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fe310: increase CPU frequency from 16MHz to 320MHz

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This chip can run so much faster! Let's update the default frequency.

Also, change the UART implementation to be more fexible regarding the
clock frequency.
This commit is contained in:
Ayke van Laethem
2021-10-20 02:14:49 +02:00
committed by Ron Evans
parent a5d905f19b
commit 3f89fa0bee
2 changed files with 18 additions and 10 deletions
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src/machine/machine_fe310.go
+12 -4
View File
@@ -9,7 +9,7 @@ import (
)
func CPUFrequency() uint32 {
return 16000000
return 320000000 // 320MHz
}
const (
@@ -61,9 +61,17 @@ var (
)
func (uart *UART) Configure(config UARTConfig) {
// Assuming a 16Mhz Crystal (which is Y1 on the HiFive1), the divisor for a
// 115200 baud rate is 138.
sifive.UART0.DIV.Set(138)
if config.BaudRate == 0 {
config.BaudRate = 115200
}
// The divisor is:
// fbaud = fin / (div + 1)
// Restating to get the divisor:
// div = fin / fbaud - 1
// But we're using integers, so we should take care of rounding:
// div = (fin + fbaud/2) / fbaud - 1
divisor := (CPUFrequency()+config.BaudRate/2)/config.BaudRate - 1
sifive.UART0.DIV.Set(divisor)
sifive.UART0.TXCTRL.Set(sifive.UART_TXCTRL_ENABLE)
sifive.UART0.RXCTRL.Set(sifive.UART_RXCTRL_ENABLE)
sifive.UART0.IE.Set(sifive.UART_IE_RXWM) // enable the receive interrupt (only)
src/runtime/runtime_fe310.go
+6 -6
View File
@@ -79,12 +79,12 @@ func handleInterrupt() {
// initPeripherals configures periperhals the way the runtime expects them.
func initPeripherals() {
// Make sure the HFROSC is on
sifive.PRCI.HFROSCCFG.SetBits(sifive.PRCI_HFROSCCFG_ENABLE)
// Run off 16 MHz Crystal for accuracy.
sifive.PRCI.PLLCFG.SetBits(sifive.PRCI_PLLCFG_REFSEL | sifive.PRCI_PLLCFG_BYPASS)
sifive.PRCI.PLLCFG.SetBits(sifive.PRCI_PLLCFG_SEL)
// Configure PLL to output 320MHz.
// R=2: divide 16MHz to 8MHz
// F=80: multiply 8MHz by 80 to get 640MHz (80/2-1=39)
// Q=2: divide 640MHz by 2 to get 320MHz
// This makes the main CPU run at 320MHz.
sifive.PRCI.PLLCFG.Set(sifive.PRCI_PLLCFG_PLLR_R2<<sifive.PRCI_PLLCFG_PLLR_Pos | 39<<sifive.PRCI_PLLCFG_PLLF_Pos | sifive.PRCI_PLLCFG_PLLQ_Q2<<sifive.PRCI_PLLCFG_PLLQ_Pos | sifive.PRCI_PLLCFG_SEL | sifive.PRCI_PLLCFG_REFSEL)
// Turn off HFROSC to save power
sifive.PRCI.HFROSCCFG.ClearBits(sifive.PRCI_HFROSCCFG_ENABLE)