x13, 10 * portWORD_SIZE( sp ) /* a3 */
load_x x14, 11 * portWORD_SIZE( sp ) /* a4 */
load_x x15, 12 * portWORD_SIZE( sp ) /* a5 */
#ifndef __riscv_32e
load_x x16, 13 * portWORD_SIZE( sp ) /* a6 */
load_x x17, 14 * portWORD_SIZE( sp ) /* a7 */
load_x x18, 15 * portWORD_SIZE( sp ) /* s2 */
Expand All @@ -257,12 +263,13 @@ xPortStartFirstTask:
load_x x29, 26 * portWORD_SIZE( sp ) /* t4 */
load_x x30, 27 * portWORD_SIZE( sp ) /* t5 */
load_x x31, 28 * portWORD_SIZE( sp ) /* t6 */
#endif

load_x x5, 29 * portWORD_SIZE( sp ) /* Obtain xCriticalNesting value for this task from task's stack. */
load_x x5, portCRITICAL_NESTING_OFFSET * portWORD_SIZE( sp ) /* Obtain xCriticalNesting value for this task from task's stack. */
load_x x6, pxCriticalNesting /* Load the address of xCriticalNesting into x6. */
store_x x5, 0( x6 ) /* Restore the critical nesting value for this task. */

load_x x5, 30 * portWORD_SIZE( sp ) /* Initial mstatus into x5 (t0). */
load_x x5, portMSTATUS_OFFSET * portWORD_SIZE( sp ) /* Initial mstatus into x5 (t0). */
addi x5, x5, 0x08 /* Set MIE bit so the first task starts with interrupts enabled - required as returns with ret not eret. */
csrrw x0, mstatus, x5 /* Interrupts enabled from here! */

Expand Down
25 changes: 20 additions & 5 deletions portable/GCC/RISC-V/portContext.h
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Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,16 @@
* portasmRESTORE_ADDITIONAL_REGISTERS macros - which can be defined in a chip
* specific version of freertos_risc_v_chip_specific_extensions.h. See the
* notes at the top of portASM.S file. */
#define portCONTEXT_SIZE ( 31 * portWORD_SIZE )
#ifdef __riscv_32e
#define portCONTEXT_SIZE ( 15 * portWORD_SIZE )
#define portCRITICAL_NESTING_OFFSET 13
#define portMSTATUS_OFFSET 14
#else
#define portCONTEXT_SIZE ( 31 * portWORD_SIZE )
#define portCRITICAL_NESTING_OFFSET 29
#define portMSTATUS_OFFSET 30
#endif

/*-----------------------------------------------------------*/

.extern pxCurrentTCB
Expand All @@ -71,6 +80,7 @@
store_x x13, 10 * portWORD_SIZE( sp )
store_x x14, 11 * portWORD_SIZE( sp )
store_x x15, 12 * portWORD_SIZE( sp )
#ifndef __riscv_32e
store_x x16, 13 * portWORD_SIZE( sp )
store_x x17, 14 * portWORD_SIZE( sp )
store_x x18, 15 * portWORD_SIZE( sp )
Expand All @@ -87,12 +97,15 @@
store_x x29, 26 * portWORD_SIZE( sp )
store_x x30, 27 * portWORD_SIZE( sp )
store_x x31, 28 * portWORD_SIZE( sp )
#endif

load_x t0, xCriticalNesting /* Load the value of xCriticalNesting into t0. */
store_x t0, 29 * portWORD_SIZE( sp ) /* Store the critical nesting value to the stack. */
store_x t0, portCRITICAL_NESTING_OFFSET * portWORD_SIZE( sp ) /* Store the critical nesting value to the stack. */


csrr t0, mstatus /* Required for MPIE bit. */
store_x t0, 30 * portWORD_SIZE( sp )
store_x t0, portMSTATUS_OFFSET * portWORD_SIZE( sp )


portasmSAVE_ADDITIONAL_REGISTERS /* Defined in freertos_risc_v_chip_specific_extensions.h to save any registers unique to the RISC-V implementation. */

Expand Down Expand Up @@ -133,10 +146,10 @@
portasmRESTORE_ADDITIONAL_REGISTERS

/* Load mstatus with the interrupt enable bits used by the task. */
load_x t0, 30 * portWORD_SIZE( sp )
load_x t0, portMSTATUS_OFFSET * portWORD_SIZE( sp )
csrw mstatus, t0 /* Required for MPIE bit. */

load_x t0, 29 * portWORD_SIZE( sp ) /* Obtain xCriticalNesting value for this task from task's stack. */
load_x t0, portCRITICAL_NESTING_OFFSET * portWORD_SIZE( sp ) /* Obtain xCriticalNesting value for this task from task's stack. */
load_x t1, pxCriticalNesting /* Load the address of xCriticalNesting into t1. */
store_x t0, 0( t1 ) /* Restore the critical nesting value for this task. */

Expand All @@ -152,6 +165,7 @@
load_x x13, 10 * portWORD_SIZE( sp )
load_x x14, 11 * portWORD_SIZE( sp )
load_x x15, 12 * portWORD_SIZE( sp )
#ifndef __riscv_32e
load_x x16, 13 * portWORD_SIZE( sp )
load_x x17, 14 * portWORD_SIZE( sp )
load_x x18, 15 * portWORD_SIZE( sp )
Expand All @@ -168,6 +182,7 @@
load_x x29, 26 * portWORD_SIZE( sp )
load_x x30, 27 * portWORD_SIZE( sp )
load_x x31, 28 * portWORD_SIZE( sp )
#endif
addi sp, sp, portCONTEXT_SIZE

mret
Expand Down
6 changes: 5 additions & 1 deletion portable/GCC/RISC-V/portmacro.h
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Original file line number Diff line number Diff line change
Expand Up @@ -80,7 +80,11 @@ typedef portUBASE_TYPE TickType_t;
/* Architecture specifics. */
#define portSTACK_GROWTH ( -1 )
#define portTICK_PERIOD_MS ( ( TickType_t ) 1000 / configTICK_RATE_HZ )
#define portBYTE_ALIGNMENT 16
#ifdef __riscv_32e
#define portBYTE_ALIGNMENT 8 /* RV32E uses RISC-V EABI with reduced stack alignment requirements */
#else
#define portBYTE_ALIGNMENT 16
#endif
/*-----------------------------------------------------------*/

/* Scheduler utilities. */
Expand Down

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